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Choosing a replacement run capacitor: match the microfarads, voltage equal or higher, dual vs single, and what not to substitute

A run capacitor replacement should match the original microfarad (uF/MFD) rating; Regal (motor maker) and Supplyhouse call for staying within about plus or minus 6%, warning that a capacitor more than 6% low cuts torque and overheats the windings. One trade article accepts plus or minus 10% in a pinch; use the stricter number. The voltage rating may be equal or higher (440 V can replace 370 V), never lower. A dual capacitor (for example 35/5 or 45/5: compressor/fan) must match both values and have HERM, FAN and C terminals; two singles of the right values can stand in where space allows. Never use a start capacitor as a run capacitor.

Cross-checked ~20 min easyBrands: All

Before you start

  • Kill power at the disconnect and breaker, verify dead, then discharge the capacitor before touching terminals (see discharge-a-capacitor-safely).
  • Sealed-system work (compressor replacement, refrigerant) is EPA 608 certified-tech work; a capacitor swap does not open the system.

Diagnostic steps

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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

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Choosing a replacement run capacitor: match the microfarads, voltage equal or higher, dual vs single, and what not to substitute · OnCall Tech