Heat Pump Capacitor: What You Need to Know

As a homeowner, the more you know, the better you can care for your home and its systems. Your heat pump system is no exception. Keep reading to learn more about heat pump capacitors and the problems they can cause if they go bad.

An air conditioner or heat pump capacitor falls under the umbrella term of an HVAC capacitor. Housed in the outdoor condenser unit, the capacitor is a silver cylindrical canister that looks like a cross between a battery and a tall boy can.  It’s a relatively small component that plays an outsized role in starting your heat pump and keeping it running. 

The capacitor is connected to electrical wiring so that it can store electrical current. It gives the compressor motor and fan motor a little jolt of electricity to help them start when the thermostat calls for heating or cooling. Once the heat pump starts, the capacitor supplies a steady current of power to keep the unit running until the heating or cooling cycle is finished.

There are 3 kinds of HVAC capacitors:

• Start capacitor
• Run capacitor
• Dual run capacitor (dual capacitor)

Older air conditioning systems and heat pumps have two capacitors - a start capacitor and a run capacitor. One sends the initial jolt of electricity to start the unit while the other keeps the unit running.

Newer AC units and heat pumps use a dual run capacitor or dual capacitor. This capacitor handles both the start and run functions. It essentially contains two capacitors in one canister. 

HVAC capacitors are measured in voltage and microfarads (MFD). The voltage rating measures how much electrical current is moving through the capacitor. The more voltage in your capacitor, the faster the electrical current moves throughout it. Microfarads describe how much electrical current the capacitor can store. Most capacitors range from 5-80 MFD. 

The biggest reason for a capacitor to fail is overheating. An HVAC capacitor can fail due to wear and tear over the years, or it can give up during an extended run time such as during a heat wave. It may also fail because an aging compressor is drawing more energy each time it starts.

There are a lot of signs of a failing or failed capacitor, which we list below. Other issues can also cause these symptoms, so your best bet is to call an HVAC company to get to the bottom of your heat pump problems.

If the heat pump is not turning on, it could be a bad capacitor to blame. But it could also be several other things. Make sure the heat pump has power - check the circuit breaker to make sure it hasn’t tripped. If it has, reset it. If it trips again, call an HVAC professional.

Make sure the thermostat setting is set to Cool mode or Heat mode, and that the temperature is set above or below the current indoor temperature. If the HP doesn’t kick in after checking the power to the unit and the thermostat, call for HVAC repair.

If the heat pump is not heating, or it’s not cooling, there can be many reasons, one of which includes a bad capacitor. But if the compressor is running and the fan is turning, the problem is something other than your capacitor. Check to make sure your thermostat is on the right setting and the fan setting is set to Auto for a start. If that doesn’t solve the problem, contact an HVAC professional.

If you go and stand next to the outdoor unit, you may hear the capacitor clicking every few seconds if it is bad. This sound is the heat pump capacitor trying to release the energy needed for the compressor and fan motors to start. If the start capacitor has failed, you may also hear the motor making a loud humming noise. If you’re experiencing this issue, call for heat pump repair.

Another sign of a bad capacitor is if the unit is running but the heat pump fan isn’t spinning. Remember we said the capacitor helps power the compressor motor and the fan motor? This issue could be due to several reasons, including the capacitor. 

Your best bet is to call an HVAC professional to troubleshoot. The exception is if you see that debris such as leaves or twigs have gotten into the unit and are impeding fan movement.

If the outdoor unit smells like burning, it could be the result of a failing capacitor, failing compressor, failing fan motor, or a combination of these things. Overheating components can give off a burning rubber smell or a burning electrical smell. Turn the unit off and call for heat pump repair.

This is not a DIY job. AC and heat pump capacitors are high-voltage components and should only be tested, discharged, or replaced by a trained HVAC professional. They will know how to test a capacitor with a multimeter to see if it works properly or needs replacing.

However, they may not need testing to tell that the capacitor needs to be replaced. Visible signs of a failed capacitor include bulging, cracks, and oozing liquid. 

While we’ve heard of capacitors lasting 20 years, most don’t last that long. Heat pump capacitor replacement, along with AC capacitor replacement, is one of the most common HVAC repairs. The average HVAC capacitor replacement cost is $100-$400. The part itself is not that expensive, but the service call fee and labor costs add to the final cost. The repair can typically be done in less than an hour if there are no other issues. 

Heat pump capacitor replacement is not a DIY job. It requires special training and special tools. You could injure yourself or damage your HVAC system if you attempt to repair it yourself. In addition, if your unit is under warranty and you try to fix it yourself, you could void the warranty. 

For reliable home comfort, make regular heat pump maintenance a priority. Maintaining your heat pump system can help your heat pump run more efficiently, keep you comfortable, and keep your energy bills under control. Neglecting HVAC system maintenance can cause problems and cause your heat pump to fail sooner. 

Clogged air filters can cause a lot of problems. Change standard HVAC air filters every 1-3 months. Change or clean the filter on a whole-house air purification system as directed in the owner’s manual. Refer to our air filter maintenance guide for tips.

Protect your system and schedule professional service for each fall and each spring. Be sure to hire an HVAC company with expertise in heat pump systems.

Did you know your Trane dealer can monitor your HVAC system’s health? When you opt into Trane Diagnostics via the Trane Home App, you give your dealer remote monitoring capabilities of your heat pump system. Your Trane smart thermostat sends data in real-time to your dealer, alerting them to any issues such as a failing capacitor,

They can run heat pump troubleshooting tests to narrow down or even pinpoint the problem. In some cases, they may be able to fix the problem remotely. In this situation, they would ask for one-time dealer remote access (DRA). 

If they need to schedule on-site heat pump repair services, the HVAC technician will arrive at your home with the knowledge gained from remote troubleshooting. This results in shorter service calls and ensures the technician has the proper replacement parts.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Kimberly Sexton, Senior Systems Engineer

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