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pr1244883 05-15-2011 03:01 PM

pressure switch stuck open
I have a high efficiency Luxaire furnance, model number: G9T08012UPB13C

About a year ago the heat went out and I had to call a repairman. They replaced the ventor capacitor (and left me with a $360 bill) and said they thought the ventor motor would need to be replaced soon.

Well a year later, the indicator is blinking 3 times again which means the pressure switch is stuck open.

This time I tried to tackle it myself. I tested the capacitor and it still has a reading of 4 mfd, which it is supposed to have. I've checked all the tubes, and gently blown into the pressure switch. I can hear the switch close when I do this. I also just detached the ventor motor - which was a task in itself. There is nothing blocking the fan blades, it spins without a problem, and in general it actually looks in really good condition. With everything clean, I reattached all the parts and tried it again. I can see the ventor motor start-up and spin freely, but I still get the 'pressure switch open indicator' flashing.

The Ventor motor part number is: 373-20717-001 Ventor Assembly

Does anyone have any ideas on my next steps? How do I tell if the pressure switch is broken even if I hear the switch close when I blow in it?

Thanks for any suggestions!

Marty S. 05-15-2011 05:00 PM

Compare the inducer motors name plate amp draw to the actual amp draw. Also check the flue for blockage. If those both check fine then its time to check the draft at the pressure switch port with a manometer.

hvactech126 05-15-2011 05:02 PM

pressure switches operate on negative pressure if attached to the inducer. You need a manometer to properly check and diagnose a press switch.

pr1244883 05-15-2011 07:24 PM

Unfortunately I don't have the equipment to test the switch. Is there a way to bypass the pressure switch to see if everything would start fine??

Therefore if it did start, I would just go buy a new pressure switch.

Thanks guys

Marty S. 05-15-2011 08:47 PM

Bypassing a pressure switch is dangerous and will tell you nothing. It has either failed( which is very,very rare) or it is doing its job. Without the tools it's not diy.

Doc Holliday 05-15-2011 09:05 PM

It very well could be that he draft inducer (ventor) motor is not pulling the switch closed. This could be a weak draft motor (as your previous technican has already said, expect to buy a new one of those) AND/OR you might have a crack in the heat exchanger which would not allow the pressure switch to close. If by chance you bypass a pressure switch and if by chance you do have a crack in the heat exchanger then you may not wake up tomorrow to find out your heat exchanger had a crack.

Play it safe man, spend the money and have this diagnosed and repaired by your local service technician.

how 05-15-2011 11:55 PM

A couple of stray long shots that you can check out.
When you try firing up the furnace, does that line to the pressure switch suck or blow? If its blowing then ignore the next paragragh.

If it's sucking (negative pressure) then you should actually be gently sucking to check out the air switch rather than blowing. I seems you know how easy it is to damage those air press switches. Do a continuity test on the switch when you are doing this rather than relying on the clicking sound..

You also said you checked the lines and air switch for possible obstuctions but if it is a negative pressure line then I'd check that the port on the vent housing that the line is connected to is clear as well.

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