Ductless Heat Pumps: Troubleshooting

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Ductless Heat Pump Troubleshooting

Ductless Heat Pumps: Troubleshooting

Why does my heat pump ice up in Winter?

Heat pumps naturally ice-up in the winter. It is normal for the entire coil to be covered in a white frost and even light ice, during cold weather conditions. However, it is bad for the entire unit to be encased in ice. This indicates ductless heat pump problems which should be addressed quickly to save energy and avoid serious damage to your ductless unit. These systems should periodically go into a defrost cycle. This keeps the unit running efficiently. If the coils are blocked by ice, proper heat transfer between the coil and the outside air will not occur.

How does the defrost mode work?

When the mini split heat pump goes into defrost, the reversing valve inside of the outdoor unit is energized, switching the system from heat to the air conditioning mode. The outdoor coil becomes the hot, the indoor coil becomes cold, and both - the outdoor and indoor fans shut off. This allows the outdoor coil to melt accumulated ice. When the built-in micro-computer analyzes that all ice have been melted, the heat pump heating system goes back to heating mode.

A cloud of water vapor may be seen rising over the outdoor unit and a "whoosh" sound can be heard as the refrigerant reverses direction. The entire process usually takes up to 10 minutes (depending on conditions).

How often does the system goes into defrost mode?

Ductless mini-split heat pumps have different ways of determining when to go into defrost. The built-in microcomputer determines outdoor temperature, refrigerant pressures, and several other factors. In colder temperatures the system will go into defrost more often than in warmer.

If a ductless mini split heat pump is severely iced-up in the winter it is possible that it isn't defrosting (though there could be many other causes). Let the manufacturer certified technician check your system. Call us at 718 894-8474 or request service here.

IMPORTANT: Never pick the ice off with a sharp object. The refrigerant coils can be damaged very easily.

Why ductless mini split heat pump does not reach temperature?

In heating mode, if you set your thermostat for 71 degrees or higher and your house only seems to get up to 69 degrees - in extremely cold weather any properly working heat pump may have trouble maintaining desired temperature. A heat pump loses its efficiency and cannot keep up with the heat loss of the structure. Many manufacturers guarantee operation to 15 degrees, Mitsubishi ductless mini split systems as low as -5 degrees. This is the way heat pumps are designed to operate. Even though they don't put a lot of heat into the house and they run for longer periods of time, they are still 30% more efficient than other types of heating equipment (ICIII '08 Proceedings of the 2008 International Conference on Information Management, Innovation Management and Industrial Engineering)

If the heat pump blowing cold air:

Is the ductless heat pump really is blowing cold air? Or you, the homeowner, just think it is blowing cold air?

If the ductless heat pump really blowing cold air, i.e. it's not putting out any heat at all, this could be several things. Sometimes it could even be running in the air conditioning mode due to a malfunction.

Or you might just think it is blowing cold air. This usually happens with new ductless mini split heat pump owners. A mini split heat pump puts out much cooler air than a gas or oil furnace that most customers are used to. Furnaces tend to put out about 130 to 140 degree air, while a heat pump runs at about 85 - 92 degree. It is less than your body temperature so it feels like cold air. It is still warmer than the house so it is still putting heat into the house. Unlike a furnace that puts out a lot of heat for short periods of time, a heat pump will put out less heat for longer periods of time.

If your ductless heat pump never shuts off, runs all the time:

If your ductless heat pump never shuts off in heating mode, this could be the same as above (the heat pump blowing cold air). The homeowner just thinks it runs all the time. In extremely cold weather, a properly working heat pump will run almost continuously. If it is not extremely cold and your heat pump runs all the time, this indicates a problem. Along with this usually come a high electric bill. Let the manufacturer certified technician check your system. Call us at 718 894-8474 or request service here.

High electric bills:

Many things can cause excessively high electric bills. This includes poorly insulated home, inefficient HVAC appliances that wasting energy or it could be a mistake from the electric company. Checking these things out usually leaves one culprit - the heating and cooling system, i.e. your ductless mini split heat pump. The electric bill will be high in the coldest or hottest months. But if electric bills are higher than normal it is almost always a sign there could be a problem with your ductless system. This can range from minor things like a very dirty air filter or an iced-up outdoor unit to severe problems like a damaged compressor.

Before calling for service, check the following:

  • Outdoor unit iced-up - weather related
  • Dirty air filter
  • Poorly insulated house, air leaks
  • Outdoor coil blocked - possibly with leaves or snow drift
  • Unit sunk in ground - nowhere for ice to melt and drain off
  • Leaking gutter dripping water onto top of unit
  • Snow drift against outdoor unit
  • Open windows and drafts



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