Erin Doman on May 30, 2016 34 Comments HVAC Troubleshooting: How to Fix An HVAC Compressor That Won’t Turn On 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 HVAC 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 HVAC Compressor? Click Here to View All HVAC Compressors on Amazon Your compressor is a critical part of your HVAC system. In residential units, it is typically located as part of the outdoor unit. 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 in to 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. Maintaining the Smaller Pieces The good news is that it may not be necessary to replace the entire HVAC compressor. Your compressor is made up of multiple parts which can be replaced individually. If it is one of these parts that is failing, simply replacing the smaller component can grant you significant savings. Check Electrical Wiring If your compressor will not start, your first step is to check and see 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. It is time to bring in an electrician who will help you decide what to do when your HVAC compressor won’t turn on. Easy Fixes First 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 HVAC compressor shut down, keeping this area clean should be a part of your regular maintenance routine. Click Here to View All Through-the-Wall Air Conditioners 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. Go ahead and 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 HVAC 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 which are best handled by trained professionals. Your Capacitor and Starter Relays Ask any technician, and they will tell you that about 85 percent 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 which 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. Turn your unit off immediately. This can overheat your compressor, causing unit wide damage. If left unattended, this can elevate the situation from a simple capacitor replacement to a need to replace 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. A Dead HVAC Compressor If the replacements do not bring your HVAC compressor back to life, you have two options. You may have a technician 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 most likely your best option. Once the replacement price exceeds 50 percent, it may be time to purchase a newer unit. Troubleshooting Your Malfunctioning HVAC Compressor You don’t want to be stuck in the heat of the summer with a malfunctioning HVAC compressor. As soon as you notice a problem with your HVAC unit, you should call in a professional HVAC technician to take a look and make any repairs and updates that they deem necessary. Replacing smaller parts as they need them will prevent you from having to replace your entire HVAC unit prematurely.