Central A/C Troubleshooting Tips

Keep Your HVAC System Running Efficiently this Summer

© 2016 by Kelly R. Smith; all rights reserved; content may not be copied, rewritten, or republished without written permission.

An air conditioner condensor array; photo courtesy Ildar Sagdejev

This article was updated on 12/26/20.

Homeowners will be flipping the “on” switch on their their thermostats as the weather goes from cool to warm. In most cases things go just as anticipated. But occasionally, things go a wee bit crossways.

In many cases a bit of A/C troubleshooting solves the problem but other times the problem warrants a visit from an HVAC service company. Read on for common problems and possible fixes.

• The unit won’t turn on. The first thing to check is the circuit breakers at both the electrical breaker box and at the outside unit. Turn it back on if if it’s tripped. The next thing to check is the thermostat.
  
  Put in fresh batteries. It’s possible that it needs to be calibrated. Try that with these thermostat calibration instructions. If a replacement is in order, an Energy Star rated thermostat is a good idea. If the unit has a condensate pump, be sure it’s not full.



• The larger copper line on the outdoor unit isn’t cold. If the fan is running, your refrigerant is probably lacking and needs a charge. Call a service person to check for leaks and add refrigerant; adding refrigerant is something the homeowner can't do without a license but anybody can test.



• There is some cooling but just not enough. Check the temperature differential at two spots, where the air enters and where it exits the air handler. If it’s not between fifteen and twenty degrees, this is another indication of a refrigerant issue.
  
  If it’s much higher, try cleaning the blower wheel and evaporator coil. Also change the filter.



• The A/C isn’t blowing cold air at all. This could be because of a faulty compressor or an inadequate amount of refrigerant in the system. These are problems that a professional needs to address.





• The outside unit is making a loud buzzing. Remove the panel from the outside unit and see if the noise is coming from the contactor (usually a square device with many wires coming out the top and bottom). Before replacing it, as with any electrical repair, carefully label all wires. You might be saying, "I can remember a few wires!" Do it just to be safe; been there, done that.



• A whistling sound may indicate a leak in your ductwork. This can usually be repaired by the intrepid homeowner. Caveat: if you are making a repair with duct tape, use professional-grade metallic backed tape NOT that common grey plastic type (Duck Tape); it won’t hold up in the attic heat and you'll just have to fix it again. Who wants to crawl around in the attic insulation?



• The central air conditioning unit doesn’t seem to be cooling your home adequately. Start by lowering the thermostat five degrees. If that does not fix the problem, you may have a dirty evaporator. Clean it yourself or call a pro.
  
  Carefully clean the evaporator and let it run for a few hours. If the problem remains, it could mean you have an improperly sized air conditioner.

In many cases an HVAC problem can be fixed by the homeowner with these central A/C troubleshooting tips. This, of course, results in saving money, something we all want to do nowadays. The building code mandates that many tasks must be handled by a licensed professional so you'll have to bite the bullet on those. For more information on A/C troubleshooting, check out the article links below. Finally, if a brand new unit is the best way to go, select a high efficiency unit; they are getting better every day.

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