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Ruud achiever 90 plus wouldn't start

I had my furnace fail to start for me this morning, the fault code was 4 blinks and that means "pressure switch closed" according to the wiring diagram... but I fixed it by wiggling the pressure switch and it "clicked".  How do I keep this from happening again?  If you can help I can email Pix and a more detailed description.
Thanks
Dan

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Thanks for the carefull description of the fault, The vent system is designed so that if a leak occurs fresh air from the living space will be pulled into the vent rather than dangerous combustion gases pushed out to insure this there is a carefully calibrated -pressure switch that will not allow the unit to fire unless a negative pressure on the vent is proven this can be prevented by many things, here are a a few :a sticky micro switch, a leaking hose from the vent to the pressure sensor, cold stacking in the flu(either a down draft or extremely cold air in vent that restricts warm combustion air from being pushed out), a problem with the power exhaust fan(debris has gotten in the housing preventing an easy start), i usually find the cause to either be a bad pressure sensor hose or debris in ths exhaust fan housing either blocking blade movement or obstructing the pressure sensor hose port.
To clear the fault turn of the breaker to the unit then restart the unit and fallow the sequence of operation to see where the fault occurs the fan should come on first then the exhaust blower should come on when negative pressure is achieved it start the lighting sequence if the lighting sequence doesn't start and you get the same fault take the neg pressure hose loose from the exhaust fan housing and start the sequence again while pulling a slight negative pressure on the pressure sensor with a hand held pump continue this process until you find the fault.

Posted on Mar 11, 2008

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4 blinks is "pressure switch closed" there are 2 in the system according to the wiring diagram one for the vent system  and one for the drain system ... I just wiggled them and heard one "click" the fault light quit blinking and when I pushed the safety switch back in the furnace fired right up.  That being said is there a good website for learning how to maintain your own furnace?  I'll call a pro if I have to, but shoot I can fix a jet engine... this shouldn't be much worse.
Thanks  dan

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