Heat Pump | Is Our Heat Pump Broken?
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Heat Pump | Is Our Heat Pump Broken?

This is the second time the breaker has thrown on the outside unit. This time, we noticed same day, so left it on emergency heat for 6 hours, then turned it back on. It hums – louder than normal- but the fan doesn’t spin. There is air at the proper temp from the vents. We’re above freezing, but it was colder the last time this happened and the fan spun immediately. It’s not physically seized, and there’s only what looks like a really big fuse outside, no second breaker. Pipes feel air temp. Do we have a problem?Ok, I’ll try again.A while back, we noticed the auxiliary heat was on, checked and found that the circuit for the outdoor unit was popped. Reset it, put on emergency heat, waited 24 hours, it started and ran fine (fan and all).Today, when we came home, we again noticed aux heat, and that the circuit was popped. Reset it, put it on emergency heat, waited 6 hours (since it had been only around 8 hours max that it might have been stopped), and turned it back on.The outside unit hums, but the fan does not spin. We left it on for 10 minutes before setting back on emergency heat (don’t want to damage anything by leaving it like that overnight).Could it have gone straight into defrost mode, even though it’s above freezing (but not by much)?Or is it in need of repair?Nope, the breaker doesn’t trip again immediately – it’s been about two months since this first happened.

Heat pumps are very efficient as long as the outdoor temperature is around 40 to 45 F or more. While that sounds (and feels) cold, there is still a lot of heat present in the air. When the temperature gets below about 40 F or so, it becomes more difficult for the heat pump to move heat from the outside and put it into your home. Also, since normal comfort levels are around 70 to 72 F year round, as the temperature goes down outside, there is a greater temperature difference between the inside and the outside. With a greater temperature difference there is a greater heat loss from the structure so the unit has to work longer and harder to keep up. Refrigerant is being pumped through the circuit by the compressor. The refrigerant pressure and temperature are raised substantially as it moves through the compressor. In the heating mode, the high pressure hot gases are directed by the reversing valve into the coil of the indoor unit. Air is moved by the indoor fan and passes over the indoor coil. The air is substantially cooler than the hot gases so it absorbs heat from the gases. As heat is removed from the refrigerant it condenses back into liquid. The liquid refrigerant then travels to the outdoor coil passing through a metering device. The refrigerant is sprayed into the outdoor coil at a much lower pressure and because of the reduced pressure it is capable of boiling at a very low temperature. The boiling point of the refrigerant is considerably lower than the outdoor air temperature, so when it is slightly above freezing outdoors, the refrigerant is boiling at a temperature well below the freezing point of water. Ice will form on the surfaces of the coil as the moisture in the outdoor air touches coil surfaces, even when the outdoor temperature is above freezing. The heat pump’s control board will automatically put the unit into the defrost mode every 30, 60 or 90 minutes (the time frame is selectable on the board) and the reversing valve will reposition itself to direct the hot discharge gases from the compressor into the outdoor coil. The hot gases then melt the ice from the coil. During the defrost cycle the outdoor fan will stop so the coil can get as hot as possible and melt the ice quickly. The indoor unit will typically have electric resistance heater elements that are energized during the defrost so that cold air will not blow from the vents during that time. A sensor on the outdoor coil recognizes when the ice has been melted and allows the board to return the unit to the heat cycle, repositioning the reversing valve and continueing the normal heat sequence. When the heat pump is incapable of keeping up with the heat loss because its very cold outside, the electric heaters are energized to make supplemental heat. There are 3 reasons that circuit breakers trip. A short circuit allows an uncontrolled flow of amperage to ground and the breaker overheats rapidly, causing it to trip. If electrical devices in the circuit draw an excessive amount of amperage for some reason during operation, heat builds up in the breaker a little more slowly, but the result is the same. The breaker trips and opens the circuit. Breakers have amperage moving through them a great many times during their lifetime. Each time current moves through them they heat up a little and cool down each time the current stops. Like any other mechanical device they will fail sooner or later because of fatigue. Obviously you do not have a short circuit or the breaker would be tripping every time you tried to operate the system. Electrical devices such as the fan motors, capacitors, and the compressor can sometimes develope problems that are intermittent and take time to show effects. Bearings on the motors can wear out and become sluggish, not allowing fans to turn at the correct rpm’s. The fan motor will still try to do it’s job, but it will draw more amperage than normal. Over an extended period that extra amperage can cause breakers to begin tripping. Compressors can also develope problems that will cause them to draw extra amperage. The compressor and the outdoor fan motor are fed by the same power source, through a disconnect box on the outdoor unit. Either one of them can be the one that is drawing the extra current. Most fan motors require a capacitor to allow the fan motor to come up to the proper speed quickly and to help provide a smooth running characteristic. Often the capacitor can be a dual capacitor assisting both the fan motor and the compressor to operate. If either side of the dual capacitor is bad, it can lead to tripped breakers and even failure of the fan or the compressor. I would strongly advise you to have a qualified hvac service technician come in and check out your system. He/she will know the correct methods for diagnosing any problems that exist and how to test the various electrical devices in the system. He/she will also know where to obtain the correct part or parts needed for your specific unit.


Man, I read your question over and over again, I can’t understand what you’re trying to ask…

I think you got bad compressor and/or fan motor,

Two things will cause the breaker to trip

1. An overload of current……

Typical this would happen if the compressor is drawing full load amperage, a few things that would increse the amperage on the compressor in the heating mode would be a dirty filter/ dirty indoor coil / an indoor fan that isn’t working. Sometimes the breaker will trip if there are loose connections at the breaker causing an added amount of amperage

or. 2. A short in the high voltage circuit.

if the breaker trips immeadiately after reseting it – than this is what you have – a short, and 9 times out of 10 there will be short internally in the compressor – meaning compressor replacement (not cheap).

okay…after reading what you added on..

the e-heat will only turn on if you have your t-stat set on for e-heat….or if the heat pump is running defrost…its hard to say exactly what the problem is – depending on how the installer set up the wiring for the e-heat / also the defrost shouldn’t be tripping the breaker……The only thing that comes to mind is that when the unit runs defrost the outdoor fan is shutting off (as it should) but perhaps the defrost isn’t terminating after 10 min. ( possibly defrost t-stat getting stuck/ faulty defrost board)- causing aux.heat or e-heat to come on and causing the head pressure to rise/ increase amperage on the compressor – and then the breaker tripping.

This is more less somewhat of a guess and a long shot/ probly should have someone look at it. Before calling anyone begin by checking the obvious. Filter clean / indoor coil clean – if you can see it or are able to get to it / is the outdoor coil clean……how old is the unit by the way?

Sounds like your outside fan motor is going bad and need replaced

Probably the capacitor or fan motor is bad

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