A refrigeration compressor has failed to start. After verifying that the electrical circuit to the motor, including all switches and circuit breakers, is complete, the next item to check would likely be which?

• A. Lubrication oil level
• B. Belt tension
• C. Temperature and pressure controls
• D. Condenser water flow

Answer: (C)

When power to the motor is confirmed, the next likely cause for a compressor that won’t start is the safety controls in the start circuit—specifically the temperature and pressure controls. These devices monitor suction and discharge conditions and will electrically block the starting relay if conditions are outside safe limits. For example, a low-pressure switch can prevent starting if suction pressure is too low (sometimes due to low refrigerant, evaporator frost, or a charge issue), while a high-pressure switch can prevent starting if condenser pressure is too high. If either control is stuck open or out of spec, the compressor won’t start even though the electrical path to the motor is good. Lubrication oil level and belt tension matter for operation, but they’re less likely to stop a motor from starting once power is present; condenser water flow affects operating conditions but the immediate gating factor after power verification is the temperature and pressure controls.