Honeywell Thermostat Mod Problem

[rockfordroo]

Originally Posted by Bama Rambler

Actually Dometic controls the functions on older units by switching the negative not the positive. So, the green needs to be hooked to RH/RC and the red taped off. The red was used to power the internal relays, but now the batteries do that job, so no need for the red.

X2. Forgot about that.

[Boilermaker59]

Originally Posted by rockfordroo

Not totally; comparing your pic in post 11 with my PDF, the first 3 are the same:

Wire color Boilermaker Mine
Red 7.5 vdc 12 vdc
Yellow Cool Cool
White Heat Heat
Blue Hi Speed Ground
Brown Lo Speed N/A
Green Ground Hi Speed
Gray N/A Lo Speed

Yes, I realize the some of the colors are the same.

[rockfordroo]

Well, it seems clear that your wiring is incorrect. I suspect you may have to follow the wiring to figure out which wire does what.

[hd0187dh]

Ok. Easiest way to check that is to disconnect the yellow and touch the green to the yellow wire. If the compressor comes on then cap the red and attach the green to RH/RC and put the yellow back on Y

[Boilermaker59]

Currently I have the brown and blue going to G on the Honeywell. It was my understanding that I needed both of these wires to put the fan in high speed. i.e it only uses the brown wire for low speed, but both for high. Is this incorrect? Do I only need the blue wire in G? I'm trying to avoid using a switch to control fan speed.

[hd0187dh]

You don't want to put the blue and brown together. That will burn up the fan motor. You don't want to power both speed taps at the same time as it will over heat the motor windings.

[Bama Rambler]

Originally Posted by hd0187dh

You don't want to put the blue and brown together. That will burn up the fan motor. You don't want to power both speed taps at the same time as it will over heat the motor windings.

While that's true for Coleman, it's not for Dometic. They use some "interesting" relay logic. In order to get high fan speed, you have to have both fan wires at the thermostat hooked together.

[hd0187dh]

Wow. Ok. Any other DC motor would eventually burn up with both speed taps energized. That's interesting

[Bama Rambler]

You're actually right about not energizing both speed windings in the motor, however, the wires at the thermostat aren't going to the motor windings. Dometic placed two relays in a series/parallel type arrangement (for lack of a better description) in the control box, so in order to get high speed to run you have to energize both relays.

[hd0187dh]

I know the low voltage t stat wire go thru a relay that controls line voltage to the blower motor. I've just never seen a 2 speed motor that needs both speed taps energized to run at hi speed. I'd love to see a schematic of how the line volt side is wired.

[rockfordroo]

"I know the low voltage t stat wire go thru a relay that controls line voltage to the blower motor. I've just never seen a 2 speed motor that needs both speed taps energized to run at hi speed. I'd love to see a schematic of how the line volt side is wired."


I don't think it uses both windings energized at the same time. It uses both RELAY's energized at the same time. When energized, the first relay supplies 110VAC power to the second relay. That 110VAC power runs through second relay when it's de-energized, to the low speed fan motor winding. Energizing the second relay transfers the power from the low speed winding to the high speed winding.

So energizing the first relay runs the fan in low. Then energizing the second relay shifts it to high.

So putting both relay wires on the same T-stat connection would energize both relays at the same time, and there would always have the fan running in high whenever that T-stat connection was "turned on."

Here's a "possible" schematic:

[Boilermaker59]

Final update. Took the camper out this weekend, and the thermostat worked perfectly. I had it wired right from the beginning. It was in fact the compressor safety feature that blinks "cool on" for 5 minutes. Basically it doesn't allow the compressor to turn back on for five minutes after it turns off. I'm not sure why, but it seems like everytime you take the batteries out, it goes through this safety cycle. I just wasn't being patient enough. After that, worked fantastic!

[Bama Rambler]

Great news! Thanks for coming back and letting us know that it worked well for you.

[hd0187dh]

Great !

[Fly YX]

If you put the red and the yellow wire together the compressor should kick on. Sorry just delete this did not see the rest of the posts
Glad you got it going