What to Do When Your AC Compressor Isn’t Working

If your air conditioner is not working, the problem can often be pinpointed to the HVAC compressor. This is not necessarily a death sentence for your HVAC unit. Many small, inexpensive and easily replaceable parts are prone to breaking down. Other times, your HVAC may simply need a thorough cleaning.

The problem is often simple enough to be repaired by an average homeowner. Walking through these simple steps will help you determine what to do when your AC compressor won’t turn on and decide whether or not you need to bring in the assistance of a certified HVAC technician.

What Is an AC Compressor?

Your compressor is a critical part of your HVAC system. In residential units, it is typically located as part of the outdoor condenser. The role of the compressor, true to its name, is to compress the refrigerant fluid as it carries heat out of your house. This heats up your already warmed refrigerant fluid even further, converting it from its gaseous form into a liquid.

Though purposefully adding further heat may seem counterintuitive, it is important that the refrigerant be at a higher temperature than the outdoor environment. Especially if you live in areas where summer days can reach up to 120 degrees Fahrenheit. This taps into a basic rule of physics: Heat will always transfer from warm to cool areas. To ensure that the heat your refrigerant fluid is carrying outside is transferred efficiently out of your home, it is crucial that your compressor be well maintained and in working order.

Troubleshooting an AC Compressor That Won’t Turn On

The good news is that it may not be necessary to replace the entire AC compressor. Your compressor is made up of multiple parts that can be replaced individually. If it is one of these parts that is failing, simply replacing the smaller component can reward you with significant savings. Maintaining the smaller pieces can help you get started with HVAC troubleshooting.

Check Electrical Wiring

If your compressor will not start, your first step is to check if your unit is receiving power. Examine all the wiring in your HVAC unit, especially the wiring which connects it to an outlet. If you have a blown fuse or a tripped breaker, this may be the end of your search. An electrician can help you solve the issue.

Perform Easy Cleaning Next

After checking power, begin with the quickest and cheapest maintenance and cleaning tasks, just to rule them out. Before you do anything, make sure you fully shut down your unit. You can do this by pulling the disconnect block out of the electrical box next to the condensing unit. If you have a voltage sniffer, check inside the box to make sure that the power is off.

Buildup of dirt and debris in the evaporators, filters, or condensers can cause your entire unit to shut down. A clogged filter or register can reduce the airflow so much that your evaporator coil will ice up and stop functioning altogether. Regardless of whether or not this is the source of your current AC compressor shutdown, keeping this area clean should be a part of your regular maintenance routine.

A clogged condenser coil can overheat the compressor. In the best-case scenario, the compressor will simply shut down before it is damaged. In the worst-case scenario, continuous overheating can damage the compressor so much that it may need to be replaced.

Clean your condenser coils, replace or wash your filters, and make sure the supply vents are clear of blockages. If your compressor still does not turn on, it may be time to bring in an HVAC technician. A technician will test out the following parts to determine what to do when your AC compressor won’t turn on:

• Capacitor
• Start relay
• Valves
• Terminal connections

If you have a certain amount of electrical know-how, you may want to consider replacing your own capacitors and starter relays before you bring in outside help. If a capacitor or starter relay replacement still does not fix your problem, it is definitely time to bring in a professional HVAC technician. More complex repairs may involve dangerous chemical leaks and other safety hazards that are best handled by licensed professionals.

Examine Your Capacitor and Starter Relays

Ask any technician, and they will tell you that about 85% of HVAC repairs involve electrical systems. Your capacitor and starter relays are critical in providing power to your compressor. These are the items which should be examined first, as they are the most likely to fail. They are also the cheapest and the easiest pieces to replace. If you have basic electrical knowledge, you may consider replacing these parts yourself. If your unit is more than five years old, it may be time for a whole replacement to head off any future problems.

Your HVAC capacitor is a short-term power supply that starts and runs the compressor, as well as the blower motor and the outside fan. Your starter relay transfers power from your capacitors to your compressor. If your HVAC will not turn on, but you hear a humming sound from your outdoor unit, it is likely that this is the compressor attempting to access a non-functioning capacitor. This can overheat your compressor and cause unit-wide damage, so turn your unit off immediately.

If a malfunctioning capacitor is left unattended, the situation can escalate from a simple capacitor replacement to replacing the entire compressor motor. Unlike a capacitor or starter relay replacement, a full compressor replacement should only be performed by a trained HVAC technician, which makes this repair substantially more expensive as well as more time consuming.

Last Resort: A Dead AC Compressor

If the replacements above don’t bring your HVAC compressor back to life, you have two options. You may want a technician to replace your compressor, or you may decide to replace the entire air conditioning system altogether. If the cost of a replacement is less than half of the cost of a new unit, this is likely your best option. But once the replacement price exceeds 50%, it may be time to purchase a newer unit.

You don’t want to be stuck in the heat of the summer with a malfunctioning AC compressor. As soon as you notice a problem with your HVAC unit, call in a professional HVAC technician to take a look and make any repairs and updates that they deem necessary. Cleaning and replacing smaller parts as needed will prevent you from having to replace your entire HVAC unit prematurely.