DIY digital thermostat for window A/C unit


Old 06-13-14, 11:28 PM
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Join Date: Jun 2014
Location: USA
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DIY digital thermostat for window A/C unit

Is this possible?

I have an old Maytag window A/C unit with two knobs. One controls the fan/compressor with four settings: High fan, low fan, high cool and low cool. The second know controls the degree of cooling.

Needless to say this is inconvenient - I have to adjust the knobs every so often depending on the given heat and humidity.

Is it possible to retrofit the controls and add a digital read-out so I can just set an actual temperature setting?
Maybe I can integrate something like this:
Model PLVT1 | Compact Digital Thermostat with Heat Pump Control | Dwyer Instruments
I understand this wont look as nice as a new, off-the-shelf A/C unit, but we work with what we got right?

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Old 06-14-14, 03:31 AM
Join Date: Jan 2014
Location: USA
Posts: 699
Cousin of mine had the built in thermostat go bad on an old window cooler . He had to manually turn it off and own .

I gathered up some used parts & gave them to him . A 24 VAC transformer , a mercury bulb thermostat , some 2 conductor thermostat wire and a 2 pole definite purpose contactor .

He set a junction box next to the loadcenter . With the transformer and DP contactor ( the window A/C was 240 VAC ) .

Ran power , from the circuit breaker to the j-box & tied it in to the line side of the contactor and transformer . Ran the Romex to the 240 VAC A/C receptacle to the j-box & tied it into the load side of the contactor .

He ran the 2 conductor wire from the j-box to the room , mounted the tstat on the wall , across the room from the window A/C . Tied the wire to R or R cool and Y yellow on the tstat .

Back at the j-box , one 24 VAC wire from the transformer was tied to the wire in the 2 conductor , that went to R . The wire that was tied to the thermostat Y was tied to one of the coil terminals of the contactor . The second 24 VAC wire from the transformer was tied to the secont coil terminal of the contactor .

With all this hooked up , , when the tstat called for cool , it brought in the contactor & the contactor closed . This energized the 240 VAC wiring to the A/C receptacle . The window A/C turned on .

When the tstat was satisfied , the contactor turned off & the A/C died .

He has been quite happy with this set up . He says the tstat being away from the window A/C gives him a more even temperature in the room , with the part of the room further from the A/C not being as warm . He runs the ceiling fan to distribute the cool air .

I think the xame could be done with an electronic tstat , but a third wire may be needed for the tstat if it needs a C common wire ?

God bless
Old 06-14-14, 07:57 AM
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So long as the A/C does not have electronic controls what WT outlined should work. I have seen it done before. On an A/C with electronic controls you need to bypass some internal wiring.
Old 06-14-14, 10:31 AM
Join Date: Jan 2014
Location: USA
Posts: 699
You are probably correct , the window unit my cousin has is old enough that it does not have electronic controls .

I would not try to tell some one to do this , on a newer unit with electronics .

God bless

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