Wire a/c with 2 wire tstat.


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Old 05-17-08, 07:09 PM
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Wire a/c with 2 wire tstat.

I an wondering if it is possable to wire my gas forced air furnace an armstrong80 to turn on the blower when the tstat (a 2 wire) is put to cooling mode. and rewire back to heating in the winter. i do not have a condensor and really dont want one, i just want the blower to come on and circulate air when it gets hot. and not when its cool. thanks for any help!
 
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Old 05-17-08, 10:31 PM
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Yes, it's possible, assuming that your furnace is also capable of being used as an air handler for a cooling system. If you can replace the two-conductor cable with a five-conductor cable it will be far, far better.

Look at where the thermostat wires connect to the furnace and then tell me the designation of all the wiring terminals. There should be R (red), W (white), Y (yellow), G (green) and C (could be any other color).
 
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Old 05-18-08, 06:20 AM
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You could rewire the stat, and switch back to it in the winter, but that is going to be hard on the wire, and may break off the ends.

be best to fish up new wire to the t-stat if you can. THen when you do wire it, you won't have to worry about switching wire every time.

I used to run the fan by the t-stat at one apt since it didn't have A/C on it, I run the fan by the Cool switch, and it would cycle the fan on and off as needed to help with the window A/C.
 
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Old 05-18-08, 03:07 PM
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With only two wires you would have to change the wiring at both the thermostat and the furnace. And Jay is correct, all that wire changing will cause the ends to break.
 
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Old 05-19-08, 12:35 PM
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Originally Posted by furd View Post
Yes, it's possible, assuming that your furnace is also capable of being used as an air handler for a cooling system. If you can replace the two-conductor cable with a five-conductor cable it will be far, far better.

Look at where the thermostat wires connect to the furnace and then tell me the designation of all the wiring terminals. There should be R (red), W (white), Y (yellow), G (green) and C (could be any other color).
yes thats whats on the furnace side. W R Y G C. the tstat has the same plus a few more, O B and some other stuff.
So how should i wire this up. i tried doing t stat R to furnace R. and stat G to furnace G, but that didnt seem to do it. Thanks!

Originally Posted by Jay11J View Post
I used to run the fan by the t-stat at one apt since it didn't have A/C on it, I run the fan by the Cool switch, and it would cycle the fan on and off as needed to help with the window A/C.

Thats exactly what im trying to do, i have a small evap cooler in the condo, does great in the main room, but it wont move air into the 3 bedrooms very well, so i pu the furnace on constant low, and it worked great. to good, made the place cold at night, so thats why im trying to set it up this way!

yes i know it will be hard on the wires, but when they break i have an even better reason to get it replaced with the right wires!
 
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Old 05-19-08, 02:10 PM
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Originally Posted by James800 View Post
So how should i wire this up. i tried doing t stat R to furnace R. and stat G to furnace G, but that didnt seem to do it.
Does the t-stat have fan On/Auto switch? And did you switch the stat to On?

Does the stat have two R? (Rh, R, or Rc?) if you do then you need to add a small jumper wire between the R.

Y-is used for cool
R- is for power
G- is for fan
W- is for heat.
 
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Old 05-19-08, 04:19 PM
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Originally Posted by Jay11J View Post
Does the t-stat have fan On/Auto switch? And did you switch the stat to On?

Does the stat have two R? (Rh, R, or Rc?) if you do then you need to add a small jumper wire between the R.

Y-is used for cool
R- is for power
G- is for fan
W- is for heat.
stat does have rh and rc, there is a jumper between the 2. there is a fan auto or on. i had i set to auto. so i went back double checked everything, and now it works....must have had a loose wire somewhere. well thanks for the help guys!
 
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Old 05-19-08, 08:14 PM
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I take that back its not working! it was only on beacuse of the const connection. it still will not turn on and off when on cool. i have the red wire stat side to RC and a jumper connecting RC to RH. that same wire goes back to the furnace and is connected to the R there. and the white wire, connected to G on the stat, and back at the furnace to G. either on auto or on for the fan, nothing happens. any ideas?
 
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Old 05-20-08, 05:12 AM
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What is the make and model of your furnace?
 
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Old 05-20-08, 09:52 AM
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Jumper R and G at the furnace and the blower (fan) should run constantly. If it does then connect the white wire to G at the furnace and then connect the red and white wires at the thermostat together and see if the blower runs. If not then then one of the wires is bad.

If that does work and yet connecting the red to the thermostat Rh (with jumper to Rc) and the white to G and the thermostat fan switch to ON does not work then the thermostat is bad.

If you want the thermostat to automatically start and stop the blower then you need to have the red wire connected to R on the furnace and to Rh plus Rc at the thermostat then the white wire connected to G at the furnace and Y at the thermostat.
 
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Old 05-20-08, 12:20 PM
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Originally Posted by Jay11J View Post
What is the make and model of your furnace?
Armstrong ultra sx80. in the manual the only thing it says about cooling is "A call for cooling from the thermostat closes R to G and Y on the blower control board, and after a short delay energizes cooling speed on the circulating blower."


Jumper R and G at the furnace and the blower (fan) should run constantly. If it does then connect the white wire to G at the furnace and then connect the red and white wires at the thermostat together and see if the blower runs. If not then then one of the wires is bad.

if i jumper R and G at the furnace, it does not blow! this seems odd to me?? shouldn't it work?


If you want the thermostat to automatically start and stop the blower then you need to have the red wire connected to R on the furnace and to Rh plus Rc at the thermostat then the white wire connected to G at the furnace and Y at the thermostat.

tried the white wire at G on the furnace and at Y at the stat also did nothing. i know the wires are good, it will still heat the house if i wire it back to normal.
 
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Old 05-20-08, 12:55 PM
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Okay, I'm going to ask several questions.

Where are the terminal connections for the thermostat wiring on the furnace? If they are in the blower compartment there may be a "lockout" switch that requires the door be replaced before anything will work.

Did you make the wiring changes with the power to the furnace on? If so you might have blown the fuse (if installed) on the control circuit. Have you tried reconnecting for heat and does it still work that way?

Do you have a wiring diagram? These are often pasted on the inside of the blower compartment door.

Do you have a voltmeter and know how to use it?

Can you take some pictures of the unit? To post pictures you need to first upload the pictures to a photo hosting site such as photobucket.com or villagephotos.com. and then post the public URLs for the pictures (or album) here. More pictures are always better than fewer. Please have CLEAR pictures and have both close up pictures and ones from a far enough distance that we can see how the various parts are interconnected. A CLEAR picture of the wiring diagram would be most helpful. Please do not "embed" the pictures to this forum but provide the URLs for public viewing.
 
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Old 05-20-08, 02:41 PM
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Originally Posted by furd View Post
Okay, I'm going to ask several questions.

Where are the terminal connections for the thermostat wiring on the furnace? If they are in the blower compartment there may be a "lockout" switch that requires the door be replaced before anything will work.

Yes there is, and the switch was pushed, and the door on.

Did you make the wiring changes with the power to the furnace on? If so you might have blown the fuse (if installed) on the control circuit. Have you tried reconnecting for heat and does it still work that way?

no i turned the power off. yes it will still heat now.

Do you have a wiring diagram? These are often pasted on the inside of the blower compartment door.

I do ill try and scan a readable copy.

Do you have a voltmeter and know how to use it?

Yes, Yes.

Can you take some pictures of the unit? To post pictures you need to first upload the pictures to a photo hosting site such as photobucket.com or villagephotos.com. and then post the public URLs for the pictures (or album) here. More pictures are always better than fewer. Please have CLEAR pictures and have both close up pictures and ones from a far enough distance that we can see how the various parts are interconnected. A CLEAR picture of the wiring diagram would be most helpful. Please do not "embed" the pictures to this forum but provide the URLs for public viewing.
ok here it is http://i280.photobucket.com/albums/k...SFIREDHEAT.jpg i know how to read some of it, but i dont under stand the hole thing.
 

Last edited by James800; 05-20-08 at 03:08 PM.
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Old 05-20-08, 04:07 PM
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Looks pretty typical to me. Red to Green should run the fan constantly.

Should read about 24 volts AC between C and R terminals with the power on and the blower door switch pushed in.

It's possible there is a built-in time delay on the fan so give it at least five minutes before determining it doesn't work. This is especially true if you are connecting the white wire to Y at the thermostat and G in the furnace.
 
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Old 05-20-08, 05:38 PM
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Take a look on the board to see if the blower motor is wired to "CONT" on the board.

If nothing on that, then you can look over to COOL, and move one of the wire to CONT, and turn power back on to see if the blower runs. If it don't then may have a bad winding on the motor, there should be another wire up on MISC, and switch those wire around and see if the fan runs.

If it runs, then move that back to COOL.

I don't know your model, i know some model CONT will run a lower speed with fan switch to ON, and if Y is called for, then blower will speed up to cooling speed.
 
 

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