How To Disassemble Your AC’s Condensing Unit For Quick Troubleshooting Of The Capacitors And Contactor

Inefficient cooling can result from a variety of different problems with a central air conditioning system. If you want to diagnose the issue yourself, you might need to check several different parts for functionality or signs of damage to narrow down the problem's origin. A good place to start is in the condensing unit – or the part of your system that sits outside the house.

A condensing unit contains a number of parts, including start and run capacitors and the contactor. These are some of the best parts to check first if your unit either isn't starting at all or is cycling on and off too quickly, since a failure in these parts means the compressor won't turn on properly.

Consult your owner's manual ahead of the project if you need help locating the parts and to ensure your specific model doesn't have a slight variation on these directions.

What You Need:

  • Insulated screwdriver
  • Multi-meter
  • Camera

Step 1: Cutting Power and Gaining Access

Locate the fuse box near your condensing unit and completely pull out the fuse to cut power to the unit. If you don't see a fuse box, turn the power off at the main circuit breaker in your house.

Now you need to gain access to the parts you will check. Disassembling your condensing unit cover can vary depending on the model. Locate the fasteners that keep the access panel or condensing cover in place and remove the fasteners with a screwdriver. Place the screws and panel door or cover somewhere safe but accessible.

Step 2: Draining and Testing Capacitors

Locate the capacitors first as these store electricity even when the power is turned off in the unit. Unhook the wires from both capacitors to leave empty terminals behind.

Place the metal tip of the insulated screwdriver across the terminals on the run capacitor and hold it there for a few moments to drain out the charge. You can test to see that it is fully drained by turning your multi-meter to the ohms setting, hooking the multi-meter probes up to the capacitor terminals, and then checking that the reading says zero. If there's still a charge, put the screwdriver back on for a few more minutes and check again.

Don't use the screwdriver to drain the start capacitor. Turn your multi-meter to the AC setting and hook the probes up the start capacitor's terminals. Wait for the number to lower to zero.

Now you can test the capacitors. Set the multi-meter back to ohms and you will again attach the probes to the terminals of a capacitor. Each capacitor has the appropriate range of ohms printed on the side so you just need to make sure the reading matches the range. If it doesn't, you need a new capacitor.

Step 3: Test the Contactor

Test the contactor after the capacitors, because it's easy to accidentally bump the run capacitor while working on the contactor, so you don't want any electricity in there.

The contactor has more wires than the capacitors, so you might want to take a picture of the wire setup with a digital camera before removing the wires. Once the wires are removed, you can test the contactor to see if it has grounded or become stuck open.

First, stick the multi-meter still set to ohms between the terminal and coils on the contactor and check the reading. Next, put the multi-meter probes across the terminal and coils and check the reading. Both of these readings should be around 20 ohms; if the number is vastly different, you likely need a new contactor.

Step 4: Schedule a Service Call and Reassemble the Unit

If you've found your problem, contact an air conditioning repair service for a replacement part. You can also schedule a service call if you can't find the problem.

Reassemble your unit by reversing the disassembly instructions. Hook the wires back to the contactor and capacitors then replace the access panel or cover and its fasteners. Finish by restoring the electricity