Fan runs but compressor does not start; no heating occurs.

Safety first: High voltage and stored energy in capacitors can be dangerous. Discharge capacitors properly before handling.

• Listen for compressor: If there is no hum or click when heat is demanded, suspect the contactor or control board.
• Inspect contactor: Check for burnt or pitted contacts and verify the coil is being energized. Replace if defective.
• Test capacitor: Use a capacitance meter to verify the compressor capacitor value. Replace if out of tolerance.
• Compressor test: A technician should check compressor winding resistance and megger insulation. Replace the compressor if windings are open or shorted.