Wiring a digital thermostat to control window unit air a/c

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Wiring a digital thermostat to control window unit air a/c

Postby aggie79 » Mon Apr 25, 2016 1:26 pm

After about 9 years of service, it appears that my first generation PetCool air conditioner is on its last legs. I want to replace the PetCool with a 5000 btuh window unit. Many teardrops have permanent or temporary window unit air conditioning installations. What I would like to do is however something that I haven't seen on this board.

I want to mount the window unit in my tongue box and control it with a residential-style digital thermostat (non line voltage and non-programmable). My plan - at least for now - is to "hack" a manual thermostat window unit. I want to be able to separately switch/control the blower and the compressor/cooling fan from inside the teardrop with the thermostat.

With my minimal understanding of electronics, I know that I will need the thermostat, an electrical relay to switch the blower, an electrical relay to switch the compressor/cooling fan, and transformer(s) to power the themostat and relays. My questions are:

1. What type and size of relays should I use?
2. Can/should I power the thermostat and relays with the same 120V AC to 24V DC power supply? If so, what size/type power supply should I use?
3. Is there an RV thermostat that is powered by 12V DC but can switch 120V AC that could be used instead of #2 above? (Same for the relays).
4. Does anyone know of a schematic that shows what I would like to do?

While I feel pretty good about my wiring abilities, I don't have experience or education in electrical design. Thank you for your suggestions and comments.
Tom (& Linda)
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Re: Wiring a digital thermostat to control window unit air a

Postby lrrowe » Mon Apr 25, 2016 1:38 pm

Tom, I have no idea how to design this. But I am very intersted in what responses you will get.
Bob

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Re: Wiring a digital thermostat to control window unit air a

Postby Shadow Catcher » Mon Apr 25, 2016 2:06 pm

I was originally going to go digital but chose the wrong thermostat. So I pulled the one out of the Frigidaire along with an on off switch, stuck it in a project box and ran wires through the air outlet hose.

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The one thing I did not put into the project box is the speed control which I left on the AC unit.
You should be able to take your hint from the wires in the AC. One problem you may however run into is that there is physical switch/relay and I have no idea what the amperage is that it handles. I was looking to upgrade my heater and AC to an RV type thermostat and finding they are dependent on the relay in the AC.
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Re: Wiring a digital thermostat to control window unit air a

Postby aggie79 » Wed Apr 27, 2016 5:28 pm

Seems like my original idea was another case of over-thinking and coming up with a complex response to a comparatively easy solution. :?

:thumbsup: :applause: I never thought about relocating the control panel components.

I'm guessing the electronic/touchpad control units are more touchy about extending the wire length than the ones with selector switches.

Now I've need to figure out how to fit the AC in the tongue box and duct the supply air and possibly the return air.
Tom (& Linda)
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Re: Wiring a digital thermostat to control window unit air a

Postby Shadow Catcher » Wed Apr 27, 2016 8:07 pm

The original thread is here http://tnttt.com/viewtopic.php?f=30&t=44561 I ran into a problem with icing caused by too little air flow which because of goes into and come out of hoses size. the solution in my case was the 12 bilge blower with a PWM speed controller. Others if you read the thread have increased hose size and not had the problem.
In our case the hoses enter at the foot of the bed and are directed with standard RV fittings upward. We also run the two computer case fans on medium speed in our vent to keep the coolth distributed.
One reason I did not want to mount the AC permanently is because I wanted to be able to leave it home and physically isolating it which means it is virtually silent. And the condensate has to go some where and most of the small AC are slingers, I drilled a drain hole because I do not like sound of the fan hitting the condensate.
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