new thermostat install problem

low fan wire capped off, runs fine. Project done. for the record, @Joe417 nailed it right away.

Thanks all for the help, it caught me off guard that the wiring is opposite for Dometic and Coleman. Thought it was going to be a 5 minute project!

I would remove the low fan wire- hook it back only if the blower stops.

ok, thanks for all the help! switching the blue and red worked. I still have both fan wires tied together, the more I look into this I think different brands are different in their wiring (Dometic vs Coleman). Since I needed the +12v wire to Rc, I believe I have a Coleman AC unit.

But I don't know for sure which brand AC I have, it's ducted with an unmarked exterior cover, I'll drop the inside cover later and check for a label up there.

Once I know that, I think that will determine whether I should have the two fan speeds tied together, or just the high connected. But assuming it's Coleman, I think I should in fact remove the low speed wire.

In the meantime, it's working. My 5 minute project ended up taking a few hours and it was 90 degrees in there by the time I got it working! :S

you tube is you friend. Many videos on the very t-stat. On mine I had to disconnect the red. the problem was the t-stat wires had jumpers inside the wall and they used different color wires to get to the t-stat. You tube videos will scramble the original wiring colors.

camperdave wrote:
I'm replacing the original RVP analog thermostat with a Honeywell. The old system had 6 wires which I believe to be as follows:

Red (+12v)
Blue (-12v)
Yellow (cooling)
White (heat)
Green (high fan)
Grey (low fan)

Based on some interneting, I thought I had it figured out. Capped the 12v+, Yellow to Y, White to W, Green/Grey combined to G, and Blue to R/Rc.

It did not work... Thermostat is calling for cooling, but AC is not coming on. Any help? :)

original thermostat:


New Honeywell:

Coleman uses +12 vac to energize their relays, so just disconnect and cap the blue (-12 v or ground) and hook red to R/Rc. This will provide the +12 vac to the relays.

Did you put the batteries in?

What brand of air conditioner do you have?

With my Dometic air conditioner, when I repalced the thermostat, what you did appears at first glance to be what I had to do...but not everything is the same.

I'd suggest trying to jumper together various combinations of wires manually to see what activates what. In particular, see if tying the +12V to the fan lines activates the fans, or tying ground to them does...and likewise for the heat and cool lines. I'd expect the same to operate both, though the cooling might not go without the fan. See what works for high and low speed fans. On the Dometic air conditioner, the "low fan" wire is actually fan on/off and the "high fan" wire is actually fan speed select, so for high speed fan both wires need to be activated (grounded). Yours may be different, particularly if it's a different brand of air conditioner.

Do the instructions say you can use this thermostat on a 12 volt DC system? Your house is 24 volt AC power.

The industry standard on the new thermostat terminals is:

Red = power in
White = heat
Yellow = air conditioner
Green = fan

On the old thermostat the blue wire is "ground" providing power for the thermostat between it and the red wire. Cap off the BLUE WIRE before you short out the new thermostat!!!!!!

If this was your house:

Connecting the Red wire to Yellow would start the air conditioning compressor.

Connecting the Red wire to Green would start the fan

Connecting the Red wire to White would start the furnace.

This thermostat is not designed to support a two speed fan. Cap the grey wire.

I don't believe you can get by with tying the high and low speed fan wires together with burning something up. Were did you find the information saying this thermostat is correct for your application?

The "B" and "O" terminals are only used on heat pump applications.

Put the Red on R/RC, cap the blue, and remove one of the fan speed wires. You only want one fan speed at a time. If you want to have both speeds available, install a small single pole double throw switch on the side of the thermostat housing which you would then select manually and the thermostat would turn it on and off.(You only need small wire for the fan as the thermostat should be controlling relays.)

If you can find a thermostat with a fan speed switch built in you wouldn't have to add the switch. I have seen them but couldn't find one locally when I changed ours.

From what I remember on mine, I did color for color, and it was very easy. I am sure you do need +12 volts for a signal voltage.

I did wire my AC for high fan only.