Service Manual

SERVICING
41
S-18 TESTING CRANKCASE HEATER
(OPTIONAL ITEM)
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 accumu-
lation 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.
S-21 CHECKING REVERSING VALVE AND SO-
LENOID
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 connect-
ing 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 and PCBDM160 defrost controls have
a three (3) minute compressor off cycle delay.
NOTE: The PCBDM133 and PCBDM160 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 and PCBDM160) 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 and PCBDM160). 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 and PCBDM160) & "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
returning system to service.
S-25 TESTING DEFROST THERMOSTAT
1. Install a thermocouple type temperature test lead on the
tube adjacent to the defrost control. Insulate the lead
point of contact.
2. Check the temperature at which the control closes its
contacts by lowering the temperature of the control. The
defrost control should close at 34°F ± 5°F.
3. Check the temperature at which the control opens its
contacts by raising the temperature of the control. The
defrost control should open at 60°F ± 5°F.
4. If not as above, replace control.