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How to Fix Air Conditioner

Always be sure to shut off the power to the AC unit at your breaker panel before beginning any repairs. Read the solutions below for do-it-yourself troubleshooting and repairs.

Air Conditioner Repair Walk-Through


  • Adjustable Wrench
  • Driver/Drill, Cordless
  • Garden Hose
  • Insulated Screwdriver(s)
  • Multimeter
  • Needle-Nose Pliers
  • Nut Driver
  • Socket/Ratchet Set
  • Voltage Tester

Extra items you may need

  • ½ Inch Tubing
  • Blower Belt
  • Capacitor
  • Condenser Fan Motor
  • Contactor
  • Compressed Air
  • Fuses
  • Zip Ties

Furnace Fan Working

Sometimes the problem is not with your AC unit at all. Sometimes the problem can be with your furnace. Start by turning down your thermostat and listening for the fan to kick on. If you do not hear the fan running, try resetting your furnace’s circuit breaker. If the fan doesn’t kick on after that, you’ll need to call a professional as none of the tips on this page are going to solve the problem.

Clean Condenser Coils

As we mentioned in the opening paragraph, turn off the power to your AC unit before beginning this phase of work to avoid a nasty shock.

  1. Turn off the breaker to your AC Unit.
  2. Turn off power right at the air handler or furnace.
  3. Remove the disconnect block, by pulling it straight out, of the electrical box which is next to the condensing unit.
  4. Make sure all grass and weeds around the unit are trimmed back and not blocking good air flow.
  5. Take a garden hose over to the Air Conditioner Unit.
  6. Point the hose nozzle upward towards the top of the condenser coils and spray water under the lid to get all the dirt and built up garbage dislodged.
  7. Continue to work your way around all the coils.
  8. Finish up by making the water spray gently into the coils themselves to flush out any left-over debris.

If your condenser coils get clogged up, your compressor can overheat causing it to shut down from time to time. So even if you think your coils are clean, give them another go over before your give up on this solution.

Test Fuses

The disconnect block you removed while checking on the condenser coils contains two fuses. When blown this indicates a large problem in the condenser unit which is causing your air conditioner to fail. Before going forward with any other repairs, be sure your fuses in the disconnect block are not blown.

  1. Obtain a multimeter.
  2. Set it to the lowest Ohms setting.
  3. Put a red lead on one end of the fuse and a black lead on the opposite end.
  4. If there is a reading other than zero, a negative number, or infinity symbol - the fuse is still good.
  5. If the fuse is blown, continue with our walk-through

Replacing the fuse alone will not fix your problem. Continue to follow our instructions below, then replace your fuse and start your AC Unit again. If you continue to have issues after following the instructions below, you will need to contact professional help.

Check for chewed wires or rodent nests

Starting at the electrical conduit on your home, follow it out to your AC Unit. This is your access panel. Again, be certain your power to the unit is off and then remove the panel. Check for any animal nests or chewed wires as this can be a very common problem. If you do find a nest, clean it out. If you find chewed or broken wires (and you feel comfortable working with electrical wiring) then discharge the capacitor and proceed with the repairs. If you’re not confident repairing the electrical damage, contact a professional.

To discharge your capacitor: remove it from its retaining bracket and touch an insulated screwdriver to the H & C terminals. H stands for HERM and C stands for Common. Do the same between the F (Fan) and C terminals as well. If you have a single-mode capacitor, just make a short between the two terminals.

Replace the Capacitor(s)

Every AC Unit has at least one Capacitor. This holds the energy to aid the compressor and condenser fan start-ups. They can give out quickly and all at once or they can do so slowly over time and not be noticed. These are an inexpensive thing to replace and so it’s best to replace your capacitor from time to time (about every five years or so) to stay ahead of potential issues.

  1. Be certain your power to the unit is turned off.
  2. Open the Access Panel
  3. Locate the Capacitor (which looks like a large D-Cell or 9-Volt Battery)
  4. Discharge the Capacitor
  5. Remove it from the retaining bracket
  6. Take a photo of the Capacitor with all the wires still attached so you have a reference for reconnecting them to the new Capacitor.
  7. Take each wire, one at a time, from the old capacitor with a pair of needle-nose pliers and attach it to the new capacitor. Make sure each connector is tight by wiggling it slightly. If you find that it’s not tight, remove and bend the round edges to make a tighter fit on the tab.
  8. When you’ve moved all the wires into the new capacitor, secure it into the retaining bracket and secure all the wires with zip ties.

Replace the Contactor

Located just below your capacitor, and at the top of the list of common air conditioner failures, is the Contactor. This small electronic device costs about $25 and even if yours is working, you might consider replacing it every five years or so. This will help you stay ahead of any potential (perhaps larger & costlier) problems.

  1. Be certain the power to your AC Unit is switched off.
  2. Open your access panel and locate the contactor.
  3. Take a connecter off the old contactor and attach it to your new contactor. Repeat until all connecters are moved over to the new contactor.
  4. Tighten the connecters.
  5. Secure your new contactor into your unit.
  6. Replace the access panel and disconnect block
  7. Turn the power back on to the AC Unit
  8. Turn on the Air Conditioning. You should be able to hear the compressor running and the fan blade should spin. If it doesn’t then your fan motor may need to be replaced.

Replace the Fan Motor

  1. Turn off the power to the AC Unit.
  2. Remove the condenser cover.
  3. Remove the fan blade and motor.
  4. Put a mark on the blade so you know which side of the fan is up.
  5. Loosen the fan blade screws and lift the blade off the motor shaft.
  6. Replace the old motor with the new one.
  7. Be sure to secure the wires with zip ties or the fan blade will cut them.
  8. Replace the fan blade and secure the cover.
  9. Turn the power back on.
  10. Turn the AC on and see if the fan turns this time.
  11. If it doesn’t – it’s time to call a professional. You’ve done all you can.

SPECIAL NOTE – AC Units can take as much as ten minutes to restart after having been powered down completely. Be patient and don’t lose hope if things don’t instantly turn on. This energy saving feature may leave you feeling as though you’ve failed to repair the unit, but they are quite common. Just wait a bit longer before giving up on the unit.

Specific Air Conditioner Problems

AC won't turn On

  1. Check Your Thermostat. Make sure your thermostat is set to "cool." It may sound silly, but sometimes people fail to read their user manuals and don't know how their thermostat works. Ensuring that all your settings are correct should be your first step.
  2. Blown Fuse or Tripped Breaker. Once you've done that, check to see if you've blown a fuse or tripped your circuit breaker that the AC Unit is on.
  3. Drain Problems. AC Units remove water from the air. This is disposed of through a drain pipe that comes out the side of the air handler. Algae can grow in the pipe and when it does, the AC won't work. Some condensate drains have a float switch that will turn off the AC if the water is backing up too much.
  4. Is the condenser running outside? Is it plugged in and getting power? If so, is it making noise at all? Is the fan turning. When was the last time you cleaned your coils? Could they be frozen? Look at our walk-through above for tips on how to handle these common problems.

Air Conditioner isn't Cooling the House Enough

Keep in mind your average AC Unit can only bring the temperature down 20-25 degrees. If it is 110 degrees outside, you cannot realistically expect your home to be cooled to a chilly 68 degrees.

If your room isn’t getting cold the way it should, first check to make sure your register vents are open.

If those check out, be sure you’re getting proper airflow by replacing the filters in your system. This should be done every 60-90 days, perhaps sooner if you have pets or a lot of people in the home. If they aren’t replaced in a timely manner, ice crystals can build up on your evaporator coil causing your AC Unite to stop cooling your home.

If this should occur, you can de-ice the coil by setting your thermostat from “cool” to “off” position and then your fan from “auto” to “on.” You should allow the fan to run for at least thirty minutes or until you feel a good air flow finally coming up through the vents. Then, turn your air conditioning back on. If you’re problem free for at least twelve hours, you’ve resolved this problem.

Lastly, it may be necessary to Clean the Condenser Coil. Reference our how-to above.

Air Conditioner Not Blowing

Be sure to check that the thermostat is set to a cooler than room temperature. Also, consider ruling out other issues which have been mentioned in this article such as closed vents, dirty filters, and iced over coils.

Once you’ve ruled out the above issues, it might be time to look at replacing a blower belt.

  1. Turn off all power to your AC Unit and Handler (which might be your gas furnace.)
  2. Remove the door so you can see the blower and the belt on the side.
  3. If the belt is broken, check the number stamped on its side so that you can purchase an exact replacement.
  4. The belt should be able to slide easily on. Just start by putting it on the motor pulley (the smaller wheel) and then manually turn the larger wheel to twist the belt up onto it. You can adjust the motor mount to provide more slack and then readjust the tightness once you’re done if you think the belt is too tight or difficult to put on. See your owner’s manual for more information or contact a professional if necessary.

Blower isn’t working at all

Check to see if the furnace or other handler is plugged in. Check to see if the door to the furnace is closed fully (some have switches that prevent the blower from turning on until the door is fully engaged.) Check to see if your thermostat settings are correct. Check to see if a fuse has been blown. Check to see if the belt has been broken on your blower. Once you’ve ruled out these, go through our Repair Walk-Through above or contact a professional to inspect your furnace function.

Water Leaking from the AC

On extremely humid days, your air conditioner might create several gallons of water per day and expel it through a plastic pipe drain or tube. This usually goes outside and is expelled somewhere near the compressor or to a floor drain or small electronic condensate pump. In cases where you have an electronic pump, it's normally connected to a 1/2-inch rubber or vinyl tube that goes outside to drain.

Water at the base of your furnace or air handler indicates that either there is a leak in a pipe which carries the water away, something is blocking the flow of water, or that the pump isn't working correctly.

As we said above, some air handlers have a float switch which will shut off the air conditioner if water is backing up. It's the systems way of saying that it's time to clean the drain pipe.

Electronic Pumps
If you have an electric condensate pump make sure it's working correctly and that the breaker to its plug has not been tripped.

Algae has probably clogged your tube or the pump itself and using a wet-dry-vac to pull out the water can be a good solution. In some cases, it might just be easier to replace the 1/2-tubing altogether. Most home improvement stores will have these in stock.

Testing the Pump
Pour water into its collector. The pump should turn on as the water rises. If the ball is stuck or broken it won't rise. If this is the case just disconnect the pump from the power and clean it out. If the float is broke, you're going to have to replace it.

Killing algae is pretty simple, just use one part bleach to 16 parts water through the pump's trough and pump it out.

Pump runs but doesn't empty
Check the ball-like valve just before the discharge. Unscrew the check valve and loosen the ball inside. Look for any algae or other obstruction. Remove it if possible or just replace it all together.

If you find ice is blocking the tube it's time to change those filters. If you've done that recently it may be time to replace your refrigerant (Freon.) Contact a professional to do this for you.

Air Conditioner is making noises

Squealing or Grinding Noise
Most of the time these sorts of noises are coming from a belt that is falling off or worn out. Squealing or grinding is usually a serious sign so turn off your AC Unit immediately and unless you're very handy with this sort of work, you will probably need to contact a professional. If the belt in question is from your blower, see our instructions under "Air Conditioner Not Blowing" above on how to fix that.

Buzzing Sounds
If you hear the buzzing when you turn on the Thermostat then switch the Thermostat to the "Off" position. Then switch the fan over to "On." The fan should come on and if you're still hearing a buzzing sound then it means you have a bad fan relay or blower fan.

If the AC Unit outside is making the buzzing sound, that means your AC is starting to run but the capacitor isn't good anymore. A bad capacitor can lead to an overheating motor when it tries to turn on. With an overheating motor your thermal overload switch will turn the whole system off.

So, when it's buzzing, poke through the grille of your outdoor AC Unit with a stick or long screwdriver and try to turn the blades clockwise. If you can get it spinning and running for a single cycle, but then it stops, this tells you that the capacitor is shot and needs to be replaced. See our Repair Walk-Through above.

If the Compressor is humming when you set the thermostat to "cool" the problem is possibly the low voltage transformer. For this you're going to need to call a professional.

And lastly, if your outdoor unit is making a grinding noise, it's probably the bearings in your motor. This will cause the motor to overheat and cut out. Of course, if this happens, it's time to replace the motor. See the Repair Walk-Through above.

Air Conditioner isn't turning Off

If your AC isn't turning off when the thermostat says the room has reached it's set temp, the problem is usually related to the electrical system that runs outside the condensing unit.

Check to see that your thermostat is showing some sort of reading. If it's blank or shuts off when you switch the thermostat to "heat" you might have a broken thermostat on your hands. Check the battery, and replace if necessary.

If the thermostat doesn't seem to be malfunctioning, the problem may be with one of your wires. It’s possible they've become disconnected or arced. Remove the yellow low voltage wire from your thermostat while the air conditioner is running.

If the unit turns off, either the thermostat is broken or wired badly. Make sure the wiring is right and if you rule that out, then replace with a new thermostat.

If your air conditioner doesn't turn off then you may have relays welded together. This happens over time due to frequent arcing at the relay. Be sure to turn off the power to the furnace and to your condensing unit before you check anything related to this problem. Once the power is off you can disassemble the relay and pry apart the contacts. This is a temporary fix. You should buy a replacement soon.

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