Why Heat Pump Compressor Not Turning On?

When the weather gets chilly, you want your house to be warm. And when your heat pump compressor refuses to start, you want to know what the problem is and how you can fix it. 

When your heat pump compressor is not turning on, the issue is with either the thermostat, the power supply, refrigerant levels, or the frozen outdoor unit. Fortunately, you can some of these problems without the help of a repair technician.

If you’re having heat pump compressor problems, I have solutions. Let’s start with a brief explanation of how your HVAC system works and will also cover the reasons your heat pump compressor isn’t turning on.

How Does a Heat Pump Compressor Work?

If you have ever cleaned a keyboard with compressed air, you have probably noticed that the can becomes colder as you spray. When a gas is depressurized, it loses heat, and when a gas is compressed, it becomes hotter. 

Your heat pump compressor works by pumping refrigerant through a system of coils that compress the gas and make it hot, then decompress it and make it cold. In AC mode, a fan blows cool air into your home, while heating mode blows warm air instead.

Your HVAC system cannot function without its compressor. So what are some reasons why your heat pump compressor has stopped working?

Reasons Your Heat Pump Compressor Isn’t Working

When faced with an unresponsive heat pump, the first thing you must do is determine the cause. 

Like surgeons, we should start with the least invasive procedures since what seems to be a catastrophic failure at first glance often turns out to be a trivial issue.

Check Your Thermostat

If your heat pump refuses to turn on at any thermostat setting, you could have a problem with the heat pump, or the problem may lie with your thermostat. 

Here are some things you can do to fix any thermostat-related problems that may be plaguing your HVAC system:

Clean Your Old Thermostat

As mechanical thermostats age, they become less accurate. Dirt and grime accumulate in the machinery, while wear and tear mean things aren’t as precise as they once were.  

Clean your mechanical thermostat by removing the cover, then dusting the inside lightly with a soft brush. Slip a piece of paper between electrical contacts and move it back and forth to knock away any debris that might be blocking a connection.  

Check Your Thermostat Batteries

Electronic thermostats can only control your HVAC if they are getting adequate power from their batteries. If you see a low-power light on your thermostat or app, replace your old batteries with new ones. 

Even if you don’t see an alert, replacing your batteries with new ones will never harm your system. What’s more, they cost significantly less than an HVAC repair visit. 

Keep Your Old Thermostat Cool 

If your space heater is near your thermostat, your heat pump may not come on matter how cold the rest of the house gets. 

Move any heat sources away so your thermostat can get a true room temperature reading. 

Replace Your Old Thermostat

Making your HVAC part of a smart home system is easy with a smart thermostat. I recommend the Emerson Sensi Wi-Fi Smart Thermostat (available on Amazon.com), which comes with DIY installation instructions and is compatible with Alexa.  

70% of users report installing the Sensi took 30 minutes or less to get it set up. Additionally, if your old thermostat refuses to respond, the Sensi lets you control the heat by app or voice.

Check the Heat Pump’s Power Connection

Heat pump issues can often be traced to a blown fuse or tripped circuit breaker, so make sure to check your box and replace the HVAC fuse or reset the breaker. 

Before you reset the breaker box, make sure your heat pump’s power switch is turned on. If the circuit trips a second time, do not turn it back on until you have determined why the heat pump is drawing excess power. 

While this may require the services of an HVAC technician, here are some things you can do on your own first:

Check Your Air Filters

The dirtier your air filters, the harder your HVAC system has to work to get the heated air from the heat pump into your home. That extra work taxes the blower motor and causes it to draw more current until the breaker trips.

Left unchecked, this dirt can get into the heat pump’s inner machinery and cause irreparable damage. If your filters are dirty, change them immediately. 

Most HVAC manufacturers recommend you change filters at least every 90 days. If you have dogs or cats, you may need to change filters more frequently, as the filters can get clogged with pet dander. 

Check the Outside Temperature

If your area experiences a cold snap, your HVAC system may be pushed to working past its capacity. The auxiliary heat comes on when the air gets too frigid for your heat pump to warm it sufficiently. 

The auxiliary heater uses much more electricity than your heat pump and can easily trip the circuit breakers if overtaxed.

Your best immediate response in this situation is to turn the heat down and put on a sweater. Once temperatures are back to normal, talk to an HVAC contractor or electrician about increasing your heating system’s capacity.

Check if Your Outdoor Coil Is Frozen Over

If your outdoor coil is covered with ice, airflow is blocked, and the coil becomes much less effective. 

This means the heat pump has to work harder, often so hard that it shuts down. 

If your outdoor coil is iced over, do not chip the ice off as that is likely to damage the refrigerator coils and fins. Shut the system down until the ice melts off and until you determine what is causing the problem.

Some reasons your outdoor coil might be frozen over include:

Water Leaks and Storms

Icy water spilling from a gutter running off a roof can easily overwhelm an outdoor coil’s defrost capabilities. Fix any water leaks or runoff issues that may be causing a problem.  

Not only can leaky or overflowing gutters lead to water on your outdoor coil, they can also produce large icicles that can do serious damage to your system if they fall. 

Ice storms and heavy snows can also lead to freezing. After a snowstorm, ensure a 2-foot (61 cm) clear radius around your coil for proper air circulation.

Air Circulation Blockage

Wet fallen leaves or a snowdrift can block air circulation and interfere with the HVAC’s heating and cooling functions. 

Clear away anything blocking the outdoor coil’s air circulation. Let the ice melt before restarting the heat pump.

You may also consider building a shelter around your coil to protect it from the elements. A canopy will make your system run more efficiently in both summer and winter, but be sure you have at least 2 feet (60.96 cm) of clearance on all sides and the top.  

Low Refrigerant 

Your HVAC system’s evaporator coil should get chilly enough to lower the air temperature but not cold enough to cause frostbite. You don’t want arctic air pumped into your living room even on the hottest day!

When your system runs low on refrigerant, the pressure in the evaporator coil drops, and so does the evaporator coil’s temperature. 

If your HVAC system is low on refrigerant, you will need to consult a technician. Low refrigerant levels mean that there is a leak in your system, which you’ll need to deal with before adding more gas. 

Malfunctioning Defrost Timer

If your outdoor coil keeps freezing over at or below a certain outdoor temperature, you may have an HVAC system that is undersized for your climate. 

If your outdoor coil is suddenly freezing over at temperatures it previously handled with no issues, its defrost timer may be malfunctioning.

To prevent icing, your outdoor coil has a defrost cycle. During the defrost cycle, your HVAC switches from heating back into air conditioning mode.

The coils which were carrying vapor at around 45 °F (7.2 °C) are now filled with liquid refrigerant at a temperature of approximately 150 °F (65.5 °C). This warms the pipes and melts any built-up frost. 

If your outdoor coil’s defrost cycle doesn’t kick in when the temperature drops, it will soon ice over. However, if your outdoor coil’s defrost cycle is too ambitious, that can cause other problems.

While the outdoor coil defrosts, your indoor coils are once again carrying cold vapor. The indoor HVAC fan shuts down during the defrost cycle to keep that cold air out of your house.

Check if your HVAC coil is stuck in defrost mode if your heat pump refuses to kick on. Your heat pump should defrost no more than once every 30 minutes and for no longer than 10 minutes.

To Sum Up

Your HVAC system is useless if your heat pump fails, but heat pump repairs are expensive, and you’d probably like to avoid the bill if you can.

The troubleshooting tips above will help you avoid HVAC issues in the future and may even solve your immediate problem. 

However, if your heat pump compressor is still not working, you will need to call in professional help. HVAC systems are complicated, and amateurs can wind up doing further damage – which only means a bigger bill.

Good luck with your heat pump, and stay warm!