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SERVICING
S-18 TESTING CRANKCASE HEATER
(OPTIONAL ITEM)
Note: Not all compressors use crankcase heaters.
The crankcase heater must be energized a minimum of twenty-
four (24) hours before the compressor is operated.
Crankcase heaters are used to prevent migration or accumula-
tion of refrigerant in the compressor crankcase during the off
cycles and prevents liquid slugging or oil pumping on start up.
On some models, the crankcase heater is controlled by a crank-
case heater thermostat that is wired in series with the crank-
case heater.
A crankcase heater will not prevent compressor damage due
to a floodback or over charge condition.
WARNING
DISCONNECT POWER SUPPLY BEFORE SERVICING.
1. Disconnect the heater lead wires.
2. Using an ohmmeter, check heater continuity - should test
continuous, if not, replace.
S-18A 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 thermo-
stat.
2. Check the temperature at which the control closes its con-
tacts by lowering the temperature of the control. The crank-
case heater thermostat should close at 67°F ± 5°F.
3. Check the temperature at which the control opens its con-
tacts by raising the temperature of the control. The crank-
case heater thermostat should open at 85°F ± 5°F.
4. If not as above, replace control.
S-21 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 suc-
tion line temperature through the reversing valve can also be
measured. Check operation of the valve by starting the sys-
tem 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 op-
eration 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.
S-24 TESTING DEFROST CONTROL
NOTE: PCBDM133 defrost controls have a three (3) minute
compressor off cycle delay.
NOTE: The PCBDM133 defrost controls are 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" on PCBDM133) at
defrost control board.
2. Connect jumper across test pins on defrost control board.
3. Set thermostat to call for heating. System should go into
defrost within 21 seconds.
4. Immediately remove jumper from test pins.
5. Using VOM check for voltage across terminals "C & O"
("O-RV" on PCBDM133). Meter should read 24 volts.
6. Using VOM check for voltage across fan terminals DF1
and DF2 on the board. You should read line voltage (208-
230 VAC) indicating the relay is open in the defrost mode.
7. Using VOM check for voltage across "W2" (W on
PCBDM133) & "C" terminals on the board. You should read
24 volts.
8. If not as above, replace control board.
9. Set thermostat to off position and disconnect power before
removing any jumpers or wires.
NOTE: Remove jumper across defrost thermostat before re-
turning system to service.
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