Pressure switch rating

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Pressure switch rating

Postby Coper2104 » Wed Feb 27, 2013 11:26 am

I have about an 8 year old Lennox G50UH 36B 090 natural gas furnace. The local Lennox dealer wants to charge me $300 to replace the pressure switch. Since I can find them online from $24 - $50, I've decided to change it out myself. My question is - The label on my pressure switch shows a part number of 49L9001 with a rating of 0.30WC. All of the pressure switches I'm finding online through various sources with the same part number, have it listed as 0.47WC. Am I going to have a problem using any of these switches with a higher WC rating than what my original switch (with same part number) is showing?
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- Pressure switch rating

Postby Freon » Wed Feb 27, 2013 12:05 pm

Sadly you may have problems. The switches you see with the 0.47" WC will require a higher pressure from the draft inducer. It is possible your draft inducer produces sufficient pressure to close that switch but without an actual measurement, it's a gamble.

I would take the make and model of the furnace along with your pressure switch to an HVAC supply house like Johnstone or McCall. See if they have a match in their generic supply. The only other constraint is physical dimensions for a switch that will properly fit.

What makes you think the old switch is bad. Sometimes condensation or debris in the tubing to the switch can cause problems. You might try measuring continuity while VERY GENTLY applying pressure with your mouth. Check to make sure if you need positive or negative pressure before blowing. If you blow too hard you could pop the diaphragm so be very careful. Maybe you can open it to see inside and determine if it's truly broken.

Is it possible the draft inducer assembly is not producing the necessary pressure. There are other reasons for a draft inducer switch to not close.
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- Pressure switch rating

Postby Coper2104 » Wed Feb 27, 2013 12:33 pm

Thanks for responding. I guess I don't know for sure the pressure switch is bad. I'm taking the Lennox's tech word for it. When he was there, he tapped on it and got it to work and it's been working flawlessly for a couple days since he was there. I just thought I would go ahead and get the part in ahead of time in case it (or whatever) decides to act up again. I thought about taking the hose off to see if it had debris in it or was cracked, but again was waiting til it malfunctioned again. As far as the new pressure switch physically fitting, I don't forsee that as a problem as the pictures I've seen show it to be identical in every way. I may take your advice and take the switch locally and see if they can match it up to a proper 0.30 WC model. I was just so confused that the exact same switch model number being offerred today has a different WC rating.
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- Pressure switch rating

Postby Freon » Wed Feb 27, 2013 4:21 pm

I would check the hoses and everything else before it's a frigid night and the furnace stops working. If you notice condensation in the hose you might put the switch in a low 140 degree oven for an hour leaving the oven door open. There may be a little moisture inside the switch.

As a backup go find a local supply house with the switch you need so you know where to find the right one.
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