furnace comes on goes off in 30 sec repeats...


Amman air command 80. Gas noise stated sat and thought it was the blower motor but found out it was the vent blower and it went to pieces on Sunday evening. Went today and bought and replaced that vent motor. Fasco had replaced it with another model so I had to change the mounting holes but seemed to work out all right put it all back together and the burner comes on and about 30sec later the fan comes on another 30 sec it shuts the burner and fan down and starts all over again but after the fan comes on it last about 20sec next cycle about 15sec. My limiter is set at 80, 135, 200. Looked at all connection seemed to be fine. Also vacuumed it out while it was down. Appeared to have vibrated a lot before the fan went out. Any and all help is always very much appreciated. Sean snipped-for-privacy@aol.com
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perhaps the ignitor/sensor. http://www.arnoldservice.com/Troubleshooting_Heating_Problems.htm

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I don't have your furance but from what I understand, the burner turning on means that all the things checked prior to ignition should be ok. The next step is to verifiy the burner is on, prevents gas leaks, that might mean you have a dirty eye.
Now just a guess, the safe thing is to have your furnaced serviced.
tom @ www.BlankHelp.com
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Do you have a pressure feedback setup? A coworker recently had the same symptoms. His furnace monitors for pressure buildup in the vent line and will try to run but shutdown if there is too much backpressure. Turns out the installer didn't put the screen in on the outside of the house to prevent vermin from getting in. During these cold months it's an obvious entry point to your house. He had a small nest in his vent line; cleaned it out and everything ran fine. You might want to check that possibility.
Tom R

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