Therma-Stor Ultra Aire XT105H, Owner'S Manual

Page: 13 / 20

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.
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.
If sludge is evident in the discharge line, it will likely be found in
the suction line. This indicates the compressor burned out while
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.
13
Ultra-Aire XT105H, XT155H, and XT205H Installer’s & Owner’s Manual