Why Is Your Heat Pump Freezing Up In Winter?

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Heat pump freeze-up isn’t uncommon in the winter. You’d be lucky not to experience it at least once every few years.

It’s also a very dangerous condition. The frozen coils can burst if immediate action isn’t taken. You can also potentially lose the compressor unit.

Therefore, it’s vital to ensure proper maintenance to prevent freezing in the condenser. Checking the condenser unit regularly for blockages and keeping an eye out for signs of freezing can also help. Here’s everything you need to know about heat pump freeze-ups and what you can do.

A Recap

A thin layer of ice on the condenser outside the house during the cold winter weather is normal and completely safe. Even a bit of frost on the coils is normal. It results from the heating process.

When the AC extracts heat from outdoor air, the refrigerant condenses at the outdoor coil. This condensation can free when temperatures outside are extremely low.

A well-running heat pump will periodically go through a defrost cycle to melt the ice and keep the heat pump working regularly. The best part is that the defrost cycle comes on automatically.

However, sometimes you’ll find that the heat pump cannot defrost effectively or quickly enough to get rid of the layer of ice. This can cause the coils inside to be blocked entirely in ice, rendering the heat pump unable to heat efficiently. This is what is known as heat pump freeze-up.

Signs and Dangers of Heat Pump Icing Up

The first sign that your heat pump has frozen up is a permanent layer of ice on the outside condenser. The defrost cycle is designed to get rid of this ice to keep the heat pump running efficiently.

However, if the layer of ice only seems to swell, there could be a freeze-up inside the unit.

Other common signs include;

  • The inner coils appear frozen in ice too
  • The defrost cycle doesn’t seem to be activating
  • Air isn’t being pulled into the AC fins
  • Poor heat output (it feels colder than usual inside the home)
  • A huge power bill

 5 Reasons Why a Heat Pump Freeze Up

Heat pump freezes can result from a range of issues. It could be a technical malfunction, dirty filters, restricted airflow, etc.

1. Technical malfunctions

Although the heat pump applies fundamental physics to move air into your home and cold air out, it comprises multiple complex components with moving parts. These parts can malfunction because of technical failures. For example, if the reversing valve is stuck, the heat pump can malfunction, potentially freezing.

Damaged or poorly functioning fan motors are another technical malfunction that may eventually cause ice buildup on the condenser outside the house. When the fans are damaged, they cannot draw sufficient air into the heat pump. This can reduce the amount of heat inside the heat pump, resulting in icing.

2. Low refrigerant

Another common cause of condenser icing during winter is low refrigerant. Remember that movement of air into and out of the house is solely facilitated by refrigerant material.

Refrigerant is also responsible for moving heat from the condenser to the indoor air handler. It means that the heating cycle is significantly compromised when there’s a low refrigerant level.

Low refrigerant means that the heat pump can no longer carry enough heat into the house. Since the heat pump relies on the same heat to keep internal components warm and facilitate the defrost cycle, low refrigerant levels can cause freezing inside the AC.

3. A malfunctioned defrost cycle

We’ve already seen the role the defrost cycle plays in keeping the air conditioner warm and ultimately preventing heat pump freeze-up. We’ve also seen that low refrigerant can impact the defrost cycle, potentially causing the heat pump to freeze up. Unfortunately, low refrigerant isn’t the only thing that can cause the defrost cycle to fail.

Other reasons the defrost cycle may malfunction include a faulty thermostat, wrong thermostat settings, and extremely cold winter conditions. The good news is that it’s easy to tell when the defrost cycle isn’t working. Signs of low refrigerant, for example, are less obvious.

4. Restricted airflow

Restricted airflow means that the air moving inside your heat pump isn’t to the desired level. When this happens, the heat pump cannot extract enough heat to keep the air conditioner warm. It can also result in defrost cycle failure.

The most common cause of restricted airflow is blocked filters. Blocked filters effectively prevent the smooth flow of air through the heat pump. The filter usually becomes blocked if there’s a buildup of dirt due to poor maintenance.

Blockage can also happen if debris enters the heat pump, blocking the air vents. Twigs, a fallen tree branch, and pebbles can all block airflow into the condenser.

5. Excessively cold winter

Your heat pump can also freeze up if it’s overwhelmed by the excessive winter cold. The standard heat pump is designed to withstand conditions down to 40˚F. Others can do better, up to about 35˚F. However, below that, the unit may become overwhelmed.

One of the first signs that your heat pump is overwhelmed is condenser freeze-up. If conditions outside are too cold for the heat pump to bear, attempts to kick the unit into defrost mode may fail. Alternatively, the unit may get into defrost mode but struggle to melt the ice.

6. Auxiliary heat has failed

Finally, when it comes too cold outside, and the heat pump appears overwhelmed, the unit can activate what’s known as auxiliary heat. Auxiliary heat is a supplementary heat source that runs on electricity. It helps keep you warm even when the heat pump can no longer bring heat into the house.

Auxiliary heat is designed to kick in automatically. As soon as temperatures dip below a certain point, the thermostat will instruct the auxiliary heater to kick in.

However, that doesn’t always go so smoothly. Sometimes the thermostat may attempt to trigger auxiliary heating in vain. When this happens, freeze-up is almost a certainty.

How to Stop Heat Pump from Freezing Up

Fortunately, there are steps you as a homeowner can take to prevent or address heat pump freeze. We recommend the following;

Ensure regular maintenance

It all starts with regular maintenance. If you constantly check the heat pump to ensure that it’s in the best working condition, issues such as icing become rarer.

Way before winter arrives, you should bring in an HVAC professional to inspect the unit and ensure that every component is functioning optimally. From the fans to vents, make sure that all the parts are in excellent shape.

Keep a close eye during winter

You must be even more careful during winter, as freeze-ups typically happen during the cold season. Walk around the outdoor condenser at least every 1-2 days to make sure that there’s no airflow blockage. Also, make sure the ice layer doesn’t grow too thick. If it keeps growing and never recedes after 2-3 days, there’s a problem.

Know When to Call the Pros

As we’ve mentioned repeatedly, heat pump freeze up can be a dangerous thing. It often starts as a harmless ice layer. However, the problem can worsen in a matter of days, causing untold damage inside and outside the house. Calling an HVAC technician on time can salvage the situation.

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