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Ol'Jim 12-29-2007 10:45 AM

Coleman Gas Furnace - Freezing, Need Help!
I have never seen this malfunction before. Anyone experienced anything similar? Appreciate any & all thoughts on it.
Coleman Series 90, Model 2960-666 (Approx 1993 vintage, household High-Eff unit). T-Stat demands heat. Draft Inducer activates. Direct-Spark Igniter fires Main Burner (no pilot on system). Main Blower kicks on normally. Runs properly for around 5-10 minutes. Then starts making a noise similar to if you tossed a small rubber "super" ball into a clothes dryer. (Intermittent & varying "ping" or "pong" sound) emanating from vicinity of draft inducer. The vacuum switch starts clicking in unison with the pinging. Eventually, the Fenwal box, (Ign Control, which also controls gas valve & receives the input signals from the Flame Sensor & Vac Switch), detects enough erratic vac sw signals that it cuts off the gas valve. Draft Inducer continues to run. Fenwal box re-sequences and re-lights the burner, which runs only a few minutes at this point, then stuttering vac signal causes Fenwal box to go into lockout with draft blower running. If I cycle T-Stat or Power shortly thereafter, same failure occurs. If I let it sit for about 1 Hr, then runs normally (no noise, solid vac signal) for approx 5 min. Measured vac signal at port of draft blower, it is steady until noise begins, then fluctuates wildly. Replaced Draft Inducer with known good one, same thing. (UPDATE: Basically NO vacuum from inducer port, until I let system "rest" for 20-30 min). Ran snake thru exhaust tube, then put Shop Vac on outside outlet, no debris or sign of problem. What could suddenly cause vacuum to go nuts, then back to normal again? Any ideas? Cleaned flame sensor, going to replace all condensate drain hoses this morning. It is around 18* outside, and 50* inside, (after restarting furnace 10 times). BRRRR- Thanks guys. Baffled by this one, none of my local fellows has seen it before... -Dan (Jim) Moore.

Summit Heating & Air 12-29-2007 11:40 AM

What you're describing sounds just like a condensate drainage problem. I'd clear every hose and go from there.

Ol'Jim 12-29-2007 01:44 PM

Summit - Thank you for the reply, I suspect you are dead-on right. I removed all plastic drain lines, (pretty cruddy looking, some really loose-fitting). Have cut new hoses to fit, but before I put it all back together, I noticed the 2 small steel drain nipples that exit at bottom of burner cabinet were dripping very slowly, and the drainage was a bit rusty-looking. So I attached a piece of the new hose to each of them, and tried to blow through. One side is basically clogged, and I can barely move any air through other side. As I did so, I could hear slight bubbling of water inside unit. As these 2 drains handle all of the condensate from the secondary Heat Exchanger, I would imagine they should flow a bit more freely than they do. Tried pushing (gently) a piece of wire up the drains, it passes about 2 inches up and stops. This is about where they enter the bottom of the HX. Do you know if there is any type of trap or baffle on the other side of these tubes? (Where they enter the HX). I don't want to force anything, unless I know it is safe to do so without causing damage to the unit. I cannot find a manual or cutaway view of this Coleman unit online anywhere. Because they drain the HX, I don't imagine they should be wide-open, but I am wondering if I can try to clear them using stiff wire? Appreciate any expertise you can share. Thanks, -Jim.

Summit Heating & Air 12-29-2007 06:22 PM

Jim, you can try to use stiff wire. Often times just loosening it up with a piece of wire will get the job done. It usually wont take much to clear things up. I dont know about any kind of baffle behind the tubes, probably not. Once you get the hoses disconnected, clearing them is pretty straightforward. Sounds like you're on the right track.

bigMikeB 12-30-2007 08:01 AM

I'm not that sure about Coleman but many units actually have a small fin coil (secondary heat exchanger) tied into the lower end of the primary exchanger.

rlbagb 12-30-2007 11:10 AM

Coleman Funace model#2960
Hello, My name is randy from greenville,mi and I have the same coleman furnace as you, the series90. I also have the install manual and furnace brochures on this model! I have problems some times with this model with the condensation and such. Anyway the reason I have respond to this post is
because I believe I can solve your problem. Last year I had this problem with
my furnace, The problem I believe is the blowerwheel/motor that plugs into the vaccum switch. My blowerwheel had shattered and thats why the vaccum
switch kept shutting down. I also believe this is your condensation problem!
Anyway, I hope this info can help you out and good luck!:)

rlbagb 12-30-2007 12:38 PM

2nd heater exchange
Hello, This is randy again from greenville, mi. I wanted to add some info on
the condensation that comes from this furnace. As you notice the condensation comes down the tubes from the blowermotor, it travels down to the base where the other tubes connect to the heater exchanger (radiator) it pulls in the condensation in the right tube(facing the front of furnace) then it exits from the left at a slow pace.
Thats why it seems that the HX is plugged up! On mine I have a condensation box (Pump) when it fills up, The pump kicks on to pump it outside.

bigMikeB 12-30-2007 01:06 PM

Can you give a more complete model number? It should be like FC9C-DH or FC8V-UH or something in that type format. There is a recall on some units. With a complete model number I can find out from my supplier on Monday.

Ol'Jim 12-30-2007 11:21 PM

Big Mike,
The complete Model # is 2960-666. I am aware of the recalls on Coleman Mobile Home models (DGAT 070 & 075, I believe). This unit is a regular home upflow version.

I do appreciate your posts. I replaced the draft inducer (combustion blower) 2 years ago, due to the same problem you had. The plastic wheel shattered. I bought a Fasco A088 which is a direct replacement for the Coleman P/N. Kept the original blower, and bought a new wheel for it for a few bucks. Came in handy in troubleshooting this problem. I would be very interested in purchasing a couple of specific page scans from your Coleman manuals, assuming there would be no legal repercussions about copying old obsolete technical data... Would you please e-mail me at when you have a chance? Thanks!

GOOD NEWS! As I write this, the inside temp has reached 68*, (Oustide temp = 20*). I owe a BIG Thank You to all, especially Summit Heating & Air, for his input and advice. It was indeed a condensate drainage issue, the 2 drains on the secondary Heat Exchanger were clogged. I removed the main blower, and slid into the blower cabinet, and saw the drains had almost a 90* bend in them. So I formed a 4" piece of heavy wire into a curve, and pushed it up into the drain tubes. Cleared them out, and nearly filled a 1 quart water bottle with what came out of there! Installed new drain tubing throughout system, and it is now working perfectly!! THANKS GUYS!! I cannot properly express my true appreciation for your willingness to share experience and wisdom.
My best wishes for a happy, successful, safe and healthy New Year to all of you and your loved ones, and may God Bless you all. -Jim.

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