Wiring Home A/C Thermostat

[Nick1994]

My grandparents had one of those old dial thermostats that wasn't very accurate so we put a new one in from Lowe's, a non-programmable thermostat that's a Honeywell. No matter the combination of wires so far I can't get it to work correctly.

The A/C is a good size unit up on the roof and is all electric including the heater. Some configurations of the wires make it run the heat on cool and it cool on heat but I can't figure it out. The first picture is how the old thermostat was wired and the second is how it's wired now.

I don't know much about this stuff so I'm pretty ignorant on it.

We'd love the A/C to work as it's going to be 112 today and 113 all week.

Any help is appreciated!

 

[Nick1994]

Currently on "Cool" is blowing just room temperature air, no compressor.

 

[redhat]

Maybe just a thought, but put the blue wire on "B" and the red one on "R".

 

[Donald]

Make sure you do NOT toss the old thermostat in the trash if it has mercury. Thats hazardous waste.

 

[DBMaster]

Most of the stat manufacturers have a toll-free hotline for installation help. I am pretty tech savvy and reasonably smart, but there are so many variations of HVAC wiring out there that I was having trouble. The support people were very knowledgeable and helpful.

 

[Nick1994]

This configuration only runs vent, the air doesn't cool off

 

[EdwardC]

I'm not sure about the blue line, but you might need to use a piece of were to jump the R and Rc (connect both R and Rc to the Red wire).

I assume the house has a typical single AC and furnace setup.

The blue might be a common connection, you could check the voltage between the red and blue and look for 24VAC. I kind of find it unlikely that it is though.


From your picture above, I would remove the blue line and let it float, then jump the red wire between R and Rc. See if that works.

 

[Nick1994]

And these 2 configurations it doesn't even turn the unit on when on "cool"

 

[zzyzzx]

It might help you tell the difference between the white and yellow wires (old yellow and white wires can look about the same, as they do in your picture). In the old picture is the red wire making a good connection to something? It looks like it might be connected to the blue terminal.

That and with the right jumper wire(s) it's easy to get the A/C to work without a thermostat.

 

[EdwardC]

Reading the manual, I believe there should have been a metal jumper connecting between the R and Rc. Put that piece of metal back.

I'm fairly certain that's why it isn't working. The R and Rc terminals are power inputs for the Heat and cooling, respectively. If you connect the red wire to R, power can come in, connect through the relay and go back out the white wire.

If you want cooling, power comes into the Rc and out the yellow wire.

You need the red wire to connect to both the R and Rc.

 

[EdwardC]

Also, I would keep the blue line on the orange terminal, as it was. I think the O or B terminals are for a heat pump or something. I would assume that if there was something like that, you'd know, so it's probably not connected to anything, or it is the Common

 

[wymi516]

 

[scurvy]

Looking at your old setup (http://i62.tinypic.com/2rpu06t.jpg) you had, looking at the terminal colors:
Green wire -> G
Yellow wire -> Y
White wire -> W
Red wire -> ? (presumably R or Rc)
Blue wire -> O

Replicate this with your new thermostat plus a jumper across R & Rc. Do you still have the old thermostat backing plate to double check terminal letter assignments?

 

[Bebop367]

I miss wired a replacement thermostat one time.
A/C compressor & Gas Furnace both running at the same time....
Almost scratched all my hair out before getting it back right.

Good Luck

 

[Nick1994]

This is how it's wired now. I put a jumper in and tried the blue wire in O and B and regardless it still blows room temperature air, sounds like compressor or something kicks on with the fan but still blows room temperature air. Maybe I blew something in the A/C, I don't know. An HVAC company will be coming out probably tomorrow.

In the meantime they have the evaporative cooler running which is better than nothing.

Thanks guys!

 

[dishdude]

Can you pull the panel at the air handler and see what color wires are hooked up to which terminals? It's 108 outside so getting on the roof won't be too fun.

 

[Nick1994]

Originally Posted By: dishdude
Can you pull the panel at the air handler and see what color wires are hooked up to which terminals? It's 108 outside so getting on the roof won't be too fun.
Yeah, was on the roof already making sure the evap cooler pads were nice and wet. It's hot out there!

The fuse panels on it I can't see the thermostat wires, maybe they're inside the unit, I don't know. An A/C guy will be there in the next day or so.

 

[Nick1994]

Well it looks like the last way I wired it was correct, the A/C repair guy is over there now and found there is no freon in the A/C unit. He's figuring it out, but at least I know i wired it correctly lol.

 

[Nick1994]

I thought I'd update this just for the heck of it. A/C died this morning, compressor is done. We'll see if they get a new unit or a new compressor.

Evaporative Cooler is back up and running lol! 85 degrees in their house right now...

 

[CT8]

My AC quit blowing cold air then started to knock and the swamp cooler has been in use for 5 years . It gives about a 20* drop in temps when the humidity is low. It is 111* f now and the thermostat on the wall thermometer reads 84* the pool is 90*