8. Compressor terminal C and compressor case:
Continuity indicates a grounded motor; the
compressor must be replaced.
9. Disconnect the wires from the capacitor. Set the
ohmmeter to the Rx1 scale; the capacitor is shorted
and must be replaced if continuity exists across its
terminals. If there is no needle movement with the
meter set on the Rx100000 scale, the capacitor is
open and must be replaced.
10. Reconnect the wires to the compressor and
capacitor; plug in and turn on the unit. If the
compressor fails to start, replace the run capacitor.
11. If the unit still does not start, adding a hard-start kit
will provide greater starting torque. If this does not
work, the compressor has an internal mechanical
defect and must be replaced.
5.6B Replacing a Burned Out Compressor
The refrigerant and oil mixture in a compressor
is chemically very stable under normal operating
conditions. However, when an electrical short occurs in
the compressor motor, the resulting high temperature
arc causes a portion of the refrigerant oil mixture to
break down into carbonaceous sludge, a very corrosive
acid, and water. These contaminants must be carefully
removed otherwise even small residues will attack
replacement compressor motors and cause failures.
The following procedure is effective only if the system is
monitored after replacing the compressor to insure that
the clean up was complete.
1. This procedure assumes that the previously listed
compressor motor circuit tests revealed a shorted or
open winding. If so, cautiously smell the refrigerant
from the compressor service port for the acid odor of
a burn out.
WARNING: The gas could be toxic and highly acidic. If no
acid odor is present, skip down to the section on changing
a non-burn out compressor.
2. Remove and properly dispose of the system charge.
DO NOT vent the refrigerant or allow it to contact your
eyes or skin.
3. Remove the burned out compressor. Use rubber
gloves if there is any possibility of coming in contact
with the oil or sludge.
4. To facilitate subsequent steps, determine the type of
burn out that occurred. If the discharge line shows
no evidence of sludge and the suction line is also
clean or perhaps has some light carbon deposits,
the burn out occurred while the compressor was not
rotating. Contaminants are therefore largely confined
to the compressor housing. A single installation of
liquid and suction line filter/driers will probably clean
up the system.
If sludge is evident in the discharge line, it will
likely be found in the suction line; this indicates the
compressor burned out will running. Sludge and acid
have been pumped throughout the system. Several
changes of the liquid and suction filter/driers will
probably be necessary to cleanse the system.
5. Correct the system fault that caused the burn out.
Consult the factory for advice.
6. Install the replacement compressor with a new
capacitor and an oversized liquid line filter.
In a running burn out, install an oversized suction line
filter/drier between the accumulator and compressor.
Thoroughly flush the accumulator with refrigerant to
remove all trapped sludge and to prevent the oil hole
from becoming plugged. A standing burn out does
not require a suction line filter/drier.
7. Evacuate the system with a good vacuum pump and
accurate vacuum gauge. Leave the pump on the
system for at least an hour.
8. Operate the system for a short period of time,
monitoring the suction pressure to determine that
the suction filter is not becoming plugged. Replace
the suction filter/drier if pressure drop occurs. If a
severe running burn out has occurred, several filter/
driers may have to be replaced to remove all of the
acid and moisture.
NOTE: NEVER use the compressor to evacuate the system
or any part of it.
5.6C Replacing a Compressor- Non-Burn Out
Remove the refrigerant from the system. Replace the
compressor and liquid line filter/drier. Charge the system
to 50 PSIG and check for leaks. Remove the charge and
weigh in the refrigerant quantity listed on the nameplate.
Operate the system to verify performance.
5.7 Relay
The contacts of the single pole, single throw relay
complete the power circuit to the compressor. The
contacts are closed when power is provided to the relay
coil via the control circuit. The control circuit includes the
humidity control, defrost thermostat and timer.
5.8 Humidity Control
The humidity control is an adjustable switch that closes
when the relative humidity of the air in which it is located
rises to the dial set point. It opens when the RH drops 4
to 6% below the set point.
6
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