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Please help with Comfortmaker GUK075N12C1 (Long)

I moved into this house a year and a half ago. We have a 75k BTU, natural gas, comfortmaker forced air furnace. I believe it is about 8 years old. Last winter when it was real cold the furnace locked out and wouldn't ignite. The inducer blower kept running. I went out to the intake and exhaust pipes to find the intake was plugged with frozen exhaust. I noticed then that the two pipes were only a couple of inched apart and only an inch or so out from the building. Oh yeah and they also terminate directly under a floor board of my deck! I got a copy of the installation manual discovered these were totally wrong.
So this year I tried venting the exhaust up through the deck. Installed an additional 90 a foot of 2 inch and another 90. Sometimes the furnace would run others it wouldn't. The length of pipe was well within the specs of the manual.
I thought maybe the pressure switch might be bad, so I changed it. Samething intermitent lock outs.
The otherthing was that maybe the condensate wasn't draining. In the past the condensate ran out the exhaust a froze against the house. Now with the 90 pointing up maybe it was choking the exhaust. So yesterday I drilled through the house about 3 inches higher up. (The highest I can go). The exhasut line definately pitches back towards the furnace. The unit ran great yesterday. I woke during the night to here the inducer blower running. I killed the power, restarted and she ran. Woke up this morning to find the blower running again. Tried the restart, no luck. Went outside and knocked the 3 inch 90 of the intake and shes fired up since. This seems like another weak attempt.
I have been told that maybe the inducer blower might be too weak and needs to be replaced. This is an expensive part. Any other suggestions?
Just for more info on these failed startups the blower starts, I hear a loud click which I believe is the gas valve but the HSI does not light.
Thanks for your time.
 

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You could have a couple different problems. The inducer motor is one. It could indeed not be running full RPM's and engaging the pressure switch as it should. That can be tested by a tech using a Magnahelic guage. The second culprit could be the circuit control board. Now, some of those Comfortmaker furnaces started using a type of Ignition and gas valve system called a "Smart Valve". The first generation ones were problem prone and aptly nicknamed "Dumb Valves". I would get a good service and inspection done on your furnace. Cheaper than continually changing parts to diagnose it.
 

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make sure you don't have any standing water in your horizontal flue line (a sagging pipe) or you might have a combustion air problem. try running the furnace with the burner door off.
 
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