thermostat wiring for evap cooler and heater?


Old 09-03-08, 07:44 PM
Thread Starter
Join Date: Sep 2008
Location: 80303
Posts: 6
thermostat wiring for evap cooler and heater?

I just bought a house with an electric heater and a roof evaporative cooler - each hooked up to a separate thermostat. If possible, I'd like to hook both up to one programmable thermostat - I have a LUX TX500 and 1500.

The heater has 3 wires and is currently hooked up to the LUX1500 - wired green on G, white on W, and red on RH.

The evap. cooler has 4 wires and is hooked up to an old mechanic thermostat - it has 2 fan speeds. The four wires are red, white, yellow, and green.

The LUX1500 has 7 contacts:
G, Y, W, RH, B, O, RC

The LUX TX500 has 5 contacts:
G, Y, W, RH, RC

Is it possible to hook up both to one of my thermostats? If not, can I buy a new thermostat to handle both?
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Old 09-07-08, 09:55 AM
Thread Starter
Join Date: Sep 2008
Location: 80303
Posts: 6
figured it out!

After a lot of frustration and running between the thermostat and garage to switch the power on and off, I've figured it out!

I first tried just connecting the evap. cooler wires to match the thermostat wires, in addition to the wires for the heater. This seemed to work at first, but then I realized that the controller for the evap cooler in the attic was making a really loud buzzing noise.

I thought I was screwed for a bit - I went out and bought a separate evap. cooler thermostat which didn't work b/c I realized that it's for line voltage. I checked my wires and they read 25V (which I don't understand why...). There's a controller board in the attic which gets the line voltage, and the 4 control wires come down from that to the thermostat.

Then I decided to look more closely at the mechanical thermostat that was previously used for the evap cooler. It had 2 switches for high/low fan and off/cool/vent. From looking at it, I figured out the 4 wires:
* red is the power
* pump (cool) = white
* vent (fan) = green
* high speed = yellow
Then I could hook them up to the thermostat in the proper way, instead of just matching colors (which were different).

I'm using the TX500 to control both heater and evaporative cooler! For the heater, I kept it the same:
* green to G
* white to W
* red to RH
Then I added the evap cooler wires as:
* green to G (fan)
* white to Y (cooling compressor)
* red & yellow to RC
I combined the evap cooler yellow wire with the red so it'll always be at high speed, since the thermostat doesn't have a fan speed selector. I could have just taped off the yellow and the cooler would always run at the low speed.

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