THE INDUSTRY LEADER SINCE 2006
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Troubleshoot a Capacitor

Troubleshoot a Capacitor

How to measure the capacitance with standard run and dual run capacitors.

First, let's determine the difference between a run and a dual run capacitor.

The capacitor on the left is a "dual run round" and the capacitor on the right is a "run oval".

Round vs oval capacitors

How to determine the terminals on a dual run capacitor.

The is the top of a dual run capacitor and if you look real close you can see the "c", "herm", and "fan" terminals.  Another way to know the terminal types is to count the number of connections that are located on each terminal.  This is common on most dual capacitors.   The fan has 2 connection points, herm or compressor has 3, and the common or c has 4.

Run Capacitor Terminals

How to measure the capacitance for a run capacitor.

Here is how to verify a run capacitor using a standard multimeter with a MFD option.  Just place the probes on both terminals. In this case the reading is 7.7uf/mfd.  The rating is 7.5uf/mfd.  This is normal and validates the capacitor.

Oval Capacitor Test

How to measure the capacitance for a dual run capacitor.

Here is how to verify a dual run capacitor using a stanadard multimeter with a MFD option.  Just place one of the probes on either the herm or fan terminal (depending on what you are checking) and the other probe on the common terminal.  In this case the reading is 43.8uf/mfd.  The rating is 45uf/mfd for the herm terminal.  You can then check the fan by moving the probe from the herm to the fan terminal and leave the second probe on the common terminal.

Round Capacitor Testing

 

This guide's intention is to provide an understanding of the operation of a furnace. It is not intended as a hands-on teaching tool, or aide. All HVAC equipment should be serviced by a licensed HVAC technician. Consult your local, town, city, and state laws, ordinances, and regulations prior to accessing, engaging, troubleshooting, repairing, or servicing any HVAC equipment.

SAFETY NOTE - ALWAYS TURN THE MAIN POWER AND GAS VALVE OFF BEFORE SERVICING ANY HVAC EQUIPMENT.  SERIOUS INJURY CAN OCCUR.