Common on single-phase scroll/recip residential compressors. Usually capacitor, contactor, or seized compressor.
1
Failed run / start capacitor
highCheckDischarge cap. Measure µF; compare to nameplate (±6%).
FixReplace dual-run cap (matching µF and ≥ rated voltage). Add hard-start kit if borderline.
ToolsCapacitance meter · Insulated screwdriver
SafetyCapacitors hold lethal charge. Short across terminals with 20kΩ resistor before touching.
2
Pitted / welded contactor
medCheckPull disconnect. Inspect contacts for pitting, burning. Check coil resistance.
FixReplace 24 V contactor with matching FLA rating. Never file pitted contacts.
ToolsMultimeter · Nut driver set
3
Locked rotor / mechanically seized
criticalCheckCheck winding resistance C–R, C–S, R–S. Compare to spec. Megger to ground (<0.5 MΩ = grounded).
FixTry hard-start kit once. If still locked or grounded, compressor is dead — quote replacement.
ToolsMultimeter · Megohmmeter (500V) · Clamp meter
SafetyLockout/tagout. Recover refrigerant before opening system.
4
Low line voltage / loose lugs
medCheckMeasure voltage at contactor load side under start attempt. Should not drop below 90% nameplate.
FixTighten lugs to torque spec, repair undersized service, contact utility if supply low.
ToolsMultimeter · Torque screwdriver
Safety
Pull the disconnect and lock out before opening HVAC equipment. Discharge dual-run capacitors before handling. Refrigerant recovery and brazing require EPA 608 certification and proper PPE.