When diagnosing a compressor that won't start, which step best aligns with a proper starting-issue checklist?

When diagnosing a compressor that won't start, which step best aligns with a proper starting-issue checklist?

• A. Replace the compressor immediately.
• B. Verify main power at disconnect and breaker; inspect contactor coil and wiring; check overload and fuses; test start capacitor/relay; check safety switches; verify refrigerant charge and pressures; inspect for miswired components.
• C. Increase system charge to maximum.
• D. Disconnect all wiring and attempt to restart.

Answer: (B)

Diagnosing a compressor that won’t start relies on a systematic electrical and control-system check, not on guessing or jumping straight to replacement. Start by confirming there is power where it should be—at the disconnect and the main breaker—and then look at the control path: inspect the contactor coil and its wiring to ensure the relay is pulling in as it should. Next, check the overload protector and any fuses to rule out an opened protection device. Test the start capacitor and relay, since a faulty capacitor or relay can prevent the motor from starting even if power is present. Also verify safety switches and interlocks (like pressure or door switches) that might deliberately keep the compressor from engaging. Don’t overlook refrigerant-related factors—low charge or abnormal pressures can trigger protective controls that stop startup. Finally, inspect the wiring for miswirings or loose connections that can interrupt the start sequence. This approach targets the common causes in the start circuit and reduces unnecessary replacement. Replacing the compressor immediately skips diagnosing these potential electrical or control faults. Increasing system charge is not a fix for a starting issue and can lead to further problems. Disconnecting all wiring as a step is unsafe and uninformative for diagnosing why the compressor won’t start.

Diagnosing a compressor that won’t start relies on a systematic electrical and control-system check, not on guessing or jumping straight to replacement. Start by confirming there is power where it should be—at the disconnect and the main breaker—and then look at the control path: inspect the contactor coil and its wiring to ensure the relay is pulling in as it should. Next, check the overload protector and any fuses to rule out an opened protection device. Test the start capacitor and relay, since a faulty capacitor or relay can prevent the motor from starting even if power is present. Also verify safety switches and interlocks (like pressure or door switches) that might deliberately keep the compressor from engaging. Don’t overlook refrigerant-related factors—low charge or abnormal pressures can trigger protective controls that stop startup. Finally, inspect the wiring for miswirings or loose connections that can interrupt the start sequence. This approach targets the common causes in the start circuit and reduces unnecessary replacement.

Replacing the compressor immediately skips diagnosing these potential electrical or control faults. Increasing system charge is not a fix for a starting issue and can lead to further problems. Disconnecting all wiring as a step is unsafe and uninformative for diagnosing why the compressor won’t start.