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Old 01-16-21, 11:05 AM   #3
jeff5may
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Join Date: Jan 2010
Location: elizabethtown, ky, USA
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I've settled on the Trane American standard defrost model for control. Works like magic. The real one starts out with model number cnt5001 and has been revised over the years. Current model number is cnt05875. Has 3 relay outputs: outdoor fan disable, reversing valve cool mode, and indoor backup heat call.

The control works off of two thermometer sensors: outdoor air temperature (OAT) and evaporator temperature. Defrost initiation and termination are dependent on the following conditions:

Initiation happens after the evap temp reaches (OAT - 25 degF) and a timer expires if you wish.

Termination depends on OAT:

OAT*****ET (degF)
>22******47
10-22****OAT+25
6-10*****35
<6*******35 or 12 minutes

There's an option 2 in the board, for rigs that are touchy around 30 degF OAT:

>30*****47
6-30****70
<6******35 or 12 minutes

I gave up on the universal heat pump control idea a few years ago. Too many people had too many different expectations, and were very centered on their own specific rig. Air to air, air to water, and water to water were the 3 main groups of people, and nobody wanted to collaborate with anyone. I couldn't find anyone to take charge of their type of system who had coding or platform integration skills, so what happened in the end was the active members all went their own separate ways.

Since then, I've found that there are a lot of preassembled controls on the market, preconfigured for all kinds of different rigs. Dirt cheap to super expensive, pick your poison. Just go on Amazon or aliexpress and search for "universal (whatever you have) control". Example: universal ac replacement control

Also, there's a super affordable, robust second hand market for r22 equipment in America. The HVAC service guy swaps out homeowner with a r410a system, and the homeowner stashes it in storage until cleanup day. I could go on Facebook marketplace today and find a 2 to 3 ton outdoor unit for 100 bucks.

Last edited by jeff5may; 01-16-21 at 11:44 AM.. Reason: Information
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