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SERVICING
24
A. If the compressor starts and continues to run, the
cause for failure is somewhere else in the sys-
tem.
B. If the compressor fails to start - replace.
Locked Rotor Test
If fuse, circuit breaker, ground fault protective device, etc.
has tripped, this is a strong indication that an electrical
problem exists and must be found and corrected. The
circuit protective device rating must be checked and its
maximum rating should coincide with that marked on the
equipment nameplate.
Before checking for locked rotor, the compressor terminals
should be checked for open windings (see Resistance Test)
and the run capacitor and start capacitor (if used) should
be checked thoroughly (see Checking Capacitor).
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 (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
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 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.
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,