one themostat for a/c and evap cooler?

cleo_bird

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!

micromind

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

cleo_bird

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!!!

micromind

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.

cleo_bird

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...

micromind

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

cleo_bird

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

micromind

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

cleo_bird

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