Heil heat pump defrost board replacement.
- Thread starter Rnbuck01
- Start date
bazar01
Well-known member
Once the thermostat is calling for heat stage 1, the compressor/fan contactor and reversing valve should be energized with 24V. Check that first. I am not sure if Heil reversing valve is energized in heating mode though so check that too.
The defrost control board should start to work once the unit is already operational and the outdoor coil is blocked with frost.
The defrost control board should start to work once the unit is already operational and the outdoor coil is blocked with frost.
bazar01
Well-known member
Is the condenser coil surface blocked with frost and it still won't defrost?
The defrost sensor could be bad or not making good contact with the refrigerant line if you install a new control board. If there is no defrost sensor, the defrost cycle is time based.
See if the board has test pins for forcing the defrost cycle. If there are test pins, try shorting the pins and see if the unit goes to defrost mode. You should hear the reversing valve change state and start melting the frost build up. Then troubleshoot from tere on.
Yes, the condenser is covered with frost. Which pin on the circuit board does the sensor get plugged into? Does the reversing valve get 24 volts once it goes into defrost? If I jump the board and I should be getting power to the reversing valve, and if there's power there going to the reversing valve, possibly a bad reversing valve?
bazar01
Well-known member
1. Which pin on the circuit board does the sensor get plugged into? Not familiar with Heil. Does the board has a terminal that is labeled "DFS"? Check the electrical schematics on the back of the condenser electrical section cover.
2. Does the reversing valve get 24 volts once it goes into defrost? Depends of how the thermostat is programmed. It can be energized (24VAC) in cooling or heating. If you have an old thermostat, reversing valve terminal is "O" if energized in cooling and "B" if energized in heating.
3. If I jump the board and I should be getting power to the reversing valve,and if there's power there going to the reversing valve, possibly a bad reversing valve? If you jump the test pins, it should go to defrost mode and hear a swoosh which indicates the reversing valve changed state.Does the board have test pins?
Last edited:
RivennHewn
Well-known member
crabjoe
Well-known member
This is what I had to deal with today, and by 'deal with' I mean I actually had to make a call to the install company and ask for a tech to come fix it.
So what caused yours to not go into defrost?
RivennHewn
Well-known member
Didn't get a chance to talk to the tech much, just said it was an easy fix.
Defrost sensors or thermostats are normally open, closing when the coil temp drops to a certain point (typically around 28 deg F). Disconnect the sensor if you can, and drop it in a glass of icy salt water. It should close (i.e. have continuity) within about 3 minutes.
Usually I recommend replacing the defrost sensor when I do a board, just to prevent this kind of situation.
Usually I recommend replacing the defrost sensor when I do a board, just to prevent this kind of situation.
The sensor is measuring coil temperature, not outside air temperature. And usually it's located near the end of the evap coil circuit - the last place to get cold.
So, if it's measuring 28 deg at the end of the coil, the board assumes the coil is sufficiently blocked to need defrosting.
Last edited:
bazar01
Well-known member
This is what I had to deal with today, and by 'deal with' I mean I actually had to make a call to the install company and ask for a tech to come fix it.
Wow, That frost is pretty thick!
I hate working in cold weather.
bazar01
Well-known member
If the sensor is normally open, why don't you just put a jumper across the sensor wires? It will simulate the closed contacts and will force a defrost cycle. Then you will know if the sensor is bad unless the sensor is a variable resistor.