Dometic tundra Technical Manual page 12

Figure 3.0 - Thermostat Circuit
C. Checking the Thermostat Circuit
1. Remove brown & blue wires from terminal "C" and from
resistor connected to terminal "T". Connect meter leads
to these wires as shown in Figure 3.0 - no polarity is
needed.
2. If the thermostat is working correctly and calling for cool
then the ohmmeter should read zero (0) ohms (the
thermostat must not be in the "OFF" position). If there is
a reading other than zero then do the following:
a. Rotate the thermostat to the coldest setting and see
if that corrects the problem.
b. If there is still no continuity at the wires then un-
screw and remove the thermostat control inside the
unit. Check that wires are not loose and check for
continuity on the thermostat itself (Figure 4.0). If
there is continuity at the thermostat, then there is a
problem with the wires leading back to the module. If
there is no continuity at the thermostat then it should
be replaced.
3. If there appears to be no problem above then check
the resistor that is connected to terminal "T". This
resistor is used to set the compressor motor speed.
Figure 4.0 - Thermostat Inside
Trouble-Shooting
Figure 5.0 -Thermostat Resistor
Connect ohmmeter to either end of resistor assembly
(Figure 5.0). This is a 277-ohm resistor, verify that it is
operating properly to spec (with the 277-ohm resistor,
the control circuit current should be 4mA).
D. Checking the Compressor for Problems
1. Remove all wires from compressor module (make note
where they are connected, see wiring diagram).
2. Unscrew the one mounting screw from the module and
twist module to the rear to disconnect it from compressor.
3. The compressor windings can be checked for defects
by measuring the resistances on the current lead-in
pins (Figure 6.0). If the measured values between all
pins are approximately the same, the compressor motor
is OK.
4. Also check each pin (motor winding) for continuity to
ground. If there is any continuity to ground then the
compressor is internally shorted and will need to be
replaced. This is not a field operation.
5. If a problem is not found in the compressor then the
module will need to be replaced.
Figure 6.0 - Compressor Pins
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