Heat pumps typically freeze in cold weather, particularly if the area where you live has high humidity. This can occur even if the outdoor temperature is above freezing. Because the outdoor coil on your heat pump is typically 10 to 20 degrees colder than the outdoor air, if it is a 39 degree day the outdoor coil may be as cold as 24 degrees. If on that same day the dew point is as high as 33 degrees then moisture will have no option but to condense on the surface of the coil. Since it freezes at 32 and the coil is at 24, the moisture turns immediately into frost.
It is perfectly normal to have light frost on a heat pump, but if the system is encased in ice or doesn’t defrost itself within 3-4 hours, something could be wrong with the defrost functionality. This is especially a risk during cold or freezing rain, as well as snow. If your heat pump doesn’t seem to be defrosting properly, you will need to call in a professional to thaw and maintenance the heat pump without delay. In many cases however, getting your heat pump running smoothly again after a freeze up is something you can handle easily on your own.
Temporary freeze ups are a perfectly normal occurrence for heat pump systems, which automatically defrost themselves. The real issues only occur if a heat pump freezes up for more than 4 hours and doesn’t seem to be defrosting itself properly. If your heat pump freezes up for more than 4 hours, there could be a problem that may include: faulty sensors, thermostat, or defrost controls, low refrigerant levels, or even a bad frost relay. Poor drainage, malfunctioning of the outdoor motor, or even improper leveling of the equipment could all contribute to a freeze up.
Your heat pump’s defrost system usually has a timer that requires the compressor to run for a given period of time before it will start a defrost cycle. These timers can be anywhere from 30 minutes to 2 hours as set by the manufacturer. Attached to the defrost system is a defrost sensor. This sensor tells the defrost system that the coil is frosted over. Some manufactures program the defrost system to start the timer only after the sensor has recognized the frost. Others will start the timer after the last defrost cycle and will ignore the sensor until the unit has ran for the selected time, at which point if the sensor has recognized the frost, and defrost will initiate. Most defrost controls will limit the defrost cycle to a max of 10 minutes. This is typically more than enough time to remove the frost.
The worst case scenario for a heat pump however, is when there is snow falling. First, the conditions are already perfect for moisture to freeze on contact on the outdoor coil. Second, as the outdoor fan motor pulls air across the outdoor coil, those beautiful white snowflakes that are floating towards the ground get drawn into the coil. In this case, the system may finish a defrost cycle and within just a few minutes have pulled enough snow in the coil to require another defrost cycle.
If there is any form of frozen precipitation falling (snow, freezing rain, sleet), change the mode on your thermostat to E-heat. Also, If the weather forecast is calling for a hard freeze warning and you see frost on your unit for more than 1 hour, then use E-heat. Once the weather conditions have improved, if you still have concerns about the frost on your unit, give a call to a service provider to insure your unit is working properly.
Investing in a regular HVAC maintenance plan is also a good way to prevent against freeze up issues. Your technician can help you anticipate the freezing conditions that lead to freeze ups, and keep your system running smoothly year round.
So despite all the your best efforts and preventative measures, your heat pump still freezes up. What do you do now? Don’t panic, this is a normal issue with heat pump systems and there are solutions. We’ve listed out the best solutions below.
Your heat pump’s defrosting system, especially if it’s a newer system, likely has no issues and is working hard right now to get your system thawed and running again. Sometimes it can just take some time for the defrost system to do its work, which can make it seem like there’s a problem where there isn’t none. The best advice we can give you is to have some patience. If your heat pump doesn’t seem to be running, just give it 3-4 hours to defrost itself. This will almost always solve the issue and your system will kick back in and continue heating without any noticeable temperature drop within your home.
If you’ve given your heat pump at least 4 hours to defrost itself, and it is still not operating normally, your best bet is to give us a call and schedule service from one of our HVAC technicians. Additionally, scheduling regular HVAC service can help you avoid common issues like this that cause your heat pump to freeze up, and keep your system running smoothly year round.
There are a few other solutions that you, as the homeowner, can try if you’re in a pinch and you’re comfortable with troubleshooting complex equipment on your own. Be forewarned however, by following these steps when you don’t know what you’re doing, you could make the problem worse or even damage your heat pump. Only proceed if you’re ok with that risk, you’ve already given your heat pump at least 4 hours to defrost itself, and calling in a professional technician is not an option.
One thing you could try to do to unfreeze your heat pump (if your system is equipped with it), is simply turning on the fan. Blowing air will usually thaw the equipment within 60 minutes. If the outdoor temperature is particularly low, you can set up the fan on an exhaust setting. Running the fan for a while might not solve all problems and freezing issues, but it is a short term solution you can try. Not all systems have a fan setting however. For example, the Bryant heat pumps we install do not have this option, but some other systems do.
Another possible solution is to manually turn on the defrost cycle. The defrost cycle works by reversing the valve to air conditioning mode, which switches the outdoor fan off and turns the outdoor evaporator into a condenser. This helps warm the high-pressure refrigerant and melts the ice when the it circulates through the outdoor coil. The heat pump should run its defrost cycle automatically, but if it isn’t thawing itself then it may need to be manually switched on. Again, not all systems may have an option to manually run the defrost cycle, at least not easily. You will have to do some research on your particular system in order to confirm.
The final alternative solution you can try on your own, is moving the temperature sensor on the exterior of the heat pump unit. Your heat pump needs to work longer to get rid of ice when frost conditions occur. If the sensor is in direct sunlight or is otherwise warmer than the rest of the unit, this can cause the defrost cycle to not engage for long enough. Intermittently moving the thermostat on the outside portion of the unit can help resolve the problem. If you plan to use this option, ensure that you mark the sensor’s original position so that you can adequately replace it.
Be warned however, this solution should only be used as a last resort. If all other options have failed, it would be better to call in one of our technicians at this point unless you know what you’re doing. Moving the sensor to a bad location could even lead to the defrosting process stopping, which is opposite of the desired effect. If you’re unsure of whether to take this step, simply reach out to our team instead so we can take a look at your system.
If your heat pump has frozen up for whatever reason, give it at least 4 hours to defrost itself. For freeze ups lasting longer than 4 hours, call in a service technician to take a look or follow the alternative suggestions listed above. However, If you have any doubts about troubleshooting your system on your own, we suggest you schedule a maintenance call. We primarily install and work on Bryant heat pumps and are also a Bryant dealer, but we can service many other heat pump brands as well. We look forward to assisting you!
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