Coleman 8900 Furnace Fan Won't Come On

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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Sun Feb 18, 2007 10:39 pm

do appreciate your help and can understand your reluctance to offer any more assistance, but if you're doubting my competence, I just retired Jan 3 from the Federal Aviation Admin after 35 yrs of radar, sonar, comm, network, & every conceivable type of electronic repair you could think of. I hold Network+, A+, and Microsoft Network certs. Just nothing on furnace repair...yet. I think I can handle any professional advice you might want to throw my direction...

Monty


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Sun Feb 18, 2007 10:39 pm

(I do appreciate your help and can understand your reluctance to offer any more assistance, but if you're doubting my competence)

What this really has to do with is the fact that I have no listing on this unit.
I believe at this time the unit is not a Mobile home furnace.
We do mobile home equipment here only.
There are 100's of HVAC stick built boards on the net but very few Mobile Home boards.
The other Stick built home boards will probably have the information you need for that furnace.
Trying to do this long distance is difficult but impossible without access to information on the furnace and that information I do not have.
You have many years of experience according to your statement but none in HVAC. While HVAC does not sound as glamorous as radar or sonar it does take some time to learn.

Once I get to a point that I do not feel comfortable with giving advice it only means that under the circumstances I feel I can help no longer. It is like trying to do brain surgery without a light. LOL

hvac1000

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Sun Feb 18, 2007 10:40 pm

Hi,

This is a MH Furnace, a newer one at that.

Below are some possible faults, could be one or more than one:

Ignition Module # 1474-0041 @ $169

Hot Surface Ignitor # 1474-051P @ $33

Fan&Limit Switch # 2845-3171 @ $14.25

Fan Relay # 3110-3301 @ $27.20

Heater Relay # 2940-3551 @ $30.36

To know which one would require systematic testing with proper equipment and knowledge of these systems.

You should first determine if Blower is ok, then deal with burner.

When t-stat calls, burner eventually ignites and blower energizes.

Burner will remain burning until t-stat is satisfied.

Blower stays on entire time and thereafter until chamber cools to preset temp.

IF you bypass/jumper fan switch, blower will run continously, but burner will go out when t-stat is satisfied.

IF burner ignites and blower NEVER energizes, you have blower/blower controls problem.

IF, when jumpered, blower runs all the time, but burner goes out BEFORE t-stat is satisfied, you have a firing rate/ignition problem.

Depending on above, you could have one or both problems, possibly something not even mentioned.

Depending on that, it could be any one of things listed or a combo of two or more.


You can jumper the Relays and Switch to determine operation or failure of those three.

The Ignition Module and HSI are more advanced and should be inspected by an HVAC Tech.

We do offer testing steps at below link for a fee, but cannot gaurantee satisfaction, as we are not there doing the testing.

Thanks,
Robert

Link: http://www.mobilehomerepair.com/Order4b.html

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Sun Feb 18, 2007 10:41 pm

Sorry for the delay Robert...Computer problems...

After advance diagnosis:

1. The TH terminal of the Ignition Module (IM)is getting 24 VAC via Roll-Out Switch via the Limit Switch & Cetrifugal Switch from the Heating Relay. So looks like the VALVE output of the IM should be satisfied (forgot to check it). I suppose it's a 24 VAC output also since it's in the secondary (24 VAC) circuit.

2. The IM is getting 120 VAC to input terminals L1 & L2(L2 is Neutral input)from the Heating Relay after it energizes. Not getting any voltage out of the IGN terminals to the Hot Surface Igniter. I have heard the HSI are high failure but should there be some resistance if checking it with a VOM. (haven't done that yet either)

Thanks for the help Robert...I know this board must have you running in circles trying to keep up with every body's problems...Monty

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Sun Feb 18, 2007 10:41 pm

Resistance of the HSI is 121 ohms. I read an open on the IGN terminals of the IM looking back at the module.

After the continuity check and having put the HSI quick disconnects back on the IGN terminals, the furnace has been working flawlessly. It has cycled on and off 3 times with the T-stat set at 68 degrees and worked as advertised. The teminals and quick disconnects appeared clean. Perhaps an intermittent IM. Most of her problems with the furnace not working has been early morning. So tomorrow morning will tell...
Thanks...Monty


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Sun Feb 18, 2007 10:41 pm

The furnace didn't come on this morning so looks like I'm back to diagnostic steps 1 & 2 above...Monty

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Sun Feb 18, 2007 10:42 pm

Hi Monty,

Sorry for delay, been away from forum since Friday.

With circuit completed and 24vac at TH terminal on IM, Booster Motor will purge the chamber for approx. 15 seconds.

After 15 second purge, Ignitor will be energized with 120vac and draw 3-6 amps.

Ignitor will remain energized for approx. 35 seconds.

After that, Valve terminal on IM will energize Gas Valve for 6 seconds.

When flame is sensed, GV remains energized.

When chamber temp is reached, Fan Switch closes and blower motor is energized.

Thanks,
Robert

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Sun Feb 18, 2007 10:42 pm

Hey Wayne,
After 24VAC at TH on the IM, Booster Motor purges, the HSI 'clicks' and energizes and glows for about 34 secs and then a 'clunk' and the Gas Valve energizes. No ignition and the HSI clicks and turns off before the 6 sec Gas Valve cycle. The voltage on the RS terminal for the FLS is at about 80-90VAC after TH gets 24VAC. Hard to determine if the Gas Valve is sticking/intermittent, the FLS is shutting the IM down, or the IM is intermittently defective. If you sit and recycle the system 6 times, it will work once or twice as advertised until the T-stat cycles and then it won't...Monty

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Sun Feb 18, 2007 10:42 pm

Make sure burner tube is clear and gas is able to get through from gas valve.

IF it is all clear, the HSI is glowing bright and receiving 120vac and drawing 3-6 amps and GV is getting 24-28vac at the GV terminals, it should ignite.

Under those conditions, if it fails to ignite, you would need to have GV manifold gas pressure tested.

These tests need to be done repeatedly until it is determined what keeps happening repeatedly.

The GV is pretty simple, if it gets 24-28vac and has correct manifold gas pressure every time, it is ok.

That would lean toward HSI or IM. IF HSI is getting 120vac, drawing 3-6 amps and glowing bright every time, it is ok.

IF you never get a burner flame then I would suspect the IM.

Hope these help. may need to call a Tech for further testing to be sure of problem.

Take care and best wishes,
Robert

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Sun Feb 18, 2007 10:43 pm

The gas tube is clear.
Will the gas company perform the gas pressure test on the GV as a courtesy?
Popped the cover on the IM and didn't see any components that had taken an excess amount of heat. Couple of signal diodes, couple of small transistors, 2 small relays, one larger one, a small NAND or NOR gate chip, and that was about it (all low current). If I was a betting man, I would bet GV but it looks like it either works with the right pressure and control from the IM or not at all with such a small window after HSI being energized.
Thanks for your help Robert...

Monty

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Sun Feb 18, 2007 10:43 pm

Hi Monty,

You would need to test all at time it doesn't work to determine what is not functioning properly.

Not sure about Gas Co., wouldn't hurt to call and see.

When it malfunctions test for those design values I previously posted.

See if GV is getting the 24-28vac.

Going to be difficult to pinpoint without all the tools/equipment to test continously and all at once.

This could be a more than one problem also.

You have what each should read when working and what each should do. IF any fail to do those things and/or produce those readings when they should, they are faulty.

If a component is receiving proper power and/or gas pressure coming in , but it is not coming out when called to do so, the component is faulty.

Take care and best wishes,
Robert

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Sun Feb 18, 2007 10:43 pm

Went thru as advised and did a complete diag on everything again twice & decided to replace the counter chip (because of the inconsistent timing for the GV & IM)(installed a socket then popped in a chip),relay supplying 120 VAC & NEUTRAL to the HSI and a thermistor on input to the Ignition Module and it appears we might have got lucky. I ordered a new HSI from you anyway as that one was old and this will take care of her for quite a while. Thanks for your help Robert. You guys provide a really cool service...Monty

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Sun Feb 18, 2007 10:44 pm

Hi Monty,

You're very welcome, glad it helped and hope she keeps you warm for many more cycles.

Due to length of this thread, I'm going to lock it off.

If more questions/info needed later, please start a new thread.

Take care and best wishes,
Robert

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