How to Test a Trane Capacitor

Heating and air conditioning capacitors store electrical energy to allow high voltage discharge or to smooth the incoming electricity. Capacitors collect and store electrical energy in two plates until the electricity is needed by the electrical system. An insulator, typically a dielectric gel or ceramic plate, separates the plates, preventing the electricity from arcing, discharging or leaking the stored electricity. Replace your Trane device's capacitors if they have visibly failed, such as leaks, corrosion or bulging, or if a resistance test demonstrates the capacitor has internally failed.

Discharge capacitors before servicing to avoid electric shock.
  1. Turn off the Trane device. Unplug the device from the electrical socket, turn off the switch at the circuit breaker, or pull the fuse from the fuse box. Unscrew or unbolt the device housing to expose the electrical circuit board. Find the capacitor to be tested.

  2. Examine the capacitor for visible failure. Bulging capacitors indicate internal failure. Capacitors with broken sides, leaks or large amounts of corrosion have failed. Corroded leads alone do not indicate part failure. Small amounts of corrosion or rust on the metal leads protruding from the capacitor is normal, especially on capacitors exposed to wet or humid conditions. Test the resistance of the capacitor with corroded leads, before replacing.

  3. Locate the two metal wires, or leads, protruding from each edge or from the bottom of the capacitor.

  4. Hold a metal screwdriver by the insulated plastic handle to prevent electric shock. Press the metal portion of the screwdriver against the capacitor leads for 30 seconds or more. The metal shaft of the screwdriver provides resistance to the electrical charge crossing between the leads. The resistance of the metal screwdriver shaft drains the capacitor charge. If necessary, use an insulated heavy gauge wire with an exposed metal end to drain the capacitor charge. As with the metal screwdriver, only hold the wire by the insulated covering.

  5. Set the multimeter to measure resistance, or "Ohms." Press the red multimeter lead to one of the capacitor leads. Press the remaining multimeter lead to the remaining capacitor lead. Monitor the output on the multimeter. The multimeter will slowly charge a functioning capacitor through the battery power supplied by the multimeter leads.

  6. Measure the capacitor's ability to collect and store energy as an electrical charge. Capacitors failing to store a charge will display a "zero" reading on the multimeter output. Capacitors in an "open" state will fail to produce any reading on the multimeter. Capacitors with leaking charges will initially start at zero, climb toward infinity, but stop the climb as the charge begins to leak. Fully functioning capacitors will read zero initially and steadily climb toward infinity.

  7. Replace any capacitors failing the resistance test.


  • Some capacitors contain sufficient electrical charge to cause bodily harm. Do not handle the capacitor prior to discharging the electricity stored within the capacitor.
  • Use a rubberized insulated glove to handle the screwdriver or wire for added safety.
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