coleman 7680c856 needs some help

[koyote]

Hello. Before I get going on my skylights and covering the rear deck, it's gettin chilly out.

The home we bought is a bit older, mostly well upgraded. The furnace is a coleman 7680c856.

It appears ot have all the wires going to the right places according to the wiring diagram on the unit. I have 2 immediate problems:

1: the "fan switch" is missing. I can jumper the two wires and the blower comes on. The system switch of course will turn it all off.

2: even with these wires jumpered and the fan blowing, with the pilot lit, the heater won't turn on at all. It's entirely possible that the fault is with the missing fan switch (though I can't see how).

I plan to order the fan switch today anyway, is there a suggested list of other parts I may want to order as known common problems or a troubleshooting list I can use to check for faulty parts? (I can use a meter, and have a reasonable amount of experience with basic electrics/electronics)

thanks!
Christof

[Robert]

Do you have 24vac at gas valve terminals ?


Thanks,
Robert

[koyote]

nada, nothink, 0.00VAC. there is full voltage going into the transformer.

[Robert]

Transformer: 120vac primary-line side and 24vac secondary-load side

Thermostat: with NO call for heat = 24vac across R and W and WITH a call for heat 0vac across R and W.



Thanks,
Robert

[koyote]

okay, something is not right then. I get 0 VAC no matter what, even if I diconnect the thermostat.

[Robert]

Hi,

IF you have 24vac at transformer secondary-load side, BUT not at R and W at t-stat with no call for heat, check R to good metal-unpainted ground.

IF still no 24vac, problem is in wiring from transformer to t-stat.



Thanks,
Robert

[koyote]

AHA!

Okay, I had to go to a gun show, so I'm back now (selling my knives, of course) and got to run through the last of the testing.

Transformer out to blue, blue connects to a black and red wire.

red wire to white at gas valve, 26VAC.

red to black at valve, 26VAC

red to TOP (other end of black wire coming out ot valve) of the ... aux limit? I think that's what it is. 26VAC

red to bottom (other aside of aux limit- ZERO.

jumper across that and I can turn the heat on.

so I need a fan switch and - if I'm right, the aux limit. (the lower limit is down by the transofrmer, right?)

if that's all right, I'm ready to order. and it's ready to snow. how fast can I get these?

[koyote]

of course, not HAVING a fan switch I'm left with the wonder question (since I have this shiny new thermostat) of how the fan switch works. but that's for after I have one, I guess

[Robert]

Fan & Limit Switch # 7710-3281
Lower Limit # 7660-3591
Upper Limit # 7624A3591


Call 605-229-2627 or go here and type p/n's into search window:

http://www.aberdeenhomerepair.com/store/storefront.php


Fan switch turns blower on at a certain temp in chamber box and turns it off when it cools down to certain temp at end of heating cycle.


Thanks,
Robert

[koyote]

thanks very much, put the order in just now

[Robert]

Hi,

You're very welcome, happy to help.


Thanks,
Robert