Most common motor failures are due to either an open, grounded, or short circuit. Directions below are specifically for
OPEN CIRCUIT
To determine if any winding has a break in the internal wires and current is unable to pass through:
1.Be sure all power is off.
2.Discharge all capacitors.
3.Remove wires from terminals C, S and R.
4.Check resistance from
Because winding resistances are usually less than 10 ohms, each reading appears to be approximately 0 ohm. If resistance remains at 1000 ohms, an open or break exists, and compressor should be replaced.
CAUTION: Be sure internal
GROUND CIRCUIT
To determine if a wire has broken or come in direct contact with shell, causing a direct short to ground:
1.Be sure all power is off.
2.Discharge all capacitors.
3.Remove wires from terminals C, S, and R.
4.On hermetic compressors, allow crankcase heaters to re- main on for several hours before checking motor to ensure windings are not saturated with refrigerant.
5.Use an ohmmeter on R X 10,000 ohm scale. A megohm- meter may be used in place of ohmmeter. Follow manufac- turer’s instructions.
6.Place 1 meter probe on ground or on compressor shell. Make a good
7.Note meter scale.
8.If reading of zero or low resistance is obtained, motor is grounded. Replace compressor.
A 1 ton or less capacity compressor is probably grounded if resistance is below 1 million ohms. On
Example:
230 volts X 1000 ohms/volt = 230,000 ohms minimum.
SHORT CIRCUIT
To determine if any wires within windings have broken through their insulation and made contact with other wires, thereby shorting all or part of the winding(s), be sure the following conditions are met:
1.Correct
2.Temperature of windings must be as specified, usually about 70°F.
3.
4.Motor must be dry or free from direct contact with liquid refrigerant.
MAKE THIS CRITICAL TEST
(Not advisable unless above conditions are met.)
1.Be sure all power is off.
2.Discharge all capacitors.
3.Remove wires from terminals C, S, and R.
4.Place instrument probes together and determine probe and lead wire resistance.
5.Check resistance readings from
6.Subtract instrument probe and lead resistance from each reading.
If any reading is within ± 20 percent of known resistance, motor is probably normal. Usually a considerable difference in reading is noted if a
III. SYSTEM CLEANUP AFTER BURNOUT
CAUTION: Turn off all power to unit before proceed- ing. Wear safety glasses and gloves when handling refrigerants. Acids formed as a result of motor burnout can cause burns.
NOTE: To analyze level of suspected contamination from com- pressor burnout, use Total Test. See your distributor/branch.
Some compressor electrical failures can cause motor to overheat. When this occurs,
In mild burnout, there is little or no detectable odor. Compressor oil is clear or slightly discolored. An acid test of compressor oil will be negative. This type of failure is treated the same as mechanical failure.
In a severe burnout, there is a strong, pungent,
IV. COMPRESSOR REMOVAL AND REPLACEMENT
Once it is determined that compressor has failed and the reason established, compressor must be replaced.
CAUTION: Wear safety glasses and gloves when han- dling refrigerants and when using brazing torch.
1.Shut off all power to unit.
2.Remove and recover all refrigerant from system until pressure gages read zero psi. Use all service ports.
3.Disconnect electrical leads from compressor. Disconnect or remove crankcase heater and remove
4.Cut compressor from system with tubing cutters. Do not use brazing torch for compressor removal. Oil vapor may ignite when compressor is disconnected.