ew installation
or new batteries. Size and the capacity of the battery bank is irrelevant.

Turn off the b</span><span class="Normal--Char" style=" font-size: 11pt;
">reaker (or remove the fuse) supplying DC power to the system.
Unplug one of
the thermostat leads at the controller.
Using a multi-meter,
read the DC voltage at the battery terminal(s).
Connect the multi-meter
reading DC voltage to the power terminals (+ an</span><span class="Normal--Char" style=" font-size: 11pt;
">d -) on the controller so that it can be left connected and monitored.
Turn on the breaker
(or install the fuse) to the system.
Check that the
voltage is the same as the voltage seen at the battery terminals.
Whilst watching
the multi-meter, reconnect the thermostat lead and monitor the voltage continuously before, during,
and after the compressor starts or attempts to start.

Interpreting results

If the
power supply is free of loose, bad, and/or high resistance connections,
the voltage reading at 5 abo</span><span class="Body-0020Text--Char" style=" font-size: 11pt;
">ve will stay very stable and only drop slightly when the compressor
starts. As a general rule, on a 12v system the reading should not drop
below 12v.
If, when
the compressor attempts to start, the voltage reading drops significantly,
a bad electrical conne</span><span class="Body-0020Text--Char" style=" font-size: 11pt;
">ction should be suspected. If the voltage drop is sufficient to fall
below the 10.5v (23v) cut-off built in to the controller, the compressor
will stop. (At this point the voltage may return to it</span><span class="Body-0020Text--Char" style=" font-size: 11pt;
"></span><span class="Body-0020Text--Char" style=" font-size: 11pt;
">s original reading.) The fan or pump will continue to run f</span><span
class="Body-0020Text--Char" style=" font-size: 11pt;">or approx. 45
seconds and then the compressor will attempt a re-start. If the voltage
is then above 11.5v (23.5v) the compressor will start or attempt to
re-start again. WARNING  If the
multi-meter being used is a digital model that is slow to react, the
v</span><span class="Body-0020Text--Char" style=" font-size: 11pt;">oltage
may drop below 10.5v (23v) and then recover too quickly to register
on the meter. This can lead to the situation where the compressor starts
then stops from low voltage, the voltage returns to it</span><span class="Body-0020Text--Char" style=" font-size: 11pt;
"></span><span class="Body-0020Text--Char" style=" font-size: 11pt;
">s original value, and there being no significant drop on the meter.
If the
compressor starts and runs OK but stops after a short while, the voltage
may be gradually dropping towards and below the 10.5v (23v) cut-off
point. This should be easily identified on the meter.
If the
nature of the fault is such that the voltage reading at 5 above drops below 10.5v (23v) even before the compressor attempts
to start, a very bad electrical connection must be suspected. This is
because even the small load of the fan or pump relay, both less that
0.5 amp (0.25 amp), is seemingly sufficient to reduce the voltage considerably.  

What to look for

   A loose and/or
high-resistance connection can be anywhere in the supply between the
batteries and the controller. i.e. a bad breaker or fuse, a loose or
corroded screw connection, a poorly made or corroded crimp connection,
a damaged section of wire, etc. HINT A good
place to look first is the negative (ground) connection, especially
on a European-built boat. These tend to be multiple, common connections
that are added to over time.

A note on controllers

Older (pre-1995ish) four-pin controllers
for BD2.0, 2.5, and 3.0. The Danfoss version of these controllers had no voltage alarm. The
Frigoboat version has an LED that flashes when the voltage reaches 11.5v
(23.5v) and then gl</span><span class="Body-0020Text--Char" style=" font-size: 11pt;
">ows steadily and stops the compressor when the voltage reaches 10.5v
(23v). The compressor will attempt to start again when the voltage rises
above 11.5v (23v).
Current three-pin controllers for BD35 and BD50. These controllers have provision for a 12v dia</span><span class="Body-0020Text--Char" style=" font-size: 11pt;
">gnostic LED to be connected, and this is a standard feature on the
Frigoboat Smart Speed Control (SSC). This will flash a fault code in
the event of low voltage, high fan/pump-relay current draw, low compressor
RPM, compressor non-start, or electronics ove</span><span class="Body-0020Text--Char" style=" font-size: 11pt;
">rheat.