FieldBench
Procedures
Electrical4 min

Capacitor test

Dual and single run capacitors. Most ‘dead condensing units’ are still a weak cap.

Safety

  • Kill power and confirm 0 VAC at the capacitor. Short HERM-C and FAN-C with an insulated screwdriver to dump residual.
  • A bulged or leaking can is failed — replace, do not measure.

Measure

  • Meter on µF. HERM to C is the compressor winding. FAN to C is the outdoor fan. HERM to FAN should be roughly the sum.
  • Replace at ±6% of nameplate (or OEM spec). A cap that ‘runs’ at −15% cooks the compressor.
  • Match µF and equal or greater VAC. Dual can: both values and the same lug layout.

While you are there

  • Check contactor face for pitting and voltage drop under load (see the contactor guide).
  • Spin the fan by hand with power off. Tight bearings plus a weak cap is a repeat call.