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How to test a capacitor with a multimeter

  • Takes about 10 minutes
  • Some experience needed
  • 2 tools needed
  • Updated

A capacitor fails gradually, so "it looks fine" proves nothing — the only verdict that counts is a microfarad reading against the number stamped on the can.

A tech hasn't checked this guide yet

Everything below is written from the field, but it has not been through one of our licensed techs — so we are keeping it out of search until it has. Read it, use your own judgement, and if something here does not match the unit in front of you, trust the unit.

Reviewed by a licensed tech: not yet

Data points: 4 of 2 needed — 3 written steps, 1 part bound to the fix, 2 tools listed, 1 related model, symptom and guide links

Browse our reviewed guides →

Safety — critical

Pull the disconnect at the condenser AND kill the breaker, then discharge the capacitor across a 20 kΩ / 2 W resistor before you touch a terminal. A run capacitor stores a lethal charge with the power off and holds it for hours — a screwdriver across the terminals will discharge it, damage it, and put an arc flash in your face. Use the resistor.

What you'll need

  • Multimeter with a capacitance (µF) range

    A meter without one cannot do this test. Continuity mode is not a substitute.

  • 20 kΩ / 2 W resistor with insulated leads

    The discharge tool.

The fix, step by step

  1. Isolate and discharge

    Disconnect pulled, breaker off, then discharge across HERM–C and FAN–C with the resistor. Do not skip to step 2 because the power is off — the power being off is precisely when a capacitor is dangerous.

  2. Pull one lead off and read µF

    The capacitor has to be out of circuit or the meter reads the motor windings along with it. Lift the spades, set the meter to its µF range, and read HERM to C, then FAN to C.

  3. Compare against the stamp, with the tolerance

    The can is rated ±6%. A 45 µF section reading 42.3 or better is alive; 40.1 is failed even though it still "reads". A section reading zero or open is obviously gone. Both sections are tested separately — one half of a dual can fails on its own all the time.

Who wrote this

Written by Priya Raman SupplyAisle technical writer

Not yet reviewed by a licensed tech This one is still in the queue. It is written from the field, but until one of our techs has signed it off we would rather say so — and we are keeping it out of search until they do.

Updated first published