Heat Pump Covered in Ice 101

Ice is a rare thing to see in the Valley of the Sun—at any time of the year. So if you notice ice forming on your heat pump, you probably feel more than a little puzzled.

If it’s winter and you see a light frost on your heat pump, that’s perfectly normal (we’ll explain why later). Your heat pump should periodically go into a brief “defrost mode” to get rid of the frost. After 30 minutes or so, the frost should clear, so there’s no need to call a pro.

However, if the outdoor unit becomes completely iced over, or you see ice on your heat pump in summer (yes, it’s possible), then you have a problem. In these scenarios, you’ll need a professional to repair the system.

In this blog, we’ll explain:

If you’ve read about heat pumps before, you may already know that they use a substance called refrigerant to absorb heat from the outside air. In heating mode, the refrigerant transfers this heat inside, which is how your home stays warm.

During winter, the refrigerant in your heat pump can be anywhere from 10° to 20° F cooler than the outside air. When outdoor air comes into contact with the cold surface of the heat pump, water vapor inside the air condenses and forms frost. You’ll most likely see frost on your heat pump when the outdoor air temperature is below 40° F, and the relative humidity is about 70% or higher.

Your heat pump has a built-in defrost cycle to prevent frost from turning into thicker ice. During the defrost cycle, the heat pump temporarily works in reverse. Instead of sending warm refrigerant into your home, your heat pump sends warm refrigerant to the outdoor unit to melt the frost/ice. While your heat pump is in defrost mode, your backup heat source will kick on until your heat pump goes back to normal.

A little bit of frost is not a cause for concern. But if you see a significant amount of ice forming on your heat pump, you may have one of the more serious problems below.

We’ll share some of the common reasons why ice forms on your heat pump. A professional will need to diagnose and repair these issues.

Like we mentioned above, a heat pump reverses the flow of refrigerant during a defrost cycle to melt away the ice. The part that facilitates this process is called the reversing valve.

That said, if the reversing valve sticks and can’t reverse the refrigerant flow, it can’t melt the ice. In this case, a professional will need to repair or replace the faulty reversing valve.

Frost or ice can quickly cover the outdoor unit if there’s an issue with the defrost controls.

Common defrost control issues include:

• A bad defrost timer
• A faulty defrost thermostat or sensor, or
• A broken defrost relay

A professional will need to check these parts to make sure they are working correctly so that the defrost cycle turns on when it should.

Do you see ice forming on or near the outdoor unit of your heat pump? If so, you may have a refrigerant leak.

We’ll explain.

Your heat pump uses refrigerant in both heating and cooling modes. Refrigerant circulates every season between your heat pump’s units via copper lines in a closed loop.

If one of the copper lines develops a leak, then pressure changes in the line can cause the refrigerant to get very cold. As a result, ice can form on the copper lines—even in the middle of summer. In most cases, you’ll see ice on copper lines that connect to the outdoor unit, but in some scenarios, you may see ice form on the outdoor unit itself.

No matter where you see the ice, you should contact a professional to find the source of the leak and repair it. Otherwise, you’ll quickly notice cooling/heating issues.