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Old 05-25-2017, 02:34 PM   #1
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Join Date: Apr 2017
Posts: 3
thermostat controled a/c now!

Hi there,
if anyone was like me and looking for a way to make their a/c units work off a thermostat. I found this mod on another site and boy did it work. it cost me around $35 and about two hours but was interrupted by life during the two hours!

The simple explanation is you replace the existing furnace-only thermostat with the new one and install a relay controlled by the thermostat that acts as a switch on the A/C power line. To operate you leave the A/C turned on, with A/C thermostat turned up to maximum cooling. The new thermostat and relay then control it, and turn the A/C on and off using the setting on the new thermostat. As a bonus, the propane furnace is also now controlled by a digital thermostat.

The Great A/C Thermostat Mod - Fiberglass RV

Worked great now I enjoy summer days without the unit running constantly.

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Old 05-25-2017, 02:48 PM   #2
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Join Date: Mar 2008
Location: Southwest Alabama
Posts: 7,481
Got any pictures, makes, model numbers, etc.?

Salem 29RKSS Pushing a GMC Sierra 2500HD!
Gotta go campin!
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Old 05-25-2017, 03:12 PM   #3
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Join Date: May 2016
Posts: 235
I think they are referring to this post:

The Great A/C Thermostat Mod - Fiberglass RV
FR3 Fuelly
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Old 05-25-2017, 03:27 PM   #4
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Join Date: Apr 2017
Posts: 3
here is the link.

The Great A/C Thermostat Mod - Fiberglass RV

I was able to mount the small relay in the panel. so i didn't need to run extra romex wire as described just added the new 12v wire from the new thermostat to the relay and a small 12v ground to the ground bar in the box. Then about a 6" piece of 12ga wire from the relay to the ac breaker, pulled wire out of A/C breaker crimped on a connector to plug into the relay.

Relay - Omron #G8P-1A2T-F12VDC, (12 volt, switching 120 volt)
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Old 05-31-2017, 12:48 PM   #5
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Join Date: Jun 2016
Posts: 728
To our old camper we added a portable style A.C. unit when the roof A.C. failed. Not only was it less expensive but it already featured all of the digital style automatic controls, was much quieter than the roof one, and could be run on a 2000w generator. We perminately mounted it vented through the wall with a drain tube for the condensation. I don't think the BTU level was exactly as high, but it was close and it cooled the camper just fine. I wish they would just install this type from the factory. You get better MPG towing and have lower height clearance without that monster up on the roof. I guess the downside is you lose maybe 2 sqft of space somewhere.
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led, thermostat

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