Keeping Your HVAC System In Great Condition

How To Locate And Test The Capacitors In Your Air Conditioner And Furnace

10 November 2016

Herbert Franklin

Capacitors are small electricity storage devices that can help your HVAC unit with a boost at startup or while running to prevent unexpected shutdowns due to power interruptions. Capacitors come in either the start capacitor or run capacitor variety and separate capacitor sets can exist in both your air conditioner and your furnace.

If your air conditioner or furnace has suddenly ceased starting up or shuts down too quickly after starting, there might be a problem with a capacitor in the affected unit. You can test the capacitors in either the air conditioner or furnace using a multimeter. If you don't feel comfortable performing the test, call in an air conditioning maintenance company.

What You Need:

• Owner's manual, optional
• Screwdriver
• Multimeter
• Insulted screwdriver

Step 1: Locate the Capacitor

Turn off the power to your air conditioner or furnace at the circuit breaker before working on the capacitors; note that the capacitors will still store electricity until you drain the charge.

Consult your owner's manual for the air conditioner or furnace for the quickest route to the capacitor in your unit. The following offers general instructions for locating capacitors.

In an air conditioner, use a screwdriver to remove the screws holding on the access panel. Remove the panel and set it aside with the screws. Look inside the opened access area and you should see a cylindrical part or parts with wires attached. Those are the capacitors.

In a furnace, twist the knobs on the upper access panel to loosen then remove the panel and set it aside. Look at the bottom frame of where the panel was attached and you should see the screws holding the lower panel door in place. Use a screwdriver to remove those screws then set the lower panel and its fasteners aside. Look inside the opened lower access area and you should see the capacitor or capacitors.

Step 2: Drain and Remove the AC or Furnace Capacitors

Drain the start capacitor on either the air conditioner or the furnace by carefully unhooking the wires attached to the capacitor then hooking the multimeter probes up to the now open terminals. Turn the meter to AC and wait until the reading drops to nothing. You can then unhook the probes and continue on to Step 3.

Drain the run capacitor on either unit by laying the end of an insulated screwdriver across the terminals – carefully avoiding touching the metal of the driver! Hold the tool in place for several moments then double check that the charge is gone using the AC method used for the start capacitor.

Remove capacitors by unscrewing the mounting screws and pulling the part up and out of the system. Lay the capacitor on a flat worktable to perform the testing.

Step 3: Test the Run or Start Capacitor

Both types of capacitors from either unit test the same way. Turn the meter to Ohms of resistance setting, hook the probes up to the terminals of your tester capacitor, and watch for the reading. If the reading matches the required range printed on the cylinder, the part is healthy. If the reading doesn't match, or the meter reading jumps around erratically, the capacitor needs replacing.

If the capacitor was healthy, call in an HVAC technician to diagnose what else could cause your air conditioner or furnace issues.

Share