How To Troubleshoot an Air Conditioner Failure

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DIY Air Conditioning Fixes 

When your air conditioner isn’t working, you don’t need to get hot under the collar. There are a few things you can do to troubleshoot AC issues and possibly even do the repairs yourself. Even if you can’t do the repair, you can eliminate some possible causes of the problem so a professional technician spends less time on diagnosis and more quickly solves the problem to get your AC back up and running.

In this post, we provide some easy tips on how to troubleshoot an AC failure and give you some no-sweat steps you can take to fix it yourself:

Initial Diagnosis

Eliminate the Furnace

Make sure the problem isn’t the furnace. Set the thermostat to AC mode and lower the temperature. If the furnace fan comes on, that’s good–that means the problem most likely is not the furnace itself. You can read on to see if there’s anything you can do to fix the AC unit.

If the fan doesn’t run, reset the circuit breaker. If the furnace fan still doesn’t come on,  unfortunately you have a serious problem. Call an AC repair company.

Check the Outside Condensing Unit

Are the compressor and fan in the outside condensing unit running? If you hear a sound like a refrigerator running, then it is. If it is and you still don’t have cooling, you may want to stop here and call an experienced AC person.

If the compressor and fan aren’t working, read on and follow the recommended steps.

Tools You Need

The tools you need include:

  • Adjustable wrench
  • Cordless drill
  • Insulated screwdriver
  • Needle nose pliers
  • Nut driver
  • Socket/ratchet set
  • Multimeter
  • Voltage tester

If you don’t have these tools readily available, or possibly don’t feel sufficiently knowledgeable about the use of some of these tools, particularly a multimeter or voltage tester, or you aren’t comfortable working with electrical components, call an experienced AC service.

Parts List

Here are the parts you need:

  • Capacitor
  • Compressed air
  • Condenser fan motor 
  • Contactor 
  • Fuses

The problem may be with only one of these parts; however, if you are going to the trouble of opening up the outside condensing unit, you might as well replace all these parts. The cost is minimal and, particularly if the unit is five years or older, replacing these parts helps ensure future smooth running. The one exception is the condenser fan motor, which is fairly expensive. Don’t replace the condenser fan motor unless you are certain it is not functioning.

The list is also generic. Make sure you obtain parts for the make, model, and serial number of the unit. This is found on the nameplate on the condensing unit. Most parts are available online, at an appliance store, or from the manufacturer.

AC Overview

Before you can fix a central air conditioning system, you need to understand how it works. There are a few major components:

  • Outside condensing unit 
  • Evaporator coil (aka A-coil) situated in the furnace air handler 
  • Furnace or indoor air handler
  • Thermostat

Here’s how these components work together:

Refrigerant in the A-coil absorbs heat from inside your home and transports it to the outdoor condensing unit. The condensing unit fan blows outside air through the condensing coil to remove this heat and circulate cooler air back into the home.

There are no parts in the A-coil. Only a professional AC technician can service the A-coil.  

The condensing unit houses a compressor, which also only a professional AC technician can service.

The three parts you can replace in the outside condensing unit are: 

  • AC contactor. This is a mechanical relay that employs low-voltage power from the thermostat to switch high amperage current to the compressor and condenser fan. 
  • Start/run capacitor(s). The capacitor stores electricity and releases it as needed to provide extra power to the compressor and condenser and minimize voltage fluctuations that can damage them.  
  • Condenser fan motor.

8 DIY Steps to AC Maintenance and Parts Replacement

Follow the steps below to replace parts in the outside AC condensing unit.

  1. Turn off the AC and furnace breakers.
  2. Open the electrical box next to the condensing unit; pull out the disconnect block. (Make sure to switch the breakers off at the main panel)
  3. Use a voltage meter on the wires in the electrical box to ensure power is off.  
  4. Spray the condenser coil with a garden hose to remove any dirt or debris that can impair the efficient functioning of the coil. Be sure not to push the debris into the coil and cause it to clog. Spraying from the inside out is best.
  5. Use a multimeter to check the fuses in the disconnect box. 
    1. Set the multimeter to the lowest OHMS scale. 
    2. Touch the red and black leads to the opposite ends of the fuse. 
    3. A numerical reading = the fuse is good; a 0, – or ∞ shows a blown fuse. Note: A blown fuse indicates a parts failure. Replacing a fuse does not solve the problem; the fuse is likely to blow again. Instead, replace the blown fuse after you replace the parts.
  6. Remove the access panel. Remove any debris, particularly rodent nests, as these creatures tend to chew on wires and electrical connections. 
  7. If you find broken or chewed wires, remove and discharge the capacitor and replace the connections. To discharge a single-mode capacitor, touch an insulated screwdriver between the two terminals. To discharge a dual/start capacitor:
    1. Touch an insulated screwdriver between the H and C terminals.
    2. Touch the insulated screwdriver between the F and C terminals.
  8. Use a needle nose plier to disconnect the capacitor wires and install the new capacitor. (Pro tip: take a photo to ensure you have a reference to reconnect the wires correctly.) 

Test Your Repairs

Fingers crossed, the replaced parts fix your AC system issues. To make sure:

  1. Reinstall disconnect block and access panel.
  2. Turn on the circuit breaker to the HVAC system and furnace switch.
  3. Set the thermostat to a low temperature and wait to see if the compressor and condenser fan run. Note that this can take up to about a half-hour for the unit to totally reset and repower. Don’t get discouraged if nothing happens right away.

If the compressor and condenser fan run, pat yourself on the back and get inside to cool off. If they aren’t running, then the culprit is the fan motor. For this, you need to contact an HVAC professional.

Your AC Partner

If all this seems a bit overwhelming, we here at Ongaro & Sons can quickly help you get your cool back. We’ve been in business over 90 years, providing high-quality service using only the highest quality equipment. Ongaro & Sons is a licensed state contractor and our qualified technicians are fully insured. Our 100% guarantee ensures your complete satisfaction. 

Contact Ongaro & Sons today if you need an AC repair, or if you are considering a new AC system. If it’s an emergency, call us at 707-730-2943. We look forward to serving you so that you can maintain your cool.