Service manual

14
2. “The selector switch could be open.” Rotate the
selector switch and check for continuity between the
appropriate terminals.
Terminals Switch Position
L-1-3 Lo Heat
L-1 Lo Fan
L-2 Hi Fan
L-1-4 Lo Cool
L-2-4 Hi Cool
Notice that when we are using an ohm meter, the
power must be turned off. It is also important to
disconnect all wires from a conductor being checked
with an ohm meter to prevent any chance of
feedback.
Problem
2. Inadequate Cooling
The customer says he gets inadequate cooling for a while
after he turns the system on and then it seems to quit cooling
completely. As soon as the housing is removed from the unit
with the system running, we observe that the suction line is
coated with frost.
Question: “Could the system be low on charge or the
cap tube plugged?”
Answer: “No.”
Question: “Why not?”
Answer: “Because, if it were low on charge or if the
cap tube was even partially plugged, the low
side would be starved for refrigerant and
therefore, the suction line would be warm.
Also, the compressor housing would be
hot.”
Question: “Then why isn’t it cooling properly?”
Answer: “Because the evaporator is not picking up
the heat load.”
Question: “What could cause the evaporator to not
pick up the heat load?”
Answer: (possible causes and repairs)
1. “The filter could be dirty.”
This is the most probable cause and, of course, the
easiest to check and correct.
2. “The ceiling assembly louvers could be completely
closed.”
This problem is easy to find and it is usually corrected
by opening the discharge louvers.
3. “The fan could be at fault.”
A mechanical problem such as the wheel (squirrel
cage) loose on the shaft is usually rather obvious.
Checking why a fan motor does not come up to speed
is a little more involved.
A) Seized bearings – This does not often occur;
but if it does, a few drops of oil will usually
free them temporarily. If the shaft is scored
in the bearings, it will soon tighten up again.
Now is the time to replace the motor.
b) Partially burned motor windings – See fan
motor check procedure.
c) Shorted or open capacitor – See capacitor
test.
4. “The evaporator coil face could be coated with lint,
dirt, etc.
Dirt or lint on the coil will restrict the flow of air
through the coil and the unit must be removed from
the recreational vehicle and the soil must be
thoroughly cleaned with strong detergent (Coil X,
Calclean, etc.) and water. Be sure to protect the fan
motor and electrical controls during cleaning by
covering them with polyethylene sheet. After the
system is cleaned, allow it to thoroughly dry for
several hours (before turning it on) to prevent
electrical shorts.
Before system is put back into operation, be sure the
filter is properly installed to prevent recurrence of
dirty coil.
Problem
3. No compressor (Does not try to start).
The customer turns the selector switch to “Cool” and the
thermostat to a low temperature (below room temperature).
The fan runs OK, but the unit does not cool. When the unit
housing is removed, we observe that the compressor does not
run and it does not hum (the compressor is completely dead).
Question: “What are the possible causes?”