Day 159-The Joy of Home Ownership

Air Conditioner Repair

Air Conditioner / October 22, 2016

Is your AC not working? If your central air conditioner is not cooling right, save money, time, and get comfortable again with these expert DIY air conditioning troubleshooting and repair techniques.

In brief:

If your AC is not working at all:

1. Be sure it is receiving power at the electrical panel.
2. Reset the equipment’s switches and/or overloads.
3. Check the thermostat settings.
4. Check the condensate overflow switch.

If your AC is not cooling but runs:

1. Turn off the power.
2. Clean or change the filter.
3. Look to see if ice has formed on the coils and, if it has, turn on the power and the fan to melt it.
4. Clean the condensate drain.
5. Finally, check and clean the outdoor compressor.

In depth:

Several different kinds of problems can occur with a central air-conditioning system. We discuss some of the most common ones below:

• AC not working at all
• AC not cooling well but runs
• Room temperature too hot or too cold
• Water leaks from air conditioner
• Air conditioner makes strange noises
• Air conditioner won’t turn off

Although a qualified air-conditioning repair person should handle certain types of central air conditioner repairs, you’ll find methods for handling simple repairs and maintenance yourself in this article.

In addition to the information below, see these two articles for the general care and maintenance of your air conditioner: Preparing Your Air Conditioner for Summer and How to Replace Furnace & AC Filters. Most noteworthy, you should replace the filters at least twice a year, before the heating and cooling seasons.

Central AC Not Working At All

If your central air conditioner won’t go on automatically when the thermostat signals the need for cooling:

1 and any secondary circuit panels for a tripped breaker or blown fuse. If you find the problem there, reset the breaker by turning it off and then on or replace the fuse. A central air conditioner typically connects to a dedicated 240-volt circuit.

If the breaker continues to trip, suspect a short in the system—in the compressor, capacitor, or the fan motor. Hire an electrician to track down and solve this problem.

2Make sure the thermostat is set to COOL and its temperature setting is at least 3 degrees below the ambient room temperature.

3Make sure the power is on. Check the switch in the furnace or air handler, and the outdoor condenser. Also make sure no one has shut off the compressor’s 240-volt disconnect, typically in a metal box mounted near the compressor.

4Remove the thermostat’s cover after turning off the power to the air conditioner. Remove the thermostat’s body from the base (usually by pulling straight out) and replace the batteries (if it has batteries). Make sure all wires securely attach to their terminals and that the cover won’t pinch them. Replace the cover and wait 3 or 4 minutes, and then try the system again.

5If that doesn’t do the job, open the thermostat and unscrew the wire from the Y terminal. Turn the power back on. Holding the wire by its insulation only, touch the bare end to the R terminal and hold it there for about two minutes. If the compressor kicks on, the thermostat is faulty; replace it as discussed in the article How to Install an Electronic Thermostat. If the compressor doesn’t go on when you hold the Y wire to the R terminal, turn the power back off and either call an air-conditioning technician or check the capacitor.

6Finally, check the compressor’s capacitor and wires. The capacitor in the compressor starts both the condenser and the fan. If the capacitor has failed, the A/C unit will not run. It’s very easy to test whether it works and it is cheap and easy to fix if it doesn’t.

How to Test the AC Compressor’s Capacitor

Before opening the electrical cover on the A/C unit, be sure to shut off all power to the unit and verify that it is off. Next, remove the cover and, using a digital multi meter set to “Capacitance, ” put one lead on the “Common” terminal and the other lead on one of the other two terminals. The meter should show a number—not “OL” which indicates a short. A/C capacitors can be like two capacitors in one, with both sharing the common leg.

Here is a video that shows more precisely how to do this. Tip: Take a quick digital photo of the wires before disconnecting them so you know where to replace them.

How to Test an Air Conditioning Condensing Unit Capacitor and Wires from oliverfails on Vimeo.

Still not working? Please read “Air Conditioner Not Blowing Air, ” below.

AC Not Cooling Well

If you can hear your central air conditioner running, but it doesn’t cool well, make sure nothing is blocking or limiting air flow anywhere in the system—the air filters, registers, and the compressor. For more about filters, see How to Replace Furnace & AC Filters.

A kinked refrigerant line, or a blower fan that isn’t running right can cause this, too. Next, check the air handler:

How to Check the Indoor Air Handler

1Turn off the power to the air conditioning air handler or furnace. If the air handler is a gas furnace, turn off the gas at the gas valve that serves the furnace.

2Remove the door on the front of the air-handler cabinet so you can access the filter. Pull out the filter and clean or replace it as necessary.

3Look for ice. If you see ice in the area around the coils, close the unit back up, turn the power back on, and turn on the fan. The ice should melt within an hour or two.

Ice In the AC Air Handler

Only two things cause an AC air handler to freeze up: 1) reduced air flow because of dirty filters, coils, or poorly working fans, and 2) low refrigerant level, which a pro must check and, if necessary, recharge. More often than not, the problem comes from reduced air flow.

Clear the Condensate Drain

Air conditioners can create a lot of water because they remove moisture from the air. To get rid of this, they have a [usually plastic] drain pipe that comes out of the side of the air handler. Over time, algae can block this pipe and, when it does, the AC won’t work. In fact, some condensate drains have a float switch that won’t let the AC run if water backs-up. Water can also puddle around the unit or flood the area. To deal with condensate problems, please see Air Conditioner Leaks Water, below.

How to Check the Outdoor Compressor

1Turn off the power. Before cleaning the compressor, shut off all power to the unit and verify that it is off.