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DRY
150 Installation, Operation and Maintenance Instructions
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7.6A Checking Compressor Motor Circuits
Perform the following tests if the impeller fan runs but the compressor does not with the fan switch and
ventilation timer OFF and the humidity control ON.
1. Unplug the unit; remove the cabinet side and the electrical connection cover on the compressor top.
2. Plug in the unit and turn the humidity control to ON. Check for 110 volts from compressor terminal R
to overload terminal 3 using an AC voltmeter. If voltage is present, go to step 3. If no voltage, there may
be a loose connection in the compressor circuit. Test each component for continuity. See the appropriate
section if a defect is suspected.
3. Unplug the unit, and then disconnect the red and yellow wires from compressor terminals R & S. Using
an ohmmeter check continuity between the points listed below.
4. Compressor terminals C and S: No continuity indicates an open start winding. The compressor must be
replaced. Normal start winding resistance is 3 to 7 ohms.
5. Compressor terminals C and R: No continuity indicates an open run winding. The compressor must be
replaced. Normal run winding resistance is .5 to 2 ohms.
6. Compressor terminal C and overload terminal 1: No continuity indicates a defective overload lead.
7. Overload terminals 1 and 3: If there is no continuity, the overload may be tripped. Wait 10 minutes and
try again. If there is still no continuity, it is defective and must be replaced.
8. Compressor terminal C and compressor case: Continuity indicates a grounded motor. The compressor
must be replaced.
9. Disconnect the wires from the run 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 (relay & capacitor) will provide greater starting
torque. If this doesn't work, the compressor has an internal mechanical defect and must be replaced.
7.6B 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.
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 contacting 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.
FOR HVAC INSTALLER ONLY
