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carlb23 01-11-2012 09:53 AM

Retrofit Demand Defrost goodman clpt42
Hi I am a homeowner and I have a goodman clpt42 which i installed in 2006. While the heatpump and the GMV 95 furnace have been problem free since the installation I always disliked the timed defrost feature since even set at 90 minutes my heatpump defrosts much more often then necessary. This has spurred me to change out the time defrost to a demand defrost board. Because of cost i decided to go with a White Rodgers 47D40-801 demand which i purchased from Amazon for 44 dollars. The wiring was pretty straight forward except that the white rodgers board was designed to energize the reversing valve during heat while the Goodman energizes the coil on cooling. To rectify this i just added a spdt relay to circuit so that when the board energizes the relay the relay removes power from the reversing coil, this causes the reversing valve on the Goodman to operate properly. On the original setup the yellow wire coming from the T-stat went directly to the compressor contactor, this had to be moved to the new board then the yellow out from the board to the contactor so that the board could shutdown the compressor for 5 seconds on defrost initiation. While electrically everything is working correctly, I wanted to make sure that i placed the outdoor coil temperature sensor in the correct location. I placed the sensor on the vertical liquid tube coming from the outdoor metering device just before it goes into the coil at the top. So far I haven't seen any frosting on the coils but that doesn't mean it isn't defrosting too often. I have not had the time so far to really determine how often it is defrosting but i will do that in the near future. After i am all done i will draw a schematic of the wiring Also the brown wire from the Tstat must be used to energize the defrost circuit rather than the orange wire as this board wants to see 24vac on call for heat rather than cool. If anyone has any suggestions as to the placement of the outdoor coil temperature sensor I would love to hear them. Thanks Carl.

carlb23 01-16-2012 10:23 AM


Well it has been just about 5 days since i installed the Demand Defrost Board in my Goodman heat pump.

I also installed two electronic counters so that i could determine how long and how many times the heat pump has gone into defrost.

One is a cumulative timer / hour meter that keeps track of the time the aux heat is energized during defrost the other is an event timer and it just counts the number of times the aux heat is energized during the defrost mode.

Note in my setup, when the heat pump goes into defrost is energizes a 10kw heat strip, when the t-stat calls for aux heat because the temp is below the balance point temp it only energizes a 5kw heat strip.

The white rodgers board will automatically do a short defrost cycle every 6 hours of compressor run time and so far it has logged 8 events each lasting only about 30 seconds.

So far I have not seen any frosting on the coils and while it has been dry here the temperatures have been quite cold.

yesterday the low was 18 and the high was 25 this morning it was 10.5 degrees and it is not only 20 degrees out at 11 am.

I go out and check the coil for frosting at least 4 times a day but so far no icing or frosting to the coil is present and no defrost events have happened.

The cumulative timer has only logged about 3 minutes of aux heat from calls from the heat pump for aux heat during defrost which only represents the 8 events which the board automatically does at 6 hours of compressor run time.

The demand defrost board has cut the daily energy usage from aprox 120kwh a day in 26 degree weather to less than 80kwh a day even in these cold temps.

The addition of the demand defrost is a huge energy savings at least as of now. I suspect when it gets a little warmer and a little wetter it will ice up and actually need to go into defrost but as of now i have avoided the dreaded 90 minute unnecessary defrost cycles.

With the old defrost board it would have defrosted 35 times unnecessary, based on the 53 hours of heat pump run time in the last 5 days, resulting in much less wear and tear on the compressor / reversing valve / heat strips and lastly savings huge amounts of electricity.

This simple change will pay for itself in about 1 month of usage.:thumbup:


Done That 01-16-2012 03:22 PM

I would have placed the coil temperature thermistor in the same location as the original snap-disc thermostat for the time/temp board.

The air temperature sensor is also important for demand defrost. Make sure it is hanging "free" in the unit, not touching sheet metal for example, and not near anything generating heat that would give it a false reading.

carlb23 01-16-2012 05:33 PM

The ambient thermocouple is routed to the outside of he heat pump and out of direct sunlight. The original snap disk was mounted to one of the 90 degree tubes near the bottom of the condenser coil. The new sensor is not designed to be mounted to a curved surface. So far so good, I guess I will have to wait until it actually gets some frost / ice on it to be sure the placement is ok. If not i will move it down to where the original one was but it wont fit properly.

carlb23 02-15-2012 11:38 AM


I need to move the coil temperature sensor two times since i did the install (this takes about 10 minutes to remove the fan move the sensor and replace the fan). When i located it in the original location where the snap disk sensor was located it would not go into defrost. I then moved it to the bottom of the coil on the opposite side and this caused it to defrost a little too often (when only a light frost was appearing on the coils and very little loss in performance). I have since moved it up to the center of the coil from the bottom and it has been working fine for the last month and a half.

With the sensor in this location it will only defrost when there is a fair coating of frost on the coils and the performance has dropped about 20%. The only times it has gone into defrost is when it is cold and raining or snowing or if the humidity is very high which is not often in the wintertime here when the temp is below 40. In the last month and a half it has defrosted a total of 13 times for a total time of 109 minutes. In those 45 days it would have normally have defrosted no less than 225 times for a total time of aprox 1350 minutes.

The side benefit aside from the wear and tear on the equipment and enormous energy savings the house stays more comfortable with the fewer defrost cycles.

I couldn't be happier with the modification :thumbsup::thumbsup::):):thumbup::thumbup:

Done That 02-15-2012 11:52 AM

Thanks for taking the time to share your experiences with this project, good info.

bobinphx 02-15-2012 03:46 PM

Thanks.... Now I have to go and measure how often mine is going into defrost!!! thanks... thanks a lot!!! LOL (hope you see this is my attempt at a joke)...

in all honesty, WOW is all I can say... that and great job for a non professional. Goes to show you that common sense is alive and well in the USA.

so the question comes up why didnt the MFGR do this in the first place??? why the timed defrost. Heck even my fridge does not do timed defrost... oh... I know seer rating never takes defrost into account!!!!

beenthere 02-15-2012 04:03 PM

3 to 4 inches after the OD metering device should work pretty good for sensing liquid line temp.

vhehn 06-19-2012 05:04 PM

hi carlb23 are you still around? i have a question.

arg3670 10-13-2012 10:00 AM

I'm thnking about doing the same to my goodman. I have a wiring question what happens when your on ac how does does the reversing valve get its power?


beenthere 10-13-2012 10:01 AM

The O terminal.

arg3670 10-13-2012 01:04 PM


I'm wondering if you could post wiring diagram for your retrofit on a Goodman.


beenthere 10-13-2012 04:19 PM

A diagram should have come with the board you bought. I don't have any.

dmet 11-20-2012 06:55 PM

Retrofit Demand Defrost goodman
1 Attachment(s)
I have been down about the same path as Carlb23. I used an older version (47-182684-83) and made a couple reroutes on the circuit board and glued a relay to the top to take care of the Goodman logic on the "O" pin of high on cool/ low on heat. All of this was done on the board itself, so if I ever had the Goodman dealer out, I could put the original board back in quickly (10 year warranty).
Seems to work good except that for some reason in freezing weather it will start a defrost on call for heat. It should wait for things to stabilize.
For anyone contemplating doing a conversion, there is a PDF on the internet written by Ranco. Do a search for "ranco ddl 01-03" Seems to be some you have to buy, but others post it free. Also, Rheem and Ruud and others have installation instructions with wiring diagrams.

I have wired in a switch, which is in the house where I can disable defrost altogether. I have run for days in freezing weather with no frost buildup (lo humidity), and therefore did not let it defrost. Now, I have seen things on the internet that defrosting is still necessary in cold weather to be sure lubricant is returning to the compressor. Anyone know anything about this??

My system is a DSZ18 4 ton Goodman

etona58 12-31-2012 08:38 AM

I bought the same demand defrost board as you.I want to change my timed defrost board to demand defrost. Unit is a Goodman package heat pump. Can you provide a schematic or wiring diagram of what you did to the new board?

"Now, I have seen things on the internet that defrosting is still necessary in cold weather to be sure lubricant is returning to the compressor. Anyone know anything about this??" From what I've read, some boards do a "forced defrost" every 6 hours of run time below 35* to ensure adequate oil return to the compressor.Not sure if this particular defrost board does it or not.Maybe someone with more knowledge can chime in.

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