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Old 04-22-2008, 02:02 AM   #1
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one themostat for a/c and evap cooler?


I have both and am looking to get a programmable thermostat. I was hoping it was possible to get one that could control both the regular a/c and my mastercool evaporative cooler. Is this possible? Any recommendations?

Thanks for the help!

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Old 04-22-2008, 08:02 PM   #2
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one themostat for a/c and evap cooler?


Assuming you want to first turn on the evap cooler, then if the temp continues to rise, bring on the A/C, you'd need a t-stat that has 2 cooling stages, and also two 24 volt relays.

One relay would control the evap cooler, the other would lock out the evap cooler when the A/C kicks in.

If you'd like a different control scheme, please describe it, and we'll help you through it.

Rob

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Old 04-23-2008, 12:50 AM   #3
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one themostat for a/c and evap cooler?


Micromind, thanks for the reply.

I guess it would be nice to have it automatically switch-over from the evap to the a/c once the temp hits a certain point, but that isn't necessarily a feature that I absolutely need.

I would be happy with a setup that would allow me to get rid of the ugly mastercool thermostat and get one programmable thermostat that allows me to choose if I want to cool with the evap or a/c. Switching it manually would be ok with me.

Can you suggest a specific model that is capable of doing this?

I have been looking at these thermostats:
http://www.prothermostats.com/produc...9&category=260
http://www.prothermostats.com/produc...1&category=260
http://www.prothermostats.com/produc...6&category=260

Would any of those 3 work?

Sorry, I'm an idiot when it comes to electrical things, so I'm trying to avoid buying something that isn't going to work for me.

Thanks a bunch for the help!!!
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Old 04-23-2008, 07:23 PM   #4
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one themostat for a/c and evap cooler?


Any of these t-stats will work. If you want to choose which system turns on, you'll need to install a switch to toggle between the two systems. I don't think any t-stats have that capability.

Assuming your A/C unit is single stage (most of them are), you'd need 1 relay with a 24 volt AC coil, and contacts that are rated to handle the evap cooler motor. You'd also need 1 single pole double throw switch, it'll only need to handle 24 volts AC, and very small current.

Make sure you have enough control wires from the A/C unit to the t-stat. If it's A/C only, you'll need 4, if it's A/C + 1 stage of heat, you'll need 5, and with 2 stages of heat, you'll need 6. If you're replacing a mechanical t-stat, there might be enough wires, one or more will be spare.

If you want it to start with the evap cooler, then bring on the A/C on further temperature rise, you'll need 2 relays, no switch, and it'd help alot if the t-stats deadband were adjustable.
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Old 04-23-2008, 11:31 PM   #5
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one themostat for a/c and evap cooler?


Quote:
Originally Posted by micromind View Post
If you want it to start with the evap cooler, then bring on the A/C on further temperature rise, you'll need 2 relays, no switch, and it'd help alot if the t-stats deadband were adjustable.
I never considered having them both running at the same time. Is this what you are suggesting?

Would this make it too humid?

BTW, this is the a/c + gas heat unit I have: http://www.colemanac.com/homeowners/...tems/index.asp

Sounds like I might be hiring a pro to do this installation...
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Old 04-23-2008, 11:55 PM   #6
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one themostat for a/c and evap cooler?


I don't think it would be a good idea to have both units on at the same time, the reason I suggested 2 relays is one to start the evap cooler when the t-stat calls for 1st stage cooling, and the other one to stop the evap cooler and start the A/C when the t-stat calls for 2nd stage cooling.

If both units ran at the same time, I'd bet the evaporator coil on the A/C would ice up pretty quickly.

Rob
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Old 04-26-2008, 03:03 AM   #7
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one themostat for a/c and evap cooler?


Rob,

I re-read your first reply and that is exactly what I want to do.
I must have missed the part about "locking out the evap cooler when the A/C kicks in" when I read it the first time.

But I am a little confused by something you said.

"If you want to choose which system turns on, you'll need to install a switch to toggle between the two systems. I don't think any t-stats have that capability."

Do I need to worry about this, or will a thermostat with 2 cooling stages and 2 24V relays do the trick?

Just trying to understand what flexibility installing the toggle switch buys me.

I really appreciate you taking the time to explain all of this! This forum is great!

Thanks,
Matt
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Old 04-26-2008, 11:54 PM   #8
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one themostat for a/c and evap cooler?


If you'd like the system to be completely automatic, a t-stat with 2 cooling stages and two 24 volt relays will do it (no toggle switch). If you can find a t-stat with adjustable deadbands, (that's the number of degrees of temperature change from cooling start to cooling stop), it'd be better. You'll likely need to play around with the deadbands a bit.

The toggle switch would be needed only if you want to manually choose which system came on when the t-stat called for cooling. A single stage t-stat would be ok here.

Rob
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Old 04-27-2008, 06:35 PM   #9
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one themostat for a/c and evap cooler?


Ok, looks like I'll be getting a thermostat with two cooling stages, two 24 volt relays, and adjustable deadbands.

You have been so helpful! Thank you very much!

Matt

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