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Why Is My Heat Pump Freezing Up in the Summer? 5 Potential Reasons

Two heat pumps outside the house

During the hottest summer months—when you need air conditioning the most—is a terrible time for your heat pump to stop working. A frozen heat pump seems like it wouldn’t be a thing when everything else outside is sweltering, but it’s a more common problem than you’d imagine.

There are many reasons that your heat pump is freezing up, many of which require an HVAC technician to diagnose and fix. However, below we will cover a few of the most common reasons that most homeowners with an average amount of DIY experience can solve.

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The 5 Potential Reasons for a Frozen Heat Pump

1. Dirty Evaporator Coil

The evaporator coil is responsible for absorbing the hot air and using the refrigerant to cool the air. Over time the coil gets dirty, and that causes it not to run as efficiently. Once this happens, the potential for icing up increases.

If you are an experienced DIYer, you can likely tackle this problem. However, if you’re not familiar with working on a heat pump, there is a lot of potential for damage if you don’t clean the coil properly.

There are special kits available with the proper tools for cleaning the coil and preventing the fins from getting bent or damaged.

2. Low Refrigerant

As the refrigerant gets low, the pressure also drops. When this happens, the coil gets colder, and even if it’s clean, it still runs the risk of freezing. Low refrigerant is one of the most common reasons a heat pump will freeze up—even in the hottest weather.

Again, it’s possible to fix this one by yourself. However, if you call an HVAC technician, they will be able to test the system to ensure that there are no leaks in your refrigerant lines.

HVAC Tech Working On A Gas Furnace

3. Airflow Issues

Your vehicle doesn’t run efficiently with a dirty air filter, and neither will your heat pump. If there is not adequate airflow, this can cause the coil to become colder than usual and ice up. As a rule, the air filter should be cleaned or changed every 3 months.

The air filter is pretty accessible in most systems, so you should have no trouble pulling it out to ensure it’s clean.

4. Faulty Thermostat

If the thermostat is not operating correctly, it can cause the system to freeze up because it sends a signal telling the evaporator to get too cold. If your thermostat is faulty, you will likely need to call in an HVAC technician.

On the other hand, another thermostat-related problem is simply setting it too low. Like the above example, if you set the temperature too low, the coil gets too cold, and the condensation freezes—even if it’s scorching outside.

Image Credit: bestv, Shutterstock

5. Fan Belt

A broken or worn-out fan belt can cause all sorts of problems, a freezing coil being one of them. It’s easy enough to inspect the belt for damage, but you will likely need to hire a professional for the fix.

Remember to disconnect the power to the system before checking the belt to prevent it from starting up accidentally and catching your fingers!

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Realized the Heat Pump Isn’t Working, Now What?

If you realize that there is no cold air blowing, the first thing you’ll want to do is look at your thermostat. It’s a common accident to switch the controls to fan mode instead of cool. The other possibility is dead batteries in the thermostat.

If you’ve checked both of these, it’s time to check out the condenser outside. If it’s frozen, you’ll be able to tell right away. There will usually be a lot of frost and ice visible. If there is ice present, most systems will have a defrost cycle—run that.

Once it’s back to normal, turn it onto the regular setting and see if it blows cool air again. If it’s still not working properly, you’ll need to move on to check the other common causes of frozen heat pumps.

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FAQ: Heat Pump

What temperature does a heat pump freeze up at?

If you set your thermostat below 70°F (21°C), you run the risk of the system freezing up. This won’t immediately ruin it but can damage the coil if you continue to run it while frozen.

man fixing the heat pump
Image Credit: Dziurek, Shutterstock

Can you pour hot water on a frozen heat pump?

Absolutely, you can. Hot or warm water will help speed up the defrosting process so you can tell if there are other problems. Melting the ice and frost is the preferred method instead of chipping or scraping the ice off with sharp or hard objects, which can damage the coil.

How do I stop my heat pump from freezing?

A frozen heat pump is one of those things that will happen now and again. A major way that you can avoid it is through proper ongoing maintenance. For example, ensure the vents are always open, change the air filter regularly, and keep the condenser coils clean.

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In most cases, a frozen heat pump is nothing to panic about. There will likely be no lasting damage. Most lasting damage will come from the improper handling of a fix. So, if there is any doubt that you can manage the fix by yourself, it’s a good idea to give your local HVAC company a call and schedule a maintenance appointment.

Even if the heat pump freezes and you’re able to get it thawed out with a defrost cycle, it’s a good idea to call the professionals to service your HVAC systems because that freezing may be the start of more problems down the road.

Featured Image Credit: Nimur, Shutterstock


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