Air blend on a DGAT075BDE

Questions about repairs and parts for Coleman furnaces, air conditioners and heat pumps for manufactured homes. Click here for Coleman parts.

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minnie1967
Posts: 22
Joined: Sun Sep 14, 2014 8:05 pm

Wed Sep 17, 2014 8:09 pm

Working on the air blend system. It's a standard not deluxe. It says to check for 24 volts on the relay. But which wires? It has the 7975-3771 relay, and a rocker switch for auto or off. The rocker switch checks good continuity wise. Not knowing where the 24 volts is at, I turned the fan on auto and checked the gray wires going to the damper motor, no 110 volts. Took a chance, replaced the relay 7975-3771, damper still doesn't move/have 110 volts on it. The rocker and relay share a yellow for ground. Obviously if the rocker switch is good as long as it's on, I was expecting 110 at he motor. On the relay pin 1 is the white wire, pin 3 is yellow, pin 2 red, pin 5 green, and pin 4 gray. White, yellow, red, and green are also shared by the thermostat. Assuming I don't have 24 volt's to energize the relay. Also assuming the 24 volt's is also coming from the control board to the thermostat. Same as assuming the 110 volt's to the damper motor comes from the control board. What would be the next logical step. I would hate to toast the control board. I could assume, love that word, red and black would be the 24 volts. But, look at phone wiring, tip and ring are on the red and green, second line would be yellow and black, green can be considered ground, black can be considered ground. Too many possibility's on wiring combinations running through my head. http://postrv.com/HVAC/Gas%20Furnaces/D ... BDD%29.pdf page 21 is the wiring diagram, looks like the 24 volt source is the red wire. So I'd assume red/black power white/green data.

RH - This wire comes from the 24VAC transformer on the heating system.
RC - This wire comes from the 24VAC transformer on the air-conditioning system.
W - This wire comes from the relay that turns on the heating system.
Y - This wire comes from the relay that turns on the cooling system.
G - This wire comes from the relay that turns on the fan.


minnie1967
Posts: 22
Joined: Sun Sep 14, 2014 8:05 pm

Sat Sep 20, 2014 2:45 pm

No continuity from the red wire nut to red wire in control box, corroded wire, fixed. Confirmed now have 24 volts ac on both gray wires pin 4 relay to damper motor and secondary side of rocker switch to damper motor. I’m assuming 7681-3231 Damper Motor 24V is what I’m looking for now? I was expecting to find 110v, but it actually operates off 24vac.

minnie1967
Posts: 22
Joined: Sun Sep 14, 2014 8:05 pm

Sun Sep 21, 2014 1:39 pm

I put together a trouble shooting guide for the 24vac Standard Coleman air blend ii. The simplest check is to turn on the fan and check the wires to the damper motor for 24vac. My wires are Gray in color. In my furnace I have a transformer that takes the 120vac and cuts it down to 24vac. It's a red and blue wire. That is the 24vac feed. To the left of those wires are terminals labeled W G C R Y. (White = heat) (Green = fan) (C is common) (Red = R/H & R/C) (Yellow = Cool). So inside the blend box there is a rocker switch for auto or off and relay 7975-3771. The Black or common goes to one side of the rocker switch. On relay 7975-3771 terminal 1 is the White wire, 2 is the Red wire, 3 is the Yellow wire, 4 is the Gray wire, 5 is the Green wire. The other side of the rocker switch is the other Gray wire. The Gray wires go to the damper motor to supply the 24vac. If you turn the air blend switch off, you disrupt one of the 24vac lines going to the damper motor, turning it off, or closing the damper. My issue was I didn't have 24vac to the damper motor. I did a continuity check from the black common terminal on the control board to the wire nut outside the control box that had the black wires in it. It checked good. I did a continuity check from the red terminal inside the control box to the red wire nut outside the box, and it was open, didn't check good. I pulled the wire nut off for the red wires and the inside of the wire nut was corroded. I cleaned up the connections, put a new wire nut on, and now if I read the Gray wires to the damper motor, I have my 24vac. The damper motor still doesn't work, so the motor is shot. This is the configuration of MY furnace and is meant only as a basic guide to troubleshooting. Yours could be the same, or it could be different. As stated on the main page, if you're uncomfortable using a meter, or do not know how to, call a professional. Obviously I know how to use a meter, so it to me was a matter of reading the wiring diagram and understanding how it works. The mods may or may not leave this posted, or modify it, or move it. Many thanks to forums like this providing free bandwidth where people are allowed to ask for and get help fixing their own stuff. If it helps one, or 1000 people, it's worth it.

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