I have an armstrong heat pump and am curious about how the defrost cycle works.
Rather lengthy but here it is.
The outside unit(heat pump) has a reversing valve, a defrost board, a crankcase heater, a metering device(txv or piston) and an accumulator. This is what makes it a heat pump instead of a straight air condensing unit.
When in the heat mode the outside unit becomes the evaporator and the inside unit becomes the condensing unit.Before somebody corrects me i am just stating what is different in a heat pump.
When the system goes into defrost several things happen. First the system has to call for a defrost cycle. This happens on a time and temperature sequence. When the defrost board times out for a defrost check(the defrost board has a jumper pin to determine how long before the system will check for a temperature(thermal switch) is open or closed. This switch is in the normally open position. It will close at 35 degrees(depends on the switch). This switch is located on the copper line in the condensing unit. If this switch is closed then the system will go into defrost. Now for the good part. This will shut down the outside fan, switch the reversing valve, and the outside unit will essentially go into cool mode. Because the fan is off the compressor will heat up very rapidly and the refrigerant passing thru the coils will be hot as well. This will cause the ice buildup on the outside unit to melt(defrost). This will continue until a temperature is met or it times out. Then the system will return to the heat cycle. One other thing, depending on how your system is wired the inside unit will turn on the auxillary heat while the defrost cycle is in process. That way you will still have heat while the defrost cycle is in process.
It is not uncommon for steam to come out of your outside unit while this is going on. It can also be quiet noisey sometimes.
Hope this explains what you wanted to know. If not just reply to this with any other question you have about the cycle.
Sep 14, 2011 |