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Old 03-26-2010, 06:48 AM   #1
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Adding a thermostat to an AC

I have a Duo Therm Brisk Air, is it possible to tie in a wall thermo to it?
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Old 03-26-2010, 08:41 AM   #2
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It might not be a big deal, but the new rooftop coolers don't provide for external connections. You should have schematic, probably glued to the inside of the diverter cover (the inside piece). Take a photo of it.

Zep
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Old 03-26-2010, 11:19 AM   #3
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Originally Posted by LI Pets View Post
I have a Duo Therm Brisk Air, is it possible to tie in a wall thermo to it?

if this manual covers your air conditioner, there is a thermostat built into it. It is the handle on the right that is labeled colder. The thermostat controls whether or not the A/C is running or not, and it appears that the fan is wired to run continuous whenever the left control is in any position. That is the way the A/C in my old trailer worked.

Since you question is "is it possible", the answer is yes, but it would require internal modification and added parts inside the control circuitry of the unit.

My opinion is that is it not practical.

Regards,

Ken
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Old 03-26-2010, 12:42 PM   #4
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Quote:
Originally Posted by LI Pets View Post
I have a Duo Therm Brisk Air, is it possible to tie in a wall thermo to it?
Quote:
Originally Posted by w7ts View Post
if this manual covers your air conditioner, there is a thermostat built into it. It is the handle on the right that is labeled colder. The thermostat controls whether or not the A/C is running or not, and it appears that the fan is wired to run continuous whenever the left control is in any position. That is the way the A/C in my old trailer worked.

Since you question is "is it possible", the answer is yes, but it would require internal modification and added parts inside the control circuitry of the unit.

My opinion is that is it not practical.
Bob,

If Ken's wiring diagram "fits", then you "could" connect a line voltage wall mounted thermostat like this one, Amazon.com: LV3 Lux Products Line Voltage Cooling Only Single Thermostat: Home Improvement , with a piece of 12/2 NM wire.

My issue with this type of control system is that the external 'stat only controls the compressor, and not the fan, too.


We have a Dometic AC that works similarly. Dometic offers a different control package that works and is wired (low voltage 'stat) like your home system. The new control parts are about $150 at a guess.

The downside there is that if you have a resistance heater in your unit, too, (like we do) the "new" controls are not compatible with the heater, so you lose the heater.


I agree with Ken, the results you achieve may not be entirely practical....

best,
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Old 03-26-2010, 01:10 PM   #5
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Let me double check - I could have sworn my AC unit on the Classic was connected to my Thermostat in the bed room...

I'll get back with everyone...
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Old 03-26-2010, 01:16 PM   #6
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Let me double check - I could have sworn my AC unit on the Classic was connected to my Thermostat in the bed room...

I'll get back with everyone...
Hi,
You don't need to check. It is connected to the thermostat. However it was designed to used that way. It is a more complicated unit and was designed to be used with the comfort control (thermostat).
Hope you enjoy your new trailer.. We sure like ours.

Regards,

Ken
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Old 03-26-2010, 06:56 PM   #7
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Not easily

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I have [a modern air conditioner], is it possible to tie in a wall thermo to it?
My vintage air conditioner has a wall-mounted thermostat just like you mentioned. More than likely, the thermostat was an off-the-shelf item available in 1967 for home air conditioners. Modern wall-mounted thermostats still work more-or-less like this one.

Home AC thermostats depend on controlling the flow of power to the energizing coil of a 24 VAC contactor whose main contacts control the power to the compressor.

My Armstrong AC has a 24 VAC transformer built in to provide power for this application. Modern day units do not.

Modern day units switch the compressor's primary power directly through the built-in, specially-designed thermostat. It is doubtful that you will find a wall-mounted thermostat rated to cycle such a load.

What you would like to do is possible, though. I ran into a similar situation this winter after a pipe froze & burst in unheated my shop. After repairing the damage, I looked for & found a wall-mounted thermostat with a lower temperature rating of 35 degF, i.e. it would keep the place just above freezing when necessary.

An apppliance repair shop sold me a transformer, and my toybox yielded a contactor appropriate to the heating load. Similar components would be required for your cooling application.

Tom
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Old 03-26-2010, 07:18 PM   #8
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Modern day units switch the compressor's primary power directly through the built-in, specially-designed thermostat. It is doubtful that you will find a wall-mounted thermostat rated to cycle such a load.
actually Tom, 22 amps is likely to be enough....

Lux - Mechanical Thermostats: LV3-1042

also, Bob, you can find the conversion parts thru Dometic for the Brisk Air here - Spare Parts - Dometic

or some more info here - Operation & Installation Manuals - Dometic


best,
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Old 03-26-2010, 07:27 PM   #9
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actually Tom, ...
Excellent! LIpets will be ready to go.

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Old 03-26-2010, 07:38 PM   #10
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I have a Duo Therm Brisk Air, is it possible to tie in a wall thermo to it?

Bob, I think if you will PM nickcrowhurst he can tell you how to accomplish it. I was going to add one to the AC on my first unit but traded before I did it. He told me how, but I have long since deleted his e-mail.
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Old 03-30-2010, 06:06 PM   #11
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Bob, I think if you will PM nickcrowhurst he can tell you how to accomplish it. I was going to add one to the AC on my first unit but traded before I did it. He told me how, but I have long since deleted his e-mail.
Here we are, from 2004, one of the best comfort improvements I've ever made to the Airstream, and still not a problem with it since then:

http://www.airforums.com/forums/f427...ace-14953.html

Nick.
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Old 03-30-2010, 06:37 PM   #12
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Thanks for all the input, I was traveling and just returned.

I'll look thru all this info.
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Old 03-31-2010, 09:44 AM   #13
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The thing to watch with line voltage thermostats is that, with a heavy load, there is a certain amount of resistance heating in and around the thermostat from the current flowing through the wires. This leads to poor control. With A/C what will tend to happen is that there will be a fairly wide temperature delta between the "on" and "off" points since after turning "on" the thermostat warms up and thinks the room is warmer than it really is.

Unless you're in a dry climate you want to set up the A/C so that the fan runs all the time, because that will help keep the evaporator from freezing up.

The relay setups described upthread are the way to go. Be sure that the relay is sized so that its inrush rating exceeds the LRA (locked rotor amps) of the compressor or you'll end up with the relay contacts welded together at some point.
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