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SERVICING
Testing crankcase heater
NOTE: Not all compressors use crankcase heaters.
The crankcase heater must be energized a minimum of
four (4) hours before the condensing unit is operated.
Crankcase heaters are used to prevent migration or
accumulation of refrigerant in the compressor crankcase
during the off cycles and prevents liquid slugging or oil
pumping on start up.
A crankcase heater will not prevent compressor damage
due to a floodback or over charge condition.
Disconnect ALL power before servicing.
1. Disconnect the heater lead in wires.
2. Using an ohmmeter, check heater continuity - should
test continuous. If not, replace.
Checking Crankcase Heater Thermostat
NOTE: Not all models with crankcase heaters will have
a crankcase heater thermostat.
1. Install a thermocouple type temperature test lead on
the discharge line adjacent to the crankcase heater
thermostat.
2. Check the temperature at which the control closes its
contacts by lowering the temperature of the control.
The crankcase heater thermostat should close at
67°F ± 5°F.
3. Check the temperature at which the control opens
its contacts by raising the temperature of the control.
The crankcase heater thermostat should open at
85°F ± 5°F.
4. If not as above, replace control.
Checking Reversing Valve And Solenoid
Reversing valve used in heat pumps could potentially leak
internally. Discharge gases can leak into the suction inside
the valve. Compound gages will give the same symptoms
as bad compressor valves or broken scroll flanks. The
temperature between true suction and the suction line after
the valve should not be greater than 4 degrees. Note: The
center tube is always the suction line and should be cold.
Troubleshooting the Reversing Valve for Electri-
cal Failure
1. Place unit into the cooling mode. Test for 24 volts at
the solenoid. If there is no voltage present at coil,
check the control voltage.
WARNING
2. If voltage is present, loosen the nut on the top of
the coil. Remove the coil, there should be slight
resistance.
3. If the slight resistance is felt, remove the coil. As you
remove the coil listen carefully, an audible click should
be detected. The clicking is due to the movement
of the pilot valve plunger. The absence of a clicking
sound indicates the plunger is stuck.
Troubleshooting Mechanical Failures on a Revers-
ing Valve by Pressure
1. Troubleshooting the reversing valve can be done by
pressure and touch.
2. Raise the head pressure. In the cooling mode block
the fan exhaust. Once head pressure has been
raised, cycle between cooling and heating and see if
the piston can be freed.
Troubleshooting Mechanical Failures on a Revers-
ing Valve byTemperature
1. When operating properly the valve contains refrigerant
gases at certain temperatures.
2. The discharge line should be the same temperature
after the valves discharge line.
3. The true suction should be the same as the suction
line after the valve. If there is a 4-degree difference,
valve is leaking
When stuck in the mid-position, part of the discharge gas
from the compressor is directed back to the suction side,
resulting in excessively high suction pressure. An increase
in the suction line temperature through the reversing
valve can also be measured. Check operation of the valve
by starting the system and switching the operation from
COOLING to HEATING cycle.
If the valve fails to change its position, test the voltage
(24V) at the valve coil terminals, while the system is on the
COOLING cycle.
If voltage is registered at the coil, tap the valve body lightly
while switching the system from HEATING to COOLING,
etc. If this fails to cause the valve to switch positions,
remove the coil connector cap and test the continuity of
the reversing valve solenoid coil. If the coil does not test
continuous - replace it. If the coil test continuous and 24
volts is present at the coil terminals, the valve is inoperative
- replace it.
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