Colemen Presidentail - intermient heat

[dave88]

Gentelmen,

Great forum. I'm having a problem as someone else had posted however, i did not want to highjack his thread. I've got a coleman presidential M# 3500a812. The A/C is working fine but heat will not come on when dammaned. It may sit for 30 minutes before coming on. I've replaced the sequencer and all other parts down stream from the sequencer (limit switches, heat elements) test fine. I noticed that I have two xformers in this unit and the sequencer has control wires(Light Blue) and (Grey) that run to a place unknown. Both xformers are outputing 24 to 30 vac.

I noticed in another post you asked if they had checked for the control voltage on the sequencer. If I do have the 24vac on the sequencer what then? If not where should I look ? I noticed the control wires run to a undetermend hiding place.

A schematic would be so very helpful!!! Thanks for any help you can provide!
Dave88

[Robert]

Look at far left side of each element for a wire connection on a white ceramic insulator that leads back to the sequencer.

See if you have 120vac to ground there and again back at sequencer.

Also look for same on far right side that goes to the limits.

Do you have 120vac to ground there.


You should have 120vac to ground at both and 240vac across them with a call for heat after 1 minute or so.


Thanks,
Robert

[dave88]

Robert,

Thanks so much...!! I see what your getting at here. Duh, I should have never assumed that just because the wires looked good that their continuity would be the same under load. I'll check for voltage as you suggeted either tomorrow or Saturday. After your adivce I'm thinking I'll find a bad connection between the wire and connector somewhere in the (elements/ sequencer) circuit. Again, I did ohm out all four fuses, both elements and limit switches, and they are good. I assume there is nothing else in the sequencer control circuit except the t-stat. Is this correct?

Being I might not get to check this until Saturday, if i do verify that I have good conections as you suggsted, with the new sequencer in mind, where might I look for the fault? Also, as i stated ealier I did verify the second xformer located in the lower heat box does have around 30 vac on it's output I did not verify that I had that voltage across the sequencer....If I do not show vac across sequencer, where do I look? Also, just out of wanting to know, is the sequencer switch only timed based or does it have a (heat senese) and time ?

Thanks again for thumping my assuming brain out of dumbville and any other advice would be greatly appreciated!!!
Sincerely,
Dave88

[Robert]

Hi Dave,

1- Call for heat at t-stat
2- 24vac travels through white t-stat wire to sequencer bottom terminals, across front and back will be 24vac. (one set will control the contacts in that stack, either 1 set or 2 sets) Bottom terminals are for a small heater that energizes main terminal s in sequence. Close first to last and open last to first.
3- When you get 24vac across bottom terminals (usually H lettered/H1-H2-H3-H4,etc), then the top and middle contacts on M terminals start to close. You'll have 120vac at each side to ground and 240vac across until they close, then get 0vac across.
4- When the main terminals close, then the 120vac goes to elements where 120vac is waiting from other side to complete 240vac circuit and energize elements.

FIRST make sure all wires are tightly connected and no breaks in the wires. Then be sure you have all needed voltages from above.

IF all is good, then either the parts are or are not working. If not, replace them. If so, then there is a leak in duct not allowing warm air to reach registers.


Hope this helps some.


Thanks,
Robert

[dave88]

Robert,

thanks so much for your help. I did the checks. I do have 120vac at both ends of both elements. and both limit switches and elements are good. I do NOT have 24vac across the control circuit of the equencer. I have verified that the xformer is good. I checked all four t-stat wires with an ohm meter and they are good. Just to verify, the switchs on the sequencer are from m1/m2 andm3/m4....? I was told the t-stat had been changed last summer. I'm starting to think my problem may be in the t-stat wiring. Inside the heat unit I have connections on the screaw terminals as follows: First screw (left to right) RC = red, RH = N/C, W = white, Next screaw i can't make out = white, G - white or yellow can't quite tale.

Again, the fan switch works and a/c works and I have replaced the sequencer. Any help is greatly appreciated!!!
Dave

[dave88]

Robert,

I traced out the control circuit for the sequencer. The w-terminal/white return wire from the t-stat has continuity from the screaw terminal to the sequencer. I then traced the other leg from the sequncer (bottom lug / light blue wire). I found it does not return to the xformer but travles through a connector that leads behined the fan...I'll await your reply before proceeding any futher. I did confirm that i do have 24vac between the white wire on top of sequencer and xformers oppsite lug. Again thanks for your help.

Dave

[Robert]

Hi Dave,

M1-M2 = one set

M3-M4 = second set

H1-H2 (at bottom = low voltage heater set

At t-stat, with it OFF, you should have 24vac across W and RH.


WITH a call for heat at t-stat, W and RH should change from 24vac to 0vac.


While you have the 24vac there, you should have 0vac across H1-H2. When you get a call for heat and W-RH change from 24vac to 0vac,,,,,at that time H1-H2 should change from 0vac to 24vac.


Hope this makes sense.

The second common wire at H2 should lead back around to eventually connect at transformer or be wire nutted or connected with another wire that does.

So need to find where that wire goes.


Thanks,
Robert

[dave88]

Robert,

Thanks for the discirption. I do understand and we are on the same path. Yep, my problem is the return to xformer. As i said, I've determend the half of the circuit from one side of x-former through the t-stat and on to the sequencer is good. The return trip back to x-former is reading about 60 to 70 ohms as seen from other side of x-former to bottom of sequencer. I've traced the wiring and it leads to behined the blower. I guess I'll have to remove the blower and whats back their.

One last question, What do you suspect of being in this circuit behine the blowerd? Are there a second (heat) relay for the blower back there? The relay in front is working and is packaged with what seems to be a couple of internal Capcitors, not sure why.

Thanks again my friend!
Dave

[Robert]

Hi Dave,

Not anything back there, may just be the wire being run that way. Only capacitor is the blower run cap on side of blower housing.



Thanks,
Robert

[dave88]

Robert,

Thanks for your help. Man, I do appreciate your time and knowledge. Your great. Now, I've got to admit that if I ever get within reach of the dumb ass person that designed this thing i swear I'll make him so mad he'll attack me so I can WHIP HIS ASS or shoot him which ever it caals for...! I've traced the circuit through three miles of wires that runs from here to a jumper and back to a jump over to another another jumper that leads to no where.

One observation i made was that when checking the 24vac I noticed i have 120vac from either end of x-former secondary to neutral. This would seem to indicate a shorted wind of primary to secondary of x-former however, the fan still works, this confounds me!!!! Any other advidce would be appreciated!

Dave

[Robert]

Hi Dave,

Be sure the meter is working and accurate. Be sure it is a 24vac secondary transformer.

IF all is good on both, then something is wrong somewhere. The blower will not work without 24vac low voltage.

IF it was 120vac, it would burn up anything it came to because all is 24vac components for control circuits.


Have you been with this furnace since it was new ? There is a lot of wiring, but what you describe sounds like someone "tinkering" over the years.


Thanks,
Robert

[dave88]

Robert,

Yep, same as you think!!!!! I'm an Electronic Tech and yes all my meters works very well. They are on the mark down to the microvolt. I've had 4 years of elecronics plus 24 years of servicing analog electronics, however, this dumb ass thing sucks to high heaven!

I've given up on the piece of trash and I've rewired it so it will work correctly...! It's running fine now but i did not think I would have to do this to a heating system,,,,,?????!!!! I've replaced the sequencer, relay and X-former. After all the repalment parts and hair pulling,,,,,????

Man, I'd like to know why in the hell (they) wired this two circuit; two thousand wire wonder piece of shit thing; the way they did? Oh well, It's done now. I'll sleep tight tonight. I'm warm!

I should have done that long ago and saved your time and my effort. Thanks again man you've been wonderful!!!!!! Only the best for you and yours!!!!!
Dave

[Robert]

Hi Dave,

You're very welcome, happy to help.


Take care and best wishes,
Robert