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Douglas, HVAC Technician
Category: HVAC
Satisfied Customers: 3089
Experience:  Manufacture Rep for Major Brand, Technical Trainer, NATE
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My air handler runs continuously when emergency heat is on

Resolved Question:

My air handler runs continuously when emergency heat is on due to temperature drop causing heat pump to shut off. There is a 3 wire thermostat wired at the heat pump that shuts it off forcing the emergency heat to come on. We want the air handler to shut off when not heating. The heat pump is a Goodman GSH140601AA, Air Handler a Goodman AEPF 426016AA with a control board P/N B1368274 Rev B and a Honeywell TH6220C1002 thermostat. My question is should dip switch 4 be on or off. It is currently on. Everything seems to work properly when the heat pump is on.
Submitted: 5 years ago.
Category: HVAC
Expert:  Douglas replied 5 years ago.
Hi, I'm Douglas and I am here to help you resolve problems with your heating and cooling equipment.

Why would you shut the heat pump off at all?
Customer: replied 5 years ago.
My heat pump burned up a compressor in a little over a year. The professional installation people said that it should be shut off when the temperature drops below 20 degrees so they installed an outdoor thermostat that is connected to the heat pump control wiring forcing the emergency heat to come on when the heat pump shuts off. The thermostat is a 3 wire unit but is not connected to the air handler control board. The installation was installed by a local professional. They had to make 3 trips to get the thermostat wired correctly. Now I'm suspicious about their competence. I have been an electronic technician and an electrician so with some information I feel that I can do better. I've ordered a new Honeywell TH8320U1008 thermostat hoping it will be able to shut off the air handler. The heat pump shuts off the air handler just fine and I can force it to shut off by setting the temperature 2 degrees lower. 1 degree won't work. The difference I notice is a double click from the thermostat when the heat pump shuts off and only a single click when the emergency heat shuts off and the air handler continues running. I'm convinced it's a thermostat problem. This thermostat is a new one that the professional replaced thinking it could be a problem. I think that the outdoor thermostat is not installed in a normal manner so the thermostat is trying to perform a function that it is not designed to do. There aren't enough wires from the heat pump to the air handler to send an outdoor thermostat signal back. The run is quite long and would be very difficult to add additional wires.
Expert:  Douglas replied 5 years ago.
The fan is run by the G terminal, the thing they did, and who knows why because heat pumps still produce heat at 20 degrees. While it may not be enough, you would only need to supliment the heat when it gets colder. If the compressor burned up, its not because it ran in cold weather. Its because the refrigerant flow was not right, there was an electrical issue or the oil was not being returned to the compressor properly (refrigerant issue). Maybe an equipment mismatch, metering issue, or improper line set.

The outdoor thermostat they installed is proably doing nothing but redirecting the Y call at the outdoor unit back to the W Circuit. We use something like this in a dual fuel application where you cant run both at the same time, in a straight heat pump, they do run at the same time.

The only way to stop this is by adding a series of relays or by manually switching from heat to emergency heat where the fan is controlled by the heat sequencer. Heat pumps will run about 50% capacity at 10-15 degrees outside but they still draw less power per btuh by about half over strip heat so you always want to take the benifit of it.

The problem with the way they have it wired is it never really satisfies the thermostat. It satisfies 2nd stage, but not 1st stage, leaving your fan on constant.
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