G24M
Service Literature
Corp. 9723-L12 Revised 07-2001 G24M SERIES UNITS
G24M series units are mid-efficiency gas furnaces manufactured with tubular steel heat exchangers formed of aluminized steel. G24M units are available in heating capacities of 45,000 to 140,000 Btuh and cooling applications up to 5 tons. Refer to Engineering Handbook for proper sizing. Units are factory equipped for use with natural gas. A kit is available for conversion to LPG operation. Early model G24M units use electronic (direct spark) ignition. Late model G24M model units feature the Lennox SureLightT silicon-nitride ignition system. The G24MX unit meets the California Nitrogen Oxides (NOx) Standards and California Seasonal Efficiency requirements. All units use a redundant gas valve to assure safety shut-off as required by A.G.A. or C.G.A. Units may be installed in upflow, downflow or horizontal position. The heat exchanger is designed for upright or horizontal use only. When the unit is installed in the downflow position, the heat exchanger is field removed and reinstalled so it is upright when the cabinet is inverted. No field conversion is required when the unit is installed in the horizontal position. The heat exchanger, burners and manifold assembly can easily be removed for inspection and service by simply disconnecting gas, unplugging wiring harness and spark wires and removing four screws holding the heat exchanger in place. Then the heat exchanger slides out of the cabinet.
Model No. G24M2(X)-45 45,000 (13.2) 36,900 (10.8) 80.1% 75.4% All specifications in this manual are subject to change. Procedures outlined in this manual are presented as a recommendation only and do not supersede or replace local or state codes. In the absence of local or state codes, the guidelines and procedures outlined in this manual (except where noted) are recommended only and do not constitute code. SPECIFICATIONS
G24M2-60 G24M3(X)-60 G24M2-75 G24M3(X)-75 Input Btuh (kW) 60,000 (17.6) 75,000 (22.0) Output Btuh (kW) 49,200 (14.4) 61,700 (18.1) lA.F.U.E. 80.5% 80.5% 80.1% 80.0% California Seasonal Efficiency 76.4% 75.9% 76.8% 76.8% Flue size connection diameter -- in. (mm) round 3 (76) 4 (102) Temperature rise range -- _F (_C) 30 - 60 (17 - 33) 45 - 75 (25 - 42) High static certified by A.G.A./C.G.A. -- in wg. (Pa) .50 (125) Gas Piping Size I.P.S. Natural or LPG/propane 1/2 (13) in. 9x7 10 x 7 9x7 10 x 7 Blower wheel nominal mm 229 x 178 254 x 178 229 x 178 254 x 178 diameter x width Blower motor output -- hp (W) 1/4 (187) 1/3 (224) 1/4 (187) 1/3 (224) Tons 1, 1-1/2 or 2 2, 2-1/2 or 3 1, 1-1/2 or 2 2, 2-1/2 or 3 Nominal cooling kW 3.5, 5.3 or 7.0 7.0, 8.8 or 10.6 3.5, 5.3 or7.0 7.0, 8.8 or 10.6 that can be added Shipping weight -- lbs. (kg) 1 package 130 (59) 135 (61) Electrical characteristics 120 volts -- 60 hertz -- 1 phase (less than 12 amps) All models b Optional Accessories (Must Be Ordered Extra) b LPG/propane kit LB-69845L (38K84) Twinning Kit 96J69 -- 5 lbs. (2 kg) Up-Flow/Horizontal Filter and Filter Rack Kits Single (32J02) Ten Pack (66K64) }No. & size of filters - in. (mm) (1) 16 x 20 x 1 (406 x 508 x 25) Catalog No. LB-69843A (32J01) -- 3 lbs. (1 kg) ¡Down-flow No. & Size of Filters -- in. (mm) Filter Kit (2) 16 x 20 x 1 (406 x 508 x 25) Down-flow Combustible Floor Base Sidewall Power Venting Kit Hanging Bracket Kit LB-79239A (67J91) -- 10 lbs. (4 kg) 79J15 -- 25 lbs. (11 kg) LB-69957 (46J66) -- 15 lbs. (8 kg) lAnnual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating for non-weatherized furnaces. }Polyurethane frame type filter is furnished with kit. ¡Filters are not furnished with kit and must be ordered extra. Page 1 ã 1998 Lennox Industries Inc. Litho U.S.A. SPECIFICATIONS
Model No. G24M4(X)-75 G24M3/4(X)-100 G24M4/5(X)-100 Input Btuh (kW) Output Btuh (kW) RA.F.U.E. California Seasonal Efficiency Flue size connection diameter in. (mm) round Temperature rise range EF (EC) High static certified by A.G.A./C.G.A. in wg. (Pa) Gas Piping Size I.P.S. Natural or LPG/propane in. Blower wheel nominal diameter x width mm Blower motor output hp (W) Tons kW Shipping weight lbs. (kg) 1 package Electrical characteristics Nominal cooling that can be added
H 75,000 (22.0) 61,700 (18.1) 80.0% 76.3% 45 - 75 (25 - 42) 100,000 (29.3) 82,000 (24.0) 80.1% 76.5% 4 (102) .50 (125) 1/2 (13) 12 x 8 305 x 203 1/2 (373) 12 x 9 305 x 229 3/4 (560) 80.0% 77.0% 35 - 65 (19 - 36) 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6 7.0, 8.8, 10.6, 12.3 or 14.1 12.3, 14.1, 17.6 or 21.1 140 (64) 175 (79) 175 (79) 120 volts 60 hertz 1 phase (less than 12 amps) All models
Optional Accessories (Must Be Ordered Extra) H
(81J14) LPG/propane kit Twinning Kit Up--Flow/Horizontal Filter and Filter Rack Kits cNo. & size of filters - in. (mm)
o LB-69845L
32J02 (38K84) 96J69 Single ( ) Ten Pack ( ) (1) 16 x 20 x 1 (406 x 508 x 25)
66K64 LB-69845K 5 lbs. (2 kg) Single Ten Pack (1) 20 x 20 x 1 (508 x 508 x 25)
(46J14) (66K65) Down-flow Filter Kit Catalog No. No. & Size of Filters in. (mm) LB-79239A
(67J91) LB-69843A 10 lbs. (4 kg) (32J01) 3 lbs. (1 kg) (2) 16 x 20 x 1 (406 x 508 x 25) LB-79239B 10 lbs. (4 kg) 25 lbs. (11 kg) LB-69957 15 lbs. (8 kg)
(67J92) 79J15 (46J66) Down-flow Combustible floor Base Sidewall Power Venting Kit Hanging Bracket Kit
R c o
furnaces. Filters are not furnished with kit and must be ordered extra. Polyurethane frame type filter is furnished with kit. Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating f or non-weatherized 3DJH SPECIFICATIONS
Input Btuh (kW) 140,000 (41.0) 120,000 (35.2) Output Btuh (kW) 114,800 (33.6) 98,400 (28.8) RA.F.U.E. 80.0% 80.0% 80.1% California Seasonal Efficiency Not Available Not Available 75.5% oFlue size connection diameter in. (mm) round 4 (102) 5 (127) Temperature rise range EF (EC) 45 - 75 (25 - 42) High static certified by A.G.A./C.G.A. in wg. (Pa) .50 (125) .65 (162) Gas Piping Size I.P.S. Natural or LPG/propane - in (mm) 1/2 (13) in. 12 x 8 12 x 9 Blower wheel nominal mm diameter x width 305 x 203 305 x 229 Blower motor output hp (W) 1/2 (373) 3/4 (560) Tons 2, 2-1/2, 3, 3-1/2 or 4 3-1/2, 4, 5 or 6 Nominal cooling kW 7.0, 8.8, 10.6, 12.3 or 14.1 that can be added 12.3, 14.1, 17.6 or 21.1 Shipping weight lbs. (kg) 1 package 190 (86) 175 (79) Electrical characteristics 120 volts 60 hertz 1 phase (less than 12 amps) All models LPG/propane kit Twinning Kit Up--Flow/Horizontal Filter and Filter Rack Kits cNo. and size of filters - in. (mm) Catalog No. wDown-flow No. & Size in. Filter Rack mm of Filters Down-flow Combustible Floor Base Sidewall Power Venting Kit Hanging Bracket Kit
H
Optional Accessories (Must Be Ordered Extra) Model No. G24M3/4-120 G24M4/5(X)-120 G24M4/5-140 R c o w LB-69845K 5 lbs. (2 kg) Single Ten Pack Single Ten Pack (1) 20 x 20 x 1 (508 x 508 x 25) LB-69843A 3 lbs. (1)kg) x 20 x 1 (508 x 508 x 25) (1 20 (2) 16 x 20 x 1 (2) 406 x 508 x 25 LB-79239C LB-79239B 10 lbs. (4 kg) 12 lbs. (5 kg) 25 lbs. (11 kg) LB-69957 15 lbs. (8 kg)
(81J14) 96J69 (46J14) (66K65) (58J93) (66K66) (32J01) (67J92) (67J93) 79J15 (46J66) H Annual Fuel Utilization Efficiency based on U.S. DOE test procedures and according to FTC labeling regulations. Isolated combustion system rating f or non-weatherized Polyurethane frame type filter is furnished with kit. 2 in. x 5 in. (51 mm x127 mm) flue adaptor furnished with -140 input furnaces for connection to furnace induced draft blower. Filters are not furnished with kit and must be ordered extra. furnaces. BLOWER DATA
G24M2-45, G24M2-60 AND G24M2-75 BLOW ER PERFORMANCE
External Static Pressure in. w.g. 0 .05 .10 .15 .20 .25 .30 .40 .50 .60 .70 Pa 0 12 25 37 50 62 75 100 125 150 175 cfm 1270 1245 1220 1195 1170 1140 1110 1060 990 900 800 High L/s 600 590 575 565 550 540 525 500 465 425 380 Air Volume at Various Blower Speeds Medium-High cfm 980 975 975 965 960 950 940 910 880 810 740 L/s 460 460 460 455 455 450 445 430 415 380 350 Medium-Low cfm 770 770 770 765 760 760 760 750 740 690 630 L/s 365 365 365 360 360 360 360 355 350 325 295 cfm 570 565 565 560 560 555 550 545 540 530 520 Low L/s 270 265 265 265 265 260 260 255 255 250 245 NOTE All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table 3DJH BLOWER DATA
G24M3-60 AND G24M3-75 BLOWER PERFORMANCE Air Volume at Various Blower Speeds High Pa cfm L/s Medium-High cfm L/s Medium-Low cfm L/s cfm Low L/s External Static Pressure in. w.g. 0 .05 .10 .15 .20 .25 .30 .40 .50 .60 .70 0 12 25 37 50 62 75 100 125 150 175 1425 1415 1400 1385 1370 1350 1330 1280 1210 1135 1070 670 670 660 655 645 635 630 605 570 535 505 1240 1230 1220 1200 1180 1160 1140 1095 1040 985 920 585 580 575 565 555 545 540 515 490 465 435 1000 995 990 985 980 970 955 925 900 860 800 470 470 465 465 460 460 450 435 425 405 380 800 800 795 795 790 780 770 750 720 680 630 380 380 375 375 375 370 365 355 340 320 300 NOTE All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table G24M4-75, G24M3/4-100 AND G24M3/4-120 BLOWER PERFORMANCE External Static Pressure in. w.g. 0 .05 .10 .15 .20 .25 .30 .40 .50 .60 .70 Pa 0 12 25 37 50 62 75 100 125 150 175 cfm 1830 1815 1800 1875 1750 1725 1700 1650 1600 1550 1480 High L/s 865 855 850 885 825 815 800 780 755 730 700 Air Volume at Various Blower Speeds Medium-High cfm 1600 1585 1570 1550 1530 1515 1500 1460 1420 1380 1330 L/s 755 750 740 730 720 715 710 690 670 650 630 Medium cfm 1325 1320 1315 1310 1300 1290 1275 1245 1210 1170 1130 L/s 625 625 620 620 615 610 600 590 570 550 535 Medium-Low cfm 1070 1070 1070 1065 1060 1050 1040 1020 1000 980 960 L/s 505 505 505 505 500 495 490 480 470 460 455 cfm 880 880 880 875 875 870 870 860 840 820 790 Low L/s 415 415 415 415 415 410 410 405 395 385 375 NOTE All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table 3DJH BLOWER DATA
G24M4/5-100, G24M4/5-120 AND G24M4/5-140 BLOWER PERFORMANCE External Static Pressure in. w.g. 0 .05 .10 .15 .20 .25 .30 .40 .50 .60 .70 Pa 0 12 25 37 50 62 75 100 125 150 175 cfm 2450 2440 2430 2415 2400 2380 2360 2310 2260 2180 2100 High L/s 1155 1150 1145 1140 1135 1125 1115 1090 1065 1030 990 Air Volume at Various Blower Speeds Medium-High cfm 2160 2155 2150 2135 2120 2105 2090 2050 2000 1950 1890 L/s 1020 1015 1015 1010 1000 995 985 965 945 920 890 Medium cfm 1970 1965 1960 1950 1940 1930 1915 1870 1810 1750 1700 L/s 930 925 925 920 915 910 905 880 855 825 800 Medium-Low cfm 1700 1695 1690 1685 1680 1675 1670 1650 1610 1560 1520 L/s 800 800 800 795 795 790 790 780 760 735 715 cfm 1500 1500 1495 1495 1490 1480 1470 1440 1410 1370 1330 Low L/s 710 710 705 705 705 700 695 680 665 645 630 NOTE All air data is measured external to unit with 1 in. (25 mm) cleanable filter (not furnished) in place. Also see Filter Air Resistance table FILTER AIR RESISTANCE
cfm (L/s) 0 (0) in. w.g. (Pa) 0.00 (0) 200 (95) 0.01 (2) 400 (185) 0.03 (7) 600 (280) 0.04 (10) 800 (375) 0.06 (15) 1000 (470) 0.09 (22) 1200 (560) 0.12 (30) 1400 (655) 0.15 (37) 1600 (750) 0.19 (47) 1800 (845) 0.23 (57) 2000 (935) 0.27 (67) 2200 (1030) 0.33 (82) 2400 (1125) 0.38 (95) 2600 (1220) 0.44 (110) 3DJH G24M PARTS IDENTIFICATION
FLUE BOX VENT ADAPTER CABINET TOP HEAT EXCHANGER ASSEMBLY COMBUSTION AIR BLOWER PRESSURE SWITCH PRIMARY LIMIT FRONT LOUVERED PANEL LOW PRESSURE SWITCH (Propane Only) BURNER ASSEMBLY TRANSFORMER NOx TURBULATOR G24M CABINET SECONDARY LIMITS CABINET BOTTOM CONTROL BOARD DOOR INTERLOCK SWITCH BLOWER ASSEMBLY FIGURE 1 HEATING COMPONENTS (shown in horizontal position) PRIMARY LIMIT ROLLOUT SWITCH (2) COMBUSTION AIR PROVE SWITCH ORIFICES MANIFOLD BURNERS Left Bottom Back Front Top Right GAS VALVE HEAT EXCHANGER COLLECTOR COMBUSTION AIR BLOWER FIGURE 2 2=CA $ G24M BURNER ASSEMBLY (shown in upflow position with SureLight ignition system)
SURELIGHT IGNITOR ROLLOUT SWITCHES BURNER BOX TOP VEST PANEL UPPER BURNER MOUNTING RAIL LOWER BURNER MOUNTING RAIL FLAME SENSOR BURNER HEAT EXCHANGER PRIMARY LIMIT Top ORIFICE GAS VALVE Back Left Right BURNER BOX MANIFOLD Front Bottom FIGURE 3 G24M BLOWER DOOR COMPONENTS - BLOWER ACCESS - To Access Blower: 4
J135/ P135 1- Turn off power to unit and disconnect L1 and L2 line voltage power. 2- Disconnect thermostat wiring connections from furnace control board. 3- Remove screws (2) from blower panel. 4- Disconnect J135 from P135 from limit control. 5- Disconnect J43 from blower motor. 6- Remove blower panel and lift from unit. - J1/P1 5
Top Right Back 6 2 3
FIGURE 4
Left Front 1 Bottom Page 7 I-UNIT COMPONENTS (Figures 1, 2, 3)
G24M unit components are shown in figure 1. The blower controls, gas valve and burners can be accessed by re moving the front access panel. A separate blower access door is located behind the front access panel. Electrical control components are mounted to the blower access door. G24M units are factory equipped with bottom return air panels in place. The panels are designed to be field removed as re quired for bottom air return. Indentations on side of units, show where side return opening should be cut during installa tion. DANGER
Shock hazard. Disconnect power before servicing. Control is not field repairable. If control is inoperable, simply replace entire control. Can cause injury or death. Unsafe operation will result if repair is attempted. 3- SureLight Ignition System (A3) Late Model G24M Units
Late model G24M units are equipped with the Lennox SureLight ignition system. The system consists of ignitor (figure 5) and ignition control board (figure 6 with control terminal designations in table 1). The board and ignitor work in combination to ensure furnace ignition and ignitor durability. The SureLight integrated board controls all major furnace operations. The board also features two LED lights for troubleshooting and two accessory termi nals rated at (4) four amps. See table 2 for troubleshoot ing diagnostic codes. Table 3 and 4 show jack plug termi nal designations. Units equipped with the SureLight board can be used with either electronic or electro-me chanical thermostats without modification. The Sur eLight ignitor is made of durable silicon-nitride. Ignitor longevity is also enhanced by voltage ramping by the control board. The board finds the lowest ignitor tempera ture which will successfully light the burner, thus increas ing the life of the ignitor. a-flame sensor The flame sensor uses flame rectification to sense com bustion. During operation, flame is sensed by current passed through the flame and sensing electrode. Figure 7 shows the gap between tip of the electrode and the burner surface. A-Blower Door Components (Figure 4)
Electrical burner control and blower control components are located on the outside surface of the blower access door. Jackplugs allow the blower door to be easily re moved for blower service. Located on the blower door are the unit transformer (T1), the furnace control (A3) and door interlock switch (S51). Furnace control (A3) combines the function of a burner ignition control and blower control. 1- Control Transformer (T1)
A transformer located on the blower door provides power to the low voltage section of the unit. Transformers on all models are rated 30VA with a 120V primary and a 24V sec ondary. 2-Door Interlock Switch (S51)
A door interlock switch rated 16A at 125VAC is located on the blower access door. The switch is wired in series with line voltage. When the blower door is removed the unit will shut down. SURELIGHT IGNITOR SURELIGHT IGNITOR BURNER ASSEMBLY UPPER BURNER MOUNTING RAIL FLAME RETENTION RING ORIFICE FLAME SENSOR FIGURE 5 Page 8 SURELIGHT CONTROL BOARD LATE MODEL G24M UNITS TABLE 1
SURELIGHT CONTROL TERMINAL DESIGNATIONS ACB COOL Blower - Cooling Speed (Line Volt) ACB HEAT Blower - Heating Speed (Line Volt) PARK Alternate Blower Speeds (Dead) ACB LOW Continuous Low Speed Blower ACC Accessory Terminal (Line Volt) TX 120VAC Hot to Transformer HOT 120VAC Hot Input HTG ACC Heat Only Accessory (Line Volt) NEUTRALS 120VAC Neutrals 24VAC HOT 24VAC Hot from Transformer 24VAC RTN 24VAC Return from Transformer FLAME SENSE Flame Sense Terminal
NORMAL FLAME SIGNAL > 0.7 MICROAMPS LOW FLAME SIGNAL < 0.7 MICROAMPS MINIMUM FLAME SIGNAL < 0.15 MICROAMPS FLAME SENSOR TO BURNER GAP
1/4 in. 7 mm ¦ 1/32 in. 0.79 mm BURNER 11/16 in. 18 mm ¦ 1/32 in. 0.79 mm 3/16 in. 4.7 mm FLAME SIDE VIEWSENSOR END VIEW FIGURE 6 TABLE 2 FIGURE 7 DIAGNOSTIC CODES
MAKE SURE TO ID LED'S CORRECTLY: REFER TO INSTALLATION INSTRUCTIONS FOR CONTROL BOARD LAYOUT. LED #1
SIMULTANEOUS SLOW FLASH SIMULTANEOUS FAST FLASH LED #2
SIMULTANEOUS SLOW FLASH SIMULTANEOUS FAST FLASH DESCRIPTION
Power - Normal operation Also signaled during cooling and continues fan. Normal operation - signaled when heating demand initiated at thermostat. Primary or Secondary limit open. Units with board 63K8901 or 24L85: Limit must close within 5 trials for ignition or board goes into one hour limit Watchguard. Units with board 56L83 or 97L48: Limit must close within 3 minutes or board goes into one hour limit Watchguard. Pressure switch open or has opened 5 times during a single call for heat; OR: Blocked inlet/exhaust vent; OR: Condensate line blocked; OR: Pressure switch closed prior to activation of combustion air blower. Watchguard - burners fail to ignite. Flame sensed without gas valve energized. Rollout switch open. OR: 9 pin connector improperly attached. Circuit board failure or control wired incorrectly. Main power polarity reversed. Switch line and neutral. Low flame signal. Measures below .7 microAmps. Replace flame sense rod. Improper main ground or line voltage below 75 volts; OR: Broken ignitor; OR: Open ignitor circuit. SLOW FLASH ON OFF ALTERNATING SLOW FLASH SLOW FLASH ON ON ON OFF FAST FLASH SLOW FLASH ALTERNATING FAST FLASH SLOW FLASH ALTERNATING SLOW FLASH OFF SLOW FLASH ON OFF ON SLOW FLASH FAST FLASH ALTERNATING FAST FLASH NOTE - Slow flash equals 1 Hz (one flash per second). Fast flash equals 3 Hz (three flashes per second). Drop out flame sense current < 0.15 microAmps Page 9 TABLE 3
SureLight BOARD J156 (J2) TERMINAL DESIGNATIONS PIN # 1 FUNCTION Ignitor Not Used Ignitor Neutral Combustion Air Blower Line Voltage Not Used Combustion Air Blower Neutral not proven within 2-1/2 minutes, the control goes into Watchguard-Pressure Switch mode for a 5-minute re-set period. NOTE - The G24M furnace contains electronic components that are polarity sensitive. Make sure that the furnace is wired correctly and is properly grounded. After the 15-second pre-purge period, the SureLight ignitor warms up for 20 seconds after which the gas valve opens for a 4-second trial for ignition. The ignitor stays energized for the first second of the 4-second trial. G24M units with 63K89, 24L85 or 56L83: the ignitor stays energized the first second of the 4 second trial. G24M units with board 97L48: ignitor stays energized during the 4-second trial until flame is sensed. If ignition is not proved during the 4-second period, the control will try four more times with an inter purge and warm-up time between trials of 35 seconds. After a total of five trials for ignition (including the initial trial), the control goes into Watchguard-Flame Failure mode. After a 60-minute reset period, the control will begin the ignition sequence again. The SureLight control board has an added feature that prolongs the life of the ignitor. After a successful ignition, the SureLight control utilizes less power to energize the ignitor on successive calls for heat. The control continues to ramp down the voltage to the ignitor until it finds the lowest amount of power that will provide a successful ignition. This amount of power is used for 255 cycles. On the 256th call for heat, the control will again ramp down until the lowest power is determined and the cycle begins again. c-Fan Time Control The fan on time of 45 seconds is not adjustable. Fan off time (time that the blower operates after the heat demand has been satisfied) can be adjusted by flipping the dip switches located on the SureLight integrated control. The unit is shipped with a factory fan off setting of 90 seconds. Fan off time will affect comfort and is adjustable to satisfy individual applications. See figure 8. NOTE--If fan "off" time is set too low, residual heat in heat exchanger may cause primary limit S10 to trip resulting in frequent cycling of blower. If this occurs, adjust blower to longer time setting. FAN-OFF TIME ADJUSTMENT
60sec. 90sec. 120sec. 180sec. 2 3 4 5 6 TABLE 4
SureLight BOARD J58 (J1) TERMINAL DESIGNATIONS PIN # 1 FUNCTION Primary Limit In Gas Valve Common Roll Out Switch Out Gas Valve 24V Pressure Switch In Pressure Switch and Primary Limit Out Not Used Roll Out Switch In Ground 2 3 4 5 6 7 8 9 ELECTROSTATIC DISCHARGE (ESD) Precautions and Procedures CAUTION
Electrostatic discharge can affect electronic components. Take precautions during furnace installation and service to protect the furnace's electronic controls. Precautions will help to avoid control exposure to electrostatic discharge by putting the furnace, the control and the technician at the same electrostatic potential. Neutralize electrostatic charge by touching hand and all tools on an unpainted unit surface, such as the gas valve or blower deck, before performing any service procedure. b-Electronic Ignition On a call for heat the SureLight control monitors the combustion air inducer prove switch. The control will not begin the heating cycle if the prove switch is closed (by-passed). Once the prove switch is determined to be open, the combustion air inducer is energized. When the differential in the prove switch is great enough, the prove switch closes and a 15-second pre-purge begins. If the prove switch is To adjust fan-off timing, flip dip switch to desired setting. FIGURE 8 Page 10 4-- Ram Control (A3) Early Model G24M Units
The furnace control combines burner ignition functions with blower control functions. Early model G24M units utilize a furnace control Ignition Control The ignition control is a direct spark ignition control module integral to the furnace control. See figure 9. When there is a call for heat, the control delays ignition until combustion air blower operation has been proved and pre-purge period has elapsed. It then opens the gas valve and generates a spark to ignite the burners. Trial for ignition lasts for 7 seconds. At the same time, the control begins monitoring the flame sensor. If the flame current is too weak (less than 1 microamp) or if the burners do not ignite (within the 7 second ignition trial), the control will shut off the spark ignitor and the combustion air blower and de-energize the gas valve. Flame current should be between 1 and 5 microamps to keep the gas valve open. See figure 21. The control will attempt to ignite the burners up to two more times. Each time the control restarts the ignition sequence, it begins with a 45 second pre-purge. If flame is not sensed after the third trial, the control locks out. Lockout means that the control shuts off the gas valve, spark and combustion air blower for 60 minutes. At the end of 60 minutes the control completely resets and will attempt ignition up to three times. The control can be manually reset before the end of 60 minutes by momentarily turning off power to the unit. manufactured by RAM Electronics Corporation. The RAM board is a printed circuit board which controls the blower, gas valve, combustion air blower and ignition spark. It also monitors the flame, limit and gas valve operation. The control has a non-adjustable, factory preset on fan timing (45 seconds). Fan off timings are adjustable. The board utilizes both 120 and 24VAC. See figure 9. The board is also equipped with a diagnostic LED for use when troubleshooting the unit. When the furnace is idle (blower off and no heating or cooling demand), the diagnostic LED flashes at a slow steady rate. On a call for heat, the diagnostic LED begins flashing at a fast rate and the combustion air blower is energized. The LED flashes different codes to indicate problem conditions. The diagnostic LED lights red (not flashing) to indicate control board failure. Table 7 shows how to interpret the other LED modes. Pre-Purge On a call for heat, the combustion air blower begins operating. If the combustion air prove switch closes, the combustion air blower continues to operate for 45 seconds (pre-purge) before allowing ignition. Prepurge allows the heat exchanger to be cleared of combustion products and to introduce fresh air for combustion. If the combustion air prove switch does not close, the combustion air blower continues to run indefinitely (until the prove switch closes). Post-Purge After a demand, the combustion air blower continues to operate for 5 seconds (post-purge) before stopping. Post-purge allows the heat exchanger to be cleared of combustion products. DANGER
Shock hazard. Spark related components contain high voltage. Disconnect power before servicing. Control is not field repairable. If control is inoperable, simply replace entire control. Can cause injury or death. Unsafe operation will result if repair is attempted. Page 11 EARLY MODEL G24M FURNACE CONTROL (A3)
SPARK OUTPUT 24VAC VOLT TERMINAL CONNECTIONS LINE VOLTAGE TERMINAL CONNECTIONS See Table 6 for Terminal Functions PLUG P20 FAN-OFF TIMING SWITCHES THERMOSTAT CONNECTIONS DIAGNOSTIC LED FIGURE 9 TABLE 5 When flame is sensed, the indoor blower starts after a 45 second delay. Gas valve remains open and blower continues to run until demand stops, flame sensor senses loss of flame, a limit opens or the prove switch opens. If any of these events occur during a thermostat demand, the gas valve closes and the diagnostic
On (Spark On Starts Within 0.8 seconds) On Fast Flash .Krnace Control A3 Limit Response During Operation Response Condition
Loss of Flame Sensed Before End of 45 second Blower On Delay (3 or Fewer Trials for Ignition) Loss of Flame Sensed After 45 second Blower On Delay (3 or Fewer Trials for Ignition) Loss of Flame Sensed (More Than 3 Trials for Ignition) Flame Sensed Without Demand Primary or Secondary Limit Open Rollout Switch Open Combustion Air Prove Switch Open On Off On 3 Flashes On Off On 4 Flashes On Off On 4 Flashes On Off On 5 Flashes Off Off Off 2 Flashes On Off Then On With Spark After PrePurge On Fast Flash Combustion Air Blower Gas Valve Supply Air Blower Diagnostic LED LED registers the error condition (table 5). Blower Control and Timings DANGER
Electrical Shock Hazard. This control contains field adjustable switches and also contains line voltage. Make sure power is disconnected before making any field adjustments or performing any service procedure.
NOTEIf fan off time is set too low, residual heat in heat exchanger may cause primary limit S10 to trip resulting in frequent cycling of blower. If this occurs, adjust blower to longer time setting. Fan ON timing (time that the burners operate before the supply air blower starts) is fixed at 45 seconds and cannot be adjusted. Fan OFF timings (time that the blower operates after a heating or cooling demand has been satisfied) are determined by the arrangement of switches on the furnace control board. See figure 9. To adjust fan off timings, gently reposition the switches to a new timing Page 12 position. Figure 10 shows the various fan off timings and how switches should be positioned. Unit is shipped with a factory fan off setting of 180 seconds. Fan off time will affect comfort and efficiency and is adjustable to satisfy individual applications. The fan off timing is initiated after a heating or cooling demand but not after a blower demand (that is, when indoor thermostat switch is changed from ON to AUTO and heating/cooling demand is not present, the blower stops immediately).
Two Flashes TABLE 7
LED State
Steady On Slow Flash Furnace Control A3 Diagnostic LED Meaning Remedy
Control Failure Normal Operation and No Call For Heat Normal Operation with Call For Heat Replace Control - - - - Fast Flash - - - Failed to Sense or Sustain Flame. Check Gas Valve, FURNACE CONTROL A3 TERMINAL DESIGNATIONS Terminal Type Function
24VAC HOT GND Y G R W C 120VAC HOT 120VAC RTN 120VAC TX CMB CMB RTN ACB HEAT 1/4 Spade 1/4 Spade Screw Strip Screw Strip Screw Strip Screw Strip Screw Strip 1/4 Spade 1/4 Spade 1/4 Spade J20/P20 Pin 1 J20/P20 Pin 2 1/4 Spade 24V AC In From Transformer To Cabinet Ground Cooling Demand Blower Demand 24VAC to Thermostat Heating Demand 24VAC Common Line Voltage In Line Voltage Neutral Line Voltage Out T Transformer o Switched 120VAC to Combustion Air Blower 120VAC Common Combustion Air Blower Switched 120VAC to Blower Heating Tap 120VAC Output to Supply Air Blower for Continuous Operation During No Demand Switched 120VAC to Blower Cooling Tap 24VAC to Gas Valve 24VAC Common From Gas Valve 24VAC In From Pressure Switch Switch Open: Prohibits Ignition Switch Closed: Allows Ignition 24VAC In From Limits Limit Open: Closes Gas Valve Limits Closed: Allows Ignition 24VAC to Limit Train and Pressure Switch 24V AC Out T Rollout Switches o 24VAC In From Rollout Switches High Voltage Out T o Spark Electrode Flame Microamp Sensing
Five Flashes Flame Sensed and Gas Valve Not Energized. Four Flashes Open Limit Three Flashes Pressure Switch Open TABLE 6 Control Lockout Burners, Spark Electrode and Wire, Flame Sensor. Replace Control If All OK. Failed to Prove Combustion Blower Operation or Blocked Vent. Repair or Replace as Necessary. Check Primary Limit, Rollout Switches and Secondary Limits. Find source of Overtemperature. If all OK, Reset or Replace Limits as Necessary. Check Gas Valve. If OK, Check Flame Sensor. B--Blower Motors and Capacitors
All G24M units use direct drive blower motors. All motors used are 120V permanent split capacitor motors to ensure maximum efficiency. See table8 for ratings. ACB LOW 1/4 Spade TABLE 8 G24M BLOWER RATINGS 120V 1PH
BLOWER MOTOR G24MQ2 G24MQ3 G24MQ3/4 G24MQ4 G24MQ4/5 G24MQ5/6 HP 1/4 1/3 1/2 1/2 3/4 3/4 CAP 5MFD 370V 5MFD 370V 7.5MFD 370V 7.5MFD 370V 40MFD 370V 40MFD 370V ACB COOL VLV HOT VLV RTN 1/4 Spade J20/P20 Pin 13 J20/P20 Pin 9 J20/P20 Pin 10 J20/P20 Pin 11 J20/P20 Pin 14 J20/P20 Pin 7 J20/P20 Pin 15 Male Spark Plug Type J20/P20 Pin 12 PSW IN HIL IN SUPPLY AIR BLOWER AND SECONDARY LIMITS
SECONDARY LIMITS (S21) HIL OUT RO OUT RO IN SPARK ELECTRODE FS Top Left Front Bottom Back Right FAN-OFF TIME ADJU LOCATED ON FURNACE CONTROL (A3) STMENT SWITCHES
Fan-Off Timings Switch 1 Off Off On On 2 Off On Off On Timing Seconds 90 120 180 240 BLOWER MOTOR MOTOR CAPACITOR To Remove Blower From Unit: Remove Bolts and Wiring Jackplugs. Then Slide Out Front of Unit. FIGURE 10 Diagnostic LED
The furnace control is equipped with a diagnostic LED used for troubleshooting the unit and the control. LED functions are shown in table 7. FIGURE 11 Page 13 C--Combustion Air Blower (B6)
All G24M units use a combustion air blower to move air through the burners and heat exchanger during heating operation. Some early model G24M units are equipped with a blower that uses a PSC (Permanent Split Capacitor) 120VAC motor. PSC motors use run capacitors. Other early and late model G24M units are equipped with a blower that uses a shaded pole 120V motor. The motor operates during all heating operation and is controlled by furnace control A3. For G24M units equipped with the Ram ignition system, the blower will operate for 45 seconds before burner ignition (pre-purge) and for 5 seconds after the gas valve closes (post-purge). For G24M units equipped with the SureLight ignition system, the blower will operate for 15 seconds before burner ignition (pre purge) and for 5 seconds after the the gas valve closes (post purge). A pressure switch connected to the combustion air blower housing is used to prove combustion air blower operation. The switch monitors air pressure in the blower housing. During normal operation, the pressure in the housing is negative. If pressure becomes less negative (signifying an obstruction) the pressure switch opens. When the pressure switch opens, the furnace control (A3) immediately closes the gas valve to prevent burner operation. E--Primary Limit Control (S10)
LIMIT CONTROL FOR G24M SERIES UNITS
THIS TYPE AUTO-RESET LIMIT IS USED FOR THE PRIMARY LIMIT (S10) AND RIGHT SECONDARY LIMIT (S21) (see FIGURE 11) FIGURE 13 The primary limit (S10) on G24M units is located in the middle of the heating vestibule panel. When excess heat is sensed in the heat exchanger, the limit will open. If the limit is tripped, the furnace control energizes the supply air blower and closes the gas valve. The limit automatically resets when unit temperature returns to normal. The switch is factory set and cannot be adjusted. The switch may have different setpoints for each unit model number. However, the setpoint will be printed on the side of the limit. F--Secondary Limit Controls (S21)
The secondary limit (S21) on G24M units is located in the blower compartment in the back side of the blower housing. When excess heat is sensed in the blower compartment, the limit will open. If the limit is tripped, the furnace control energizes the supply air blower and closes the gas valve. The limit automatically resets when unit temperature returns to normal. The switch is factory set and cannot be adjusted. Two limits are supplied in each furnace and each limit is a different style (figures 13 and 14). The setpoint will be printed on the side of the limit. If stick limit (figure 14) suffers from nuisance trips anf the furnace is in the horizontal position, replace with limit kit no. 50L98. SECONDARY LIMIT CONTROL (S21) FOR G24M SERIES UNITS D--Flame Rollout Switches (S47)
Flame rollout switch is a high temperature limit located on top of the burner box. Each furnace is equipped with two identical switches. One switch is located over the leftmost burner and the other switch is located over the rightmost burner. The limit is a N.C. SPST manual-reset limit connected in series with the ignition control A3. When S47 senses rollout, the ignition control immediately stops ignition and INSULATING COVER closes the gas valve. If unit is running and flame rollout is detected, the gas valve will close and ignition control will be disabled. Rollout can be caused by a blocked flue or lack of combustion air. The switch is factory set and cannot be adjusted. The setpoint will be printed on the side of the limit. The switch can be manually reset. To manually reset a tripped switch, push the reset button located on the control. ROLLOUT SWITCH (S47) THIS TYPE AUTO-RESET LIMIT IS USED FOR THE LEFT SECONDARY LIMIT (S21) (see FIGURE 11) SPADE CONNECTORS LIMIT MANUAL RESET BUTTON
FIGURE 12 G--Spark Electrode and Flame Sensor Early Model G24M Units
Figure 15 shows the arrangement of flame sensor, spark electrode and burners. The ignition control uses direct spark to ignite the rightmost burner and the burners cross-light to the left. The flame sensor uses flame rectification to sense combustion. A flame retention ring in the end of each burner is used to maintain correct flame length and shape and to keep the flame from lifting off the burner head. Figure 16 shows the gap between tip of the electrodes and the burner surface. LIMIT INSULATING COVER (s)
FIGURE 14 Page 14 TYPICAL BURNER/ELECTRODE ORIENTATION view looking at flame end of burners
1/8(+1/64) UPPER BURNER MOUNTING RAIL BURNER MANIFOLD ORIFICE Right Top Left Bottom GROUND SPARK ELECTRODE FLAME RETENTION RING LOWER BURNER MOUNTING RAIL FLAME SENSOR (SOME UNITS MAY HAVE SENSOR LOCATED IN MIDDLE OF BURNER) FIGURE 15
TYPICAL ACCESS TO REGULATOR FOR ADJUSTMENT AND L.P CHANGEOVER .
(Honeywell VR8205 series gas valve shown) SPARK ELECTRODE TO BURNER GAP F
BURNER 1/4 in. 7 mm 1/32 in. 0.79 mm 3/16 in. 4.7 mm 11/16 in. 18 mm 1/32 in. 0.79 mm F 287/(7 35(6685( 7$3 ,1/(7 35(6685( 7$3 SIDE VIEWSENSOR
FIGURE 16 FLAME END VIEW *$6 9$/9( 6+2:1 ,1 2)) 326,7,21
&$3 6&5(: %ODFN 35(6685( 635,1* 7DSHUHG (QG 'RZQ 5HG ,1/(7 35(6685( 7$3 H--Gas Valve
The G24M uses a gas valve manufactured by Honey- 5(*8/$725 $'-867,1* 6&5(: :KLWH well (figure 17) or White Rodgers (figure 18). The valve is internally redundant to assure safety shut-off. If the gas valve must be replaced, the same type valve must be used. 24VAC terminals and gas control knob are located on top of the valve. All terminals on the gas valve are connected to wires from the electronic ignition control. 24V applied to the terminals energizes the valve. Inlet and outlet pressure taps are located on the valve. A regulator adjustment screw is located on the valve. Refer to figure 17 or 18 for location of valve features. An LPG changeover kit is available from Lennox. The kit includes burner orifices and a regulator conversion kit. *$6 ,1/(7 FIGURE 17 WHITE RODGERS
GAS VALVE KNOB SHOWN IN OFF POSITION I--Combustion Air Blower Prove (Pressure) Switch (S64)
G24M series units are equipped with a combustion air prove switch located on the vestibule panel. The switch is connected to the combustion air blower housing by means of a flexible silicone hose. It monitors air pressure in the combustion air blower housing. 36E GAS VALVE REGULATOR COVER SCREW GAS INLET 35(6685( 7$3 35(6685( 7$3 FIGURE 18 Page 15 The switch is a single-pole single-throw pressure switch electrically connected to the furnace control. The purpose of the switch is to prevent burner operation if the combustion air blower is not operating.
PROVE SWITCH
COMBUSTION AIR BLOWER PROVE SWITCH Normally Open Closes on Negative Pressure III--START-UP A--Preliminary and Seasonal Checks
1 - Inspect electrical wiring, both field and factory installed for loose connections. Tighten as required. 2 - Check voltage at disconnect switch. Voltage must be within range listed on the nameplate. If not, consult the power company and have voltage condition corrected before starting unit. B--Heating Start-Up
1 - Set thermostat to OFF position. Close manual knob on gas valve. 2 - Wait 5 minutes. Sensing Tube Attaches to Top Side Of Blower 3 - Open manual knob on gas valve, replace burner access door and turn on unit electrical supply. Back PROVE SWITCH Left Top Right WARNING
Shock and burn hazard. G24M units are equipped with either a direct spark
Front or hot surface ignition system. Do not attempt to light manually. Bottom FIGURE 19 4 - Set fan switch to AUTO or ON and move system selection switch to HEAT. Adjust thermostat to a setting above room temperature. 5 - If unit does not light the first time, the SureLight control will attempt four more ignitions, the Ram control will attempt two more ignitions before locking out. 6 - If lockout occurs, repeat steps 1, 2, 3 and 4. - On start-up, the switch senses that the combustion air blower is operating. It closes a circuit to the furnace control when pressure inside the combustion air blower increases above switch setting (negative) w.c. The pressure sensed by the switch is relative to atmospheric pressure. If the flue becomes obstructed during operation, the switch senses a loss of negative pressure (pressure becomes more equal with atmospheric pressure) and opens the circuit to the furnace control and gas valve. The switch trip pressure is different depending on unit model number. The trip pressure is printed on the side of the limit. The switch is factory set and is not field adjustable. It is a safety shut-down control in the furnace and must not be bypassed for any reason. C--Safety or Emergency Shutdown
Turn off unit power. Close manual and main gas valves. IMPORTANT
In case emergency shutdown is required, turn off the main shut-off valve and disconnect the main power to unit. These controls should be properly labeled by the installer. II--PLACEMENT AND INSTALLATION
Make sure unit is installed in accordance with installation instructions and applicable codes. D--Extended Period Shutdown
Turn off thermostat or set to UNOCCUPIED mode. Close all gas valves (both internal and external to unit) to guarantee no gas leak into combustion chamber. Turn off power to unit. All access panels, covers and vent caps must be in place and secured. Page 16 IV--HEATING SYSTEM SERVICE CHECKS A--A.G.A./C.G.A. Certification
All units are A.G.A. design certified without modifications. Refer to the G24M Operation and Installation Instruction Manual for Information. underfire. High pressure can result in permanent damage to gas valve or overfire. For natural gas units, operating pressure at unit gas connection must be between 5.0 W.C. and 13.0 W.C. For L.P gas units, . operating pressure at unit gas connection must be between 10.0 W.C. and 13.0 W.C. On multiple unit installations, each unit should be checked separately, with and without other units operating. Supply pressure must fall within range listed in previous paragraph. B--Gas Piping
Gas supply piping should not allow more than 0.5W.C. drop in pressure between gas meter and unit. Supply gas pipe must not be smaller than unit gas connection. Compounds used on gas piping threaded joints E--Check Manifold Pressure
After line pressure has been checked and adjusted, check manifold pressure. Move pressure gauge to outlet pressure tap located on unit gas valve (GV1). Checks of manifold pressure are made as verification of proper regulator adjustment. Manifold pressure for the G24M can be measured at any time the gas valve is open and is supplying gas to the unit. Normal manifold pressure for natural gas units is 3.5 in. w.c. For LP/propane gas the correct manifold pressure is 9.5 in. w.c. should be resistant to action of liquefied petroleum gases. C--Testing Gas Piping
When pressure testing gas lines, the gas valve must be disconnected and isolated. Gas valves can be damaged if subjected to more than 0.5psig (14 W.C.). See figure 20. If the pressure is equal to or less than 0.5psig (14W.C.), use the manual shut-off valve before pressure testing to isolate furnace from gas supply.
GAS PIPING TEST PROCEDURE
MANUAL MAIN SHUT-OFF VALVE WILL NOT HOLD TEST PRESSURE IN EXCESS OF 0.5 PSIG (14W.C.) IMPORTANT
For safety, connect a shut-off valve between the manometer and the gas tap to permit shut off of gas pressure to the manometer. TABLE 9 GAS VALVE REGULATION
Unit (Fuel) Natural CAP GAS VALVE L.P . Operating Pressure (outlet) in. W.C. 3.5 +0 -0.3 9.5 + 0.5 The gas valve is factory set and should not require adFIELD PROVIDED LINE PRESSURE TAP justment. All gas valves are factory regulated. See table 9.
Manifold Adjustment Procedure: FIGURE 20 When checking piping connections for gas leaks, use preferred means. Kitchen detergents can cause harmful corrosion on various metals used in gas piping. Use of a specialty Gas Leak Detector is strongly recommended. It is available through Lennox under part number 1 - Connect a test gauge to outlet pressure tap on gas valve. Start unit and allow 5 minutes for unit to reach steady state. 2 - While waiting for the unit to stabilize, notice the flame. Flame should be stable and should not lift from burner. Natural gas should burn blue. L.P gas . should burn mostly blue with some orange streaks. 3 - After allowing unit to stabilize for 5 minutes, record manifold pressure and compare to values given in table 9. NOTE-Shut unit off and remove manometer as soon as an accurate reading has been obtained. Take care to replace pressure tap plug. 31B2001. See Corp. 8411-L10, for further details. Do not use matches, candles, flame or any other source of ignition to check for gas leaks. D--Testing Gas Supply Pressure
When testing supply gas pressure, connect test gauge to inlet pressure tap (field provided). See figure 20. Check gas line pressure with unit firing at maximum rate. Low pressure may result in erratic operation or Page 17 F- Proper Gas Flow TABLE 11
ALTITUDE feet (m) 0 - 4500 (0 - 1372) 4500 - 5500 (1372 - 1676) 5500 - 6500 (1676 - 1981) 6500 - 7500 (1372 - 2286) GAS FUEL Natural Propane/LP Natural Propane/LP Natural Propane/LP Natural Propane/LP MANIFOLD PRESSURE in. W.C. (kPa) 3.5 (0.87) 9.5 (2.36) 3.4 (0.86) 9.2 (2.29) 3.3 (0.82) 8.9 (2.21) 3.2 (0.80) 8.6 (2.14) Furnace should operate at least 5 minutes before check ing gas flow. Determine time in seconds for two revolu tions of gas through the meter. (Two revolutions assures a more accurate time.) Divide by two and compare to time in table 10 below. Adjust manifold pressure on gas valve to match time needed. NOTE- To obtain accurate reading, shut off all other gas appliances connected to meter. TABLE 10 GAS METER CLOCKING CHART Seconds for One Revolution Natural LP G24M Unit 1 cu ft 2 cu ft 1 cu ft 2 cu ft Dial Dial Dial DIAL -45 80 160 200 400 -60 60 120 150 300 -75 48 96 120 240 -100 36 72 90 180 -120 30 60 75 150 -140 26 52 64 128
Natural-1000 btu/cu ft LP-2500 btu/cu ft Unit Model G24M-45 G24M-60 G24M-75 G24M-100 G24M-120 G24M-140 TABLE 12 Pressure Switch Part Number No Change No Change 88J8001 18L2401 18L2401 No Change IMPORTANT
For safety, shut unit off and remove manometer as soon as an accurate reading has been obtained. Take care to replace pressure tap plug. NOTE- To obtain accurate reading, shut off all other gas appliances connected to meter. G-High Altitude Derate NOTE-In Canada, certification for installation at alti tudes over 4500 ft. (1372m) above sea level is the juris diction of the local authorities. H-Flame Signal
A microamp DC meter is needed to check the flame signal on the primary ignition control. Flame (microamp) signal is an electrical current which passes from the furnace control through the sensor elec trode during unit operation. Current passes from the sen sor through the flame to ground to complete a safety cir cuit. To Measure Flame Signal: 1 - Place meter in series between furnace control and sensor wire. Connect the positive (+) lead of meter to the ignition control sensor connection and the nega tive (-) lead of the meter to the sensor wire. See figure 21. 2 - Set thermostat for a heating demand and check flame signal with unit operating. For G24M series with a RAM control, a reading of 1 to 5 microamps DC should occur. The furnace control must see at least 1.0 microamps in order to keep the gas valve energized. G24M units with the SureLight control should read 0.7 microamps or more. G24M-1 through -9 Models This unit does not require gas pressure adjustment, or pressure switch change when operating at elevations of 0 to 7500 ft. (0 to 2248m). Check gas line pressure with unit firing. The minimum pressure as shown on the nameplate for natural and propane gases must be maintained. No ori fice change is required. NOTE-This is the only permissible field derate for this appliance. G24M-10 and -11 Models Table 11 shows manifold pressure settings for installations at different altitudes. Refer to table 12 for pressure switch replacement for models at elevations of 4500 feet (1372m) and greater. Page 18 FLAME SIGNAL TEST
D.C. MICROAMP METER FLAME SENSOR IGNITION CON TROL SENSOR WIRE RAM CONTROL SHOWN SENSE" TERMINAL set for unit operation within the range of AIR TEMP. RISE °F" listed in the unit rating plate. To Measure Temperature Rise: 1 - Place plenum thermometers in the supply and return air plenums. Locate supply air thermometer in the first horizontal run of the plenum where it will not pick up ra diant heat from the heat exchanger. 2 - Set thermostat to highest setting. 3 - After plenum thermometers have reached their high est and steadiest readings, subtract the two readings. The difference should be in the range listed on the unit rating plate. If the temperature is too low, decrease blower speed. If temperature is too high, first check the firing rate. Provided the firing rate is acceptable, in crease blower speed to reduce temperature. To change blower speed taps see the Blower Speed Taps section in this manual. FIGURE 21 Flame signal from the Ram control may rise above 5 micro amps for the first few seconds after ignition then level off within the range. WARNING
Fire and explosion hazard. These instructions MUST be followed exactly. Can cause a fire or explosion resulting in property damage, personal injury or loss of life. C-External Static Pressure
1 - Measure tap locations as shown in figure 22. 2 - Punch a 1/4" diameter hole STATIC PRESSURE TEST in supply and return air ple V-TYPICAL OPERATING CHARACTERISTICS A-Blower Operation and Adjustment
NOTE- The following is a generalized procedure and does not apply to all thermostat controls. 1 - Blower