SERVICING
S-18 TESTING CRANKCASE HEATER
Note: Not all compressors use crankcase heaters.
The crankcase heater must be energized a minimum of four
(4) 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. Scroll Compressors are not equipped with a crankcase heat- ers.
A crankcase heater will not prevent compressor damage due to a floodback or over charge condition.
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-21 CHECKING REVERSING VALVE AND SOLENOID
Occasionally the reversing valve may stick in the heating or cooling position or in the
When stuck in the
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
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" 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". 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 & 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.
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 con- tacts by lowering the temperature of the control. The de- frost control should close at 34°F ± 5°F.
3.Check the temperature at which the control opens its con- tacts by raising the temperature of the control. The defrost control should open at 60°F ± 5°F.
4.If not as above, replace control.
S-50 CHECKING HEATER LIMIT CONTROL(S)
(OPTIONAL ELECTRIC HEATERS)
Each individual heater element is protected with an automatic rest limit control connected in series with each element to prevent overheating of components in case of low airflow. This limit control will open its circuit at approximately 150°F. to 160°F and close at approximately 110°F.
DISCONNECT ELECTRICAL POWER SUPPLY.
1.Remove the wiring from the control terminals.
2.Using an ohmmeter test for continuity across the normally closed contacts. No reading indicates the control is open - replace if necessary. Make sure the limits are cool before testing.
IF FOUND OPEN - REPLACE - DO NOT WIRE AROUND.
S-52 CHECKING HEATER ELEMENTS
Optional electric heaters may be added, in the quantities shown in the spec sheet for each model unit, to provide electric resis- tance heating. Under no condition shall more heaters than the quantity shown be installed.
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