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Old 11-08-2010, 03:08 PM   #1
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Pressure switch or other?

I have a Bryant 90 Plus MAV 350 condensing gas furnace connected to an LP source. Its 8 years old and been nothing but trouble. First was a cracked secondary heat exchanger and away we go. So in any event this year we turn on the furnace and it works fine for about 3 weeks, then we wake one morning to a very cold house. The furnace will not run. Not even the draft inducer was coming on. So first things first, I check the code and it indicates a pressure switch issue. I then check and clean all drainage hoses which are not blocked that I can see. Interestingly when I pulled off one of the 1/4 hoses that goes to the condensate pan area it starts right up. It ran two maybe three heating cycles, then the same scenario. Each time, just unplugging that one hose which runs to the condensate pan area causes the furnace inducer motor to run then immediately plugging that hose back in to the pressure switch and everything functions fine for another 1-3 cycles, then again same scenario. I kept leaning toward a blockage but can't find one and just disconnecting that one hose starts everything all over again. Any ideas? I thought about the switch, but why would unplugging the hose each time cause the switch to function again. Thanks for some advice. This is one of two 1/4 hoses going to the pressure switch. One seems to go to the combustion chamber box and the gas switch and the other 1/4 hose, the one of interest goes to the area at the bottom of the condensate tray.


Last edited by rickr01; 11-08-2010 at 03:11 PM.
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Old 11-08-2010, 05:28 PM   #2
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Post some pics of the furnace with both doors off and point to the hose you are removing. Pretty sure it goes to the collector box which is joined to the secondary heat ex. That is a differential press switch and removing the hose releases some pressure allowing it to close. Propane can burn dirty if not setup properly and foul up the secondary heat ex or it may be cracked again. The condensate trap may need to be removed and flushed with hot water and bleach.


"Cut it twice and it is still too short".

Last edited by yuri; 11-08-2010 at 05:33 PM.
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