Air Pressure Switch?


Old 12-28-12, 11:45 AM
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Air Pressure Switch?

I have an older model American gas furnace. I believe the air pressure switch is bad, if I by-pass or 'jump' the wires, it works perfect, but, when connected, it will often only blow cold air or not blow any at all. My air switch model number is mpl-9300-v-0.4-deact-n/o-vs, which, of course, I can not find anyplace on line. Is there a new model that I can use as a cross reference number? If I tap on the switch, it will sometimes work for a while. Thank you!!
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Old 12-28-12, 03:19 PM
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98% of the time a pressure switch that fails to close is doing so for a reason, and it's a waste of time and money to replace the pressures swittch based on a guess.

Does your furnace have white PVC pipe to vent it or metal pipe?

The pressure switch is probably failing to close because something is plugging up the flow of combustion air through the furnace and vent. You need to check out all part of the venting system for anything obstructing it.

Do you have a multimeter and understand how to use it?
Old 12-28-12, 06:36 PM
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I have a metal piping system, its not high efficiency. I do also have a multimeter, and, have a decent understanding of it. I will check the pipes for obstruction first thing, THANKS!!
Old 12-29-12, 12:02 PM
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remove the hose from the inducer pressure port and make sure it in not plugged by inserting a small drill bit or a paperclip in there and reaming it out.

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