Control through wall A/C with Nest

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Old 02-03-19, 05:15 PM
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Control through wall A/C with Nest

Hey all. Hopefully this is the right topic figured it had to do more with wiring then home automation. I have a 8k btu thru the wall ac cooling the good part of my living room and kitchen. It's a digital type but only a year old. We dont have central air but we have electric baseboard heaters with Aube relays on them connected to the nest for heating. Works fantastic. But I would like to connect the thru wall ac to the nest also so I can set schedules and maintain the temp when I'm not home. The units built in functions are limited and dont work that well when I'm gone for days at a time. Many searches online reveal people leaving them on max cool and controlling it with the appropriate relay or smart outlet. I have a 120v 20 amp 24v coil contactor ready to use on a 1900 box. Issue is my ac unit resets temp to 78 when powered off and back on. Not good considering I usually keep the house at 70. Besides rewiring the entire ac unit which I really rather not do since the added relays and rewiring for it to keep the remainder fan functions and protection will be a hassle, is there any reason why I cant just swap the thermistor on the front grille with a resistor matched with the appropriate resistance to think its permantly say 80 degrees? Then the nest will take care of the actual temperature control thru the relay. Sound feasible?
 
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Old 02-03-19, 09:05 PM
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Besides rewiring the entire ac unit which I really rather not do
This would be the best as possibly only way unless your AC allows external thermostat control.

any reason why I cant just swap the thermistor on the front grille with a resistor matched with the appropriate resistance to think its permantly say 80 degrees?
That could work, but would be easier and better to directly control thermostat part of the AC unit. Things could get complicated if it is inverting or multi stage unit. But if it is a simple single stage unit, it would not be too hard.
Do you have a model number or maybe even circuit diagram of the unit?
 
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Old 02-03-19, 10:24 PM
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Hi, it does not allow an external thermostat. The unit is a Koldfront WTC8001 thru-wall unit with heat, although I do not use the heater portion of it. I kick myself for not having a PTAC installed because I know most of those allow external thermostats, but this unit was the best choice for the pre-existing wall sleeve I had already.
Im afraid to have to rewire it as I would end up having to move all the furniture, find some help and a ladder, just to take it out of the wall again (Its mounted towards the top of a 10ft ceiling and I had to outsource some helping hands to lift it in)
 
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Old 02-04-19, 05:15 AM
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I was unable to locate the circuit diagram of your AC unit on-line.
There should be on inside of the unit.

Basically there should be a point you can connect a relay to turn the unit on/off.

When you disconnect power at the cord, does it not reset fan speed and on/off mode as well ?
 
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Old 02-04-19, 11:25 AM
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That's an EdgeStar unit. I'll post the service manual for it. Grab it ASAP as I'll not leave it up here.

PDF service manual removed. Please request if needed.
 

Last edited by PJmax; 02-05-19 at 04:56 PM.
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Old 02-05-19, 04:53 PM
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Got the diagram thanks. Guess this will be a project in the spring. Gotta pay again to have the unit pulled down but it'll hopefully save me in the long run.
 
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