Electrical System | Section 6 |
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COMPRESSOR ELECTRICAL DIAGNOSTICS
The compressor will not start or will trip repeatedly on overload.
Check Resistance (Ohm) Values
NOTE: Compressor windings can have very low ohm values. Use a properly calibrated meter.
Perform the resistance test after the compressor cools. The compressor dome should be cool enough to touch (below 120°F/49°C) to assure that the overload is closed and the resistance readings will be accurate.
SINGLE PHASE COMPRESSORS
1.Disconnect power from the cuber and remove the wires from the compressor terminals.
2.The resistance values between C and S and between C and R, when added together, should equal the resistance value between S and R.
3.If the overload is open, there will be a resistance reading between S and R, and open readings between C and S and between C and R. Allow the compressor to cool, then check the readings again.
THREE PHASE COMPRESSORS
1.Disconnect power from the cuber and remove the wires from the compressor terminals.
2.The resistance values between L1 and L2, between L2 and L3, and between L3 and L1 should all be equal.
3.If the overload is open, there will be open readings between L1 and L2, between L2 and L3, and between L3 and L1. Allow the compressor to cool, then check the readings again.
Check Motor Windings to Ground
Check continuity between all three terminals and the compressor shell or copper refrigeration line. Scrape metal surface to get good contact. If continuity is present, the compressor windings are grounded and the compressor should be replaced.
Determine if the Compressor is Seized
Check the amp draw while the compressor is trying to start.
COMPRESSOR DRAWING LOCKED ROTOR
The two likely causes of this are:
•Defective starting component
•Mechanically seized compressor To determine which you have:
1.Install high and low side gauges.
2.Try to start the compressor.
3.Watch the pressures closely.
A.If the pressures do not move, the compressor is seized. Replace the compressor.
B.If the pressures move, the compressor is turning slowly and is not seized. Check the capacitors and start relay.
COMPRESSOR DRAWING HIGH AMPS
The continuous amperage draw on
Diagnosing Capacitors
•If the compressor attempts to start, or hums and trips the overload protector, check the starting components before replacing the compressor.
•Visual evidence of capacitor failure can include a bulged terminal end or a ruptured membrane. Do not assume a capacitor is good if no visual evidence is present.
•A good test is to install a known good substitute capacitor.
•Use a capacitor tester when checking a suspect capacitor. Clip the bleed resistor off the capacitor terminals before testing.
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