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Old 01-29-2013, 04:21 AM   #31
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Retrofit Demand Defrost goodman clpt42


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Originally Posted by bronzemaxell View Post
mainly cheaper, comfortguru.com sell this demand defrost kit with sensors only $37, and seem like easy hack to add the o wire
The Gibson board is 38 bucks. At least thats what it cost me.

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Old 01-29-2013, 04:25 AM   #32
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Retrofit Demand Defrost goodman clpt42


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In AC mode, voltage is supplied through the O terminal. With the modded board, the O terminal will energize the RV. As these are normally closed when the relay is not active. With no voltage going to the B terminal, the board knows that it is in cooling mode and will not attempt a defrost.
An on demand defrost board doesn't go into defrost in heating mode when the outdoor temp is above X degrees(X varies with manufacturer). Pretty much has nothing to do with weather the board knows its in heating or cooling mode.
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Old 01-29-2013, 10:15 AM   #33
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Retrofit Demand Defrost goodman clpt42


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An on demand defrost board doesn't go into defrost in heating mode when the outdoor temp is above X degrees(X varies with manufacturer). Pretty much has nothing to do with weather the board knows its in heating or cooling mode.
Normally, yes. Unless you are dealing with low outdoor ambient conditions. I have run the AC in the wintertime before. Sometimes we will have a day that gets up in the 70's (like right now) and then down in the 20-30s at night. When I come home late the house might still be hot and so I'll turn on the AC sometimes to bring it back down to where it should be. I also run a head pressure control so I don't flood back to the compressor.

My parents Carrier, who I installed this board on have Christmas parties with 50 or so people over. It's not uncommon for them to run the AC in the winter either.

In both cases, while the board will never sense frosting conditions, it will initiate a defrost every 6 hours to re-oil the compressor if the board does not know it's in cooling mode. That's why it is important not to hook up the O wire to the B terminal on the board. You could get nuisance defrosts while in AC if the board gets voltage to the B terminal...
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Old 01-29-2013, 10:58 AM   #34
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Retrofit Demand Defrost goodman clpt42


Hi, Jesuitson, i saw your note that you only bypassed Low pressure contact, how about the high pressure contact?
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Old 01-29-2013, 11:35 AM   #35
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Retrofit Demand Defrost goodman clpt42


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Hi, Jesuitson, i saw your note that you only bypassed Low pressure contact, how about the high pressure contact?
On this particular heat pump there is a high pressure switch and so I did not bypass it on the board. The high pressure switch on the heat pump is hooked up to the board in my setup. If the heat pump had a low pressure switch I would have installed it too, but it didn't. I didn't want to bypass any of the safety features that were on the heat pump.
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Old 01-29-2013, 04:24 PM   #36
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Retrofit Demand Defrost goodman clpt42


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Originally Posted by Jesuitson View Post
Normally, yes. Unless you are dealing with low outdoor ambient conditions. I have run the AC in the wintertime before. Sometimes we will have a day that gets up in the 70's (like right now) and then down in the 20-30s at night. When I come home late the house might still be hot and so I'll turn on the AC sometimes to bring it back down to where it should be. I also run a head pressure control so I don't flood back to the compressor.

My parents Carrier, who I installed this board on have Christmas parties with 50 or so people over. It's not uncommon for them to run the AC in the winter either.

In both cases, while the board will never sense frosting conditions, it will initiate a defrost every 6 hours to re-oil the compressor if the board does not know it's in cooling mode. That's why it is important not to hook up the O wire to the B terminal on the board. You could get nuisance defrosts while in AC if the board gets voltage to the B terminal...
Worse that could happen when running it in cooling in the winter as far as going into defrost. Is it stops the outdoor fan for 15 to 30 seconds. The defrost it temp terminated. So it shouldn't be able to go into defrost in cooling mode since the coil is above termination temp.
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Old 01-31-2013, 12:39 PM   #37
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Retrofit Demand Defrost goodman clpt42


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Worse that could happen when running it in cooling in the winter as far as going into defrost. Is it stops the outdoor fan for 15 to 30 seconds. The defrost it temp terminated. So it shouldn't be able to go into defrost in cooling mode since the coil is above termination temp.
Well regardless it's hooked up properly as the board manufacturer intended. We can just agree to disagree on the logic of the circuit.


As an update, I too had to move the coil temp sensor. I originally hooked the sensor up where the original bi-metallic thermostat was located for the timed defrost. It was defrosting way too often. I moved the thermocouple half way up the evaporator and that solved the problem. I figure that the bottom of the coil is colder and carrier put the original thermostat there so that it would keep the defrost circuit engaged for the timer. It defrosts too often when the new system reads from this location. About half way up and everything works great...
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Old 01-31-2013, 04:52 PM   #38
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Retrofit Demand Defrost goodman clpt42


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Well regardless it's hooked up properly as the board manufacturer intended. We can just agree to disagree on the logic of the circuit.

The manufacturer didn't intend for a rely to be added, nor any alterations to the board, or wiring deviations.

It works.
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Old 02-17-2013, 04:50 PM   #39
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Retrofit Demand Defrost goodman clpt42


thank you jesuitson again
i retrofited the Rheem 47-102685-85 demand defrost board today on my gibson 13 seer 4ton

I have dual fuel furnace and heat pump,
from my 3m-50 thermostat, I use W wire for heat pump, and W2 for furnace aux, as well as O, Y, C, R wires,
i wired the gibson outdoor unit "W2" (really it is the W wire from thermostat) to B to energize the rheem board, gibson wire T1 and C to high pressure switch, also need to bypass the low pressure switch on rheem board, gibson T2 Blue wire to Y (compressor), O to O to Reverse valve.
the gibson DFT and R (red wires) not used.
amazingly, it works,
so far i run the heat pump continunouly over 2 hours, sunny, and outdoor temperature is 28F and dropping, no defrost cycle kick in yet, and no frosting on outdoor coil either.
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Old 06-11-2013, 02:47 PM   #40
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Retrofit Demand Defrost goodman clpt42


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The Gibson board is 38 bucks. At least thats what it cost me.
So this board is a drop in for Goodman without changing the reversing valve logic like you'd need to do with a Rheem board?

What's the part number?
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Old 06-02-2014, 04:36 PM   #41
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Retrofit Demand Defrost goodman clpt42


Wow, I haven't checked into this thread for quite a while. I see that many very bright people and taken my crude yet effective demand defrost board retrofit idea to a new level. Great work guys. As far as my original installation is concerned, everything is still working great, defrost only comes into play when necessary. I have gone weeks in sub 30 degree weather with no defrosts when humidity is low. Every six hours of run time the board goes into defrost for about 1 minute to make sure there are no oil issues. Great work guys. carlb23

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