SERVICING
19
With power ON:
WARNING
Line voltage now present.
1. Check the serial data plate for the compressor locked
rotor amps (LRA) rating.
2. Using an ampmeter, measure the amperage reading
for the run and common wires to the compressor.
Since the compressor motor overload will likely
trip soon after drawing locked rotor amps, this
measurement should be taken as soon as the
compressor starts.
3. If the amperage reading roughly equals the
compressor LRA rating and all other checks have
been completed, locked rotor amps has been
verified.
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.
WARNING
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
Occasionally the reversing valve may stick in the heating or
cooling position or in the mid-position.
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 no voltage is registered at the coil terminals, check
the operation of the thermostat and the continuity of the
connecting wiring from the “O” terminal of the thermostat to
the unit.
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.
Testing Defrost Control
NOTE: PCBDM133 defrost control has a three (3)
minute compressor off cycle delay.
NOTE: The PCBDM133 defrost control is shipped from
the factory with the compressor delay option selected.
This will de-energize the compressor contactor for 30
seconds on defrost initiation and defrost termination.
If the jumper is set to Normal, the compressor will
continue to run during defrost initiation and defrost
termination. The control will also ignore the low
pressure switch connected to R-PS1 and PS2 for 5
minutes upon defrost initiation and 5 minutes after
defrost termination.
To check the defrost control for proper sequencing,
proceed as follows: With power ON; unit not running.
1. Jumper defrost thermostat by placing a jumper wire
across the terminals “DFT” and “R”/” R-DFT” at
defrost control board.
2. Remove jumper from timer pins and jump across test
pins on defrost control board.
NOTE: Do not use
screwdriver or field supplied jumper to test the
control.
3. Set thermostat to call for heating. System should go
into defrost within 21 seconds.
