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Central Air Conditioner Troubleshooting & Repairs

clean air conditioner

A central AC compressor, located outdoors, should be cleaned before every cooling season.

Save energy and money while making your home more comfortable with these DIY air conditioner repair techniques.

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By keeping your AC unit working well, you can save energy and, as a result, money. If a central air conditioner is in ill repair, it probably won’t work when you need it most.

In addition, if your central AC works but doesn’t cool well, you’re bound to use far more energy than necessary to keep your house cool.

Several different kinds of problems can occur with a central air-conditioning system.

For example, a central AC unit can:

• Not work at all
• Run but do a poor job of cooling
• Allow dramatic changes in room temperature
• Drip or leak water
• Make strange noises

Although some central air conditioner repairs must be handled by a qualified air-conditioning repair person, in this article we’ll look at how you can handle simple repairs and maintenance yourself.

In addition, these two articles may be very helpful for the general care and maintenance of your air conditioner: Preparing Your Air Conditioner for Summer and How to Replace Furnace & AC Filters. The latter is a job that should be handled at least twice a year, before the heating and cooling seasons.

Central Air Conditioner Doesn’t Work At All

Be sure the thermostat is set to "Cool"  if your AC won't go on.

Be sure the thermostat is set to “Cool” if your AC won’t go on.

If your central air conditioner doesn’t go on automatically when the thermostat signals the need for cooling, it’s quite likely that the thermostat isn’t working properly or the unit is receiving electrical power. Before you do anything else, be sure the thermostat is set to COOL and its temperature setting is well below the ambient temperature.
Then do the following:

1Check the main electrical panel and any secondary circuit panels for a tripped breaker or blown fuse. If you find the problem there, reset the breaker or replace the fuse. A central air conditioner should be on a dedicated 240-volt circuit.

2Make sure the furnace power switch is turned on and that the outdoor condenser’s power switch, which is mounted on the outdoor unit, hasn’t been shut off. Also be sure the 240-volt disconnect next to the compressor, which is in a metal box usually mounted on the house wall, hasn’t been shut off.

With this type of electronic thermostat, you pull off the body to access the baseplate and wires.

3Turn off the power to the air conditioner and check the thermostat. Remove the thermostat’s cover 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 or call an air-conditioning technician. If the compressor doesn’t go on when you hold the two wires together, turn the power back off and call an AC technician.

Air Conditioner Doesn’t Cool Well

If you can hear your central air conditioner running, but it doesn’t cool well, the problem can be caused by a couple of issues:

• It needs to be cleaned so that it receives proper air flow, or

• The coolant needs to be recharged by an air conditioning professional.

Cleaning the condenser unit is something you can do yourself with a little guidance. For complete instructions, please see Air Conditioner Doesn’t Cool Well.

If your room has dramatic swings in temperature before the system kicks on, see Room Temperature Too Hot, Then Too Cold.

Air Conditioner Doesn’t Blow Air

If your air handler’s motor runs but the blower doesn’t move air, the belt that connects the two probably has broken. Replacing it is an easy fix if you have a few tools and do-it-yourself skills.
Here’s how to replace the air conditioner’s blower belt:

 

1Turn off all power to the unit and, 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 to give you access to the blower (it might be on a slide-out drawer.) Check the number stamped on the belt and get an exact replacement from a home center or heating supply outlet.

First, fit the belt onto the motor pulley.

3You can usually slip the belt on the motor’s (smaller) pulley first and then start it on the blower pulley, as shown at right. Rotate the blower pulley by hand, holding the belt in place but keeping your fingers from getting caught between the belt and the pulley.

The belt should slip right into place. If it seems to be too tight or difficult to set in place, it may be necessary to adjust the motor mount to provide more slack. Then you can re-tighten the tension once the belt is in place. Check the manufacturer’s specifications for proper tension—in most cases, the belt should deflect about an inch when you press down on it.

4Lubrication. Finally, some fan motors and fans need oiling; some have sealed bearings. If recommended by your maintenance manual, oil the bearings according to the manufacturer’s directions.

Air Conditioner Leaks Water

Air conditioners and high-efficiency combustion furnaces create significant condensation, which exits through a rubber or plastic drain tube and is delivered either to a floor drain or to a small electric “condensate pump” that pumps it outdoors or to a drain. If your air conditioner leaks water or water is pooling at the base of the appliance, condensation may be leaking from one of the tubes that carry it, something may be blocking the water’s flow, or the condensate pump may not be working—if it stops working, it will overflow.

1 Make sure the condensate pump is connected to a working electrical outlet. Then look to see if one of the tubes is leaking. If it is, replace it with tubing purchased at an HVAC supply shop or a well-stocked home improvement center.

 

2 Make sure the electric condensate pump is plugged into a working receptacle, and test the pump by pouring water into its collector. The pump, which is turned on by a ball float inside that rises with the water level, should start. If it doesn’t, it is stuck or broken. If it’s stuck, you should be able to disconnect it from the power and from the inbound tube, disassemble the top, and clean it out thoroughly. If it’s quite old or broken, you’re probably better off replacing it so you don’t have to do this again in the near future.

3 If the pump runs but doesn’t empty the pan, the ball-like check valve just before the discharge tube is probably stuck. Unscrew the check valve, loosen the ball inside, and look for an obstruction. If it appears that a condensation drain tube is clogged with algae, remove it if possible (you may have to cut it and replace it later with a coupling). Blow it out or run a wire through it to clear it—or, better still, replace the entire tube. To kill the algae, pour a dilute solution of bleach (1 part bleach to 16 parts water) into the pump’s trough and pump it out through the tube.

4 Ice may be blocking the tube. If this is the case, clean or change your AC filters. If the filters appear to be fine, the air conditioner’s refrigerant supply is probably low. Call an air-conditioning technician to have the unit recharged.

For more about filters, see How to Replace Furnace & AC Filters.

Air Conditioner Makes Noise

Though most air handlers have direct-drive motors, some older units may be belt-driven. Squealing sounds from a belt-drive air handler generally occur when the belt that connects the motor to the blower slips.

In most cases, the belt is improperly aligned or worn and needs replacement. Follow the instructions above under “Air Conditioner Doesn’t Blow Air” and refer to your owner’s manual.
If a direct-drive blower is squealing or making a grinding noise, shut off the unit and call an HVAC repair technician—the motor’s bearings are probably shot.

Many heating/cooling ducts are metal so they conduct noise quite readily from the air-handling unit to your rooms. To break the conduction of sound, you can have a heating contractor insert flexible insulation ductwork between the heating/cooling system and the metal ductwork.

If you hear a pinging or popping sound coming from metal ductwork, this may be caused by thermal expansion or by air blowing past a loose flap of metal. Track along the duct runs, listening for the sound. If you find it, make a small dent in the sheet metal to provide a more rigid surface that’s less likely to move as it heats and cools.

If the furnace makes rattling noises when it runs, be sure the cover panels are screwed on tight. If they aren’t, tighten them.

HVAC professional checks the refrigerant levels in an air conditioning system.© Ernest R. Prim / Shutterstock.com

HVAC professional checks the refrigerant levels in an air conditioning system.

Getting the Work Done

If you would rather hire an air-conditioning pro to inspect and maintain your AC equipment, this FREE service will help you find a qualified local AC professional.

Call for free estimates from local pros now:
1-866-342-3263


Air Conditioners - Central

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