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Air Conditioner Troubleshooting

If your air conditioner is not functioning right, save money and time by checking out these air conditioning troubleshooting tips. With a little guidance, you can repair many air conditioner problems yourself.

Common problems

There are several common issues with air conditioner units. The unit may not work at all, or it may run without cooling. Fluctuating or incorrect temperatures may indicate a thermostat problem. Homeowners also complain of leaky air conditioning units or a system that makes odd noises. It can also be a problem when the air conditioner does not turn off. Read bellow to find troubleshooting tips for these problems and more.

Checking the thermostat

Troubleshooting an air conditioner begins with the thermostat controls. Set the thermostat to the ON position. If your air conditioning unit also has heat capabilities, be sure the thermostat switch is on the COOL setting.

Finally, double check the temperature settings to make sure the thermostat temperature is set at least five degrees lower than the room temperature. This procedure should trigger the unit to kick on and blow cool air. While taking these steps may sound a bit simple, it is easy to overlook the thermostat settings when troubleshooting air conditioners.

Replace old thermostat batteries

Before checking the batteries, make sure to turn off the power to the AC unit. Remove the thermostat cover, then take out the internal unit. Make sure the batteries are connected correctly and adjust them if necessary. If the old batteries are in the right position but the air conditioner will not work, replace them with new batteries.

While the cover is off, check the wiring for breaks. If you have a broken wire, you may be able to repair it with electrical tape. If the wiring appears burnt or frayed, stop. Do not attempt further repairs without talking to a heating and air conditioning expert.  

Not working at all

A non-working air conditioner can indicate a tripped breaker switch or a short in the electrical system. First, check the main breaker box and any secondary circuit breakers for a tripped breaker or a blown fuse. Reset any tripped breakers by flipping the lever OFF and then ON again. If your breaker box has fuses instead of breaker terminals, replace any blown fuses.

If the breaker continues to shut off, there could be a short in the unit’s electrical system. You will need a licensed electrician to diagnose and repair a short in the air conditioner. Without significant electrical experience, attempting these repairs yourself could be dangerous.

Not blowing cold enough

Check to make the air conditioner thermostat is set to cool and that the fan is on. If the settings are right, and the unit still is not blowing cold air, try these troubleshooting steps.

  1. Turn off the unit. Disconnect power at the circuit breaker. Make sure any power cords are also unplugged.
  2. Check the air filter. A dirty filter prevents good airflow. Clean or replace it if necessary.
  3. Look at the coils. If they are covered in ice, you will need to defrost the air conditioning unit. Turn on the power and fan and run the unit without setting it to COOL. This should melt the ice within an hour or two.
  4. Clean the condensate drain. Removing any debris or blockage should get your air conditioner working again.
  5. Inspect the outdoor compressor. Leaves and other debris can sometimes clog the compressor fins. Clean it if necessary.

Making weird noises

Noises may occur in the unit’s air handler or the outside compressor. The solution to the problem depends on the noise and its location.

Air conditioner handler squealing or grinding

Air handlers with belt-driven motors may have a loose or damaged belt. Turn off all power to the unit at the breaker. If the air conditioner is part of a furnace system, turn off the gas as well. Next, remove the door from the front of the air handler cabinet. Check the belt for signs of wear and replace it if necessary.

Fit the new belt to the smaller of the two pulleys you see. Start it on the larger pulley, then rotate the same pulley to help the belt slip into place. Use a screwdriver to loosen and adjust the motor mount if necessary. The belt should have about an inch of give to it when you press down on it. However, double check the tension specifications in your owner’s manual.

Air conditioner handler buzzing

A buzzing noise when you switch the thermostat to ON can indicate a problem with the blower fan or its relay. First, move the thermostat COOL switch to OFF. Next, make sure the fan switch is in the ON position. If you hear buzzing, you will need a technician to replace your blower relay or the entire fan.

Air conditioner compressor buzzing, humming or grinding

If your thermostat is set on COOL and your AC compressor is humming, the low voltage transformer may be faulty. Grinding noises are likely coming from worn-out motor bearings, which means the motor needs to be replaced.

A buzzing outdoor unit may have a problem with the run capacitor. If the capacitor is bad, the motor will overheat and shut off after a few minutes. For safety’s sake, you will need a licensed technician to perform repairs for any of these issues.

Will not turn off

There are two common reasons for an AC unit that will not turn off: dirty condenser coils or a thermostat with a short in it.

Dirty condenser coils

The condenser coils disperse the heat as refrigerant runs through the coils. When the condenser coils are dirty, they are unable to disperse the heat properly. The air conditioner will become less efficient; the more soiled the coils become, the harder the motor works to produce cold air. Check and clean the condenser coils if necessary. Make sure you switch off the power at the circuit breaker before beginning work on the unit.

A short in the thermostat

The thermostat sends voltage to the compressor and fans motor. If the thermostat has a short, it could send constant voltage to the compressor, causing it to run without stopping. Use a multimeter to check the thermostat for continuity. If it does, replace the shorted thermostat with a new one.

Overflowing drip pan

It is typical to find a small amount of water in the air conditioner drip pan; warm air over cold coils condenses into water. The water travels down a pipe and into the drip pan. Normally, the condensate pump automatically switches on when it detects moisture. If the drip pan overflows or becomes unusually full, it could be a sign that the condensation pump is damaged or broken.

Another possibility for drip an overflowing drip pan is a clogged drain line. Algae, calcium, and mineral deposits can build up in your drain line, causing it to clog. A clogged drain can cause water to back up and begin to flow into the drip pan. Use a long, thin wire to clear any clogs. Flushing the drain line with a mild bleach solution will help prevent algae buildup.

Air conditioner problems can be a hassle, especially in hot or humid weather. Fortunately, you can repair many of them yourself. Regular maintenance also helps. Change or clean the air filter monthly while the air conditioner is in use. You should also have a heating and air conditioning technician check your unit annually.

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