Refrigeration & Air Conditioning Mechanic Red Seal · Question
An electrician is troubleshooting a single-phase compressor motor that hums but does not start. Using an ohmmeter, the resistance across the run winding is measured at 2.5 ohms, and across the start winding at 4.0 ohms. The resistance across the common and run terminals is 2.5 ohms, and across common and start terminals is 4.0 ohms. What is the most probable issue, assuming the power supply is present?
The resistance readings indicate the run and start windings are intact and appropriately proportioned for a single-phase motor. The motor hums but doesn't start
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Question: An electrician is troubleshooting a single-phase compressor motor that hums but does not start. Using an ohmmeter, the resistance across the run winding is measured at 2.5 ohms, and across the start winding at 4.0 ohms. The resistance across the common and run terminals is 2.5 ohms, and across common and start terminals is 4.0 ohms. What is the most probable issue, assuming the power supply is present?
Answer options: ✅ A faulty starting capacitor.
- An open run winding.
- A shorted start winding.
- A grounded motor winding.
Correct answer: A faulty starting capacitor.
Explanation: The resistance readings indicate the run and start windings are intact and appropriately proportioned for a single-phase motor. The motor hums but doesn't start suggests an issue with the starting circuit, most commonly the start capacitor or centrifugal switch/relay, preventing the required phase shift for initial rotation.
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