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Old 11-12-2007, 03:30 PM   #1
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Bad pressure switch?


I have a Carrier 58MXA060, and it wouldn't fire recently. I checked the connections on the pressure switch and everything was fine. I suspected that first because a technician had already checked it out last year and found a loose connection. This time, I noticed that one of the tubes wasn't seated completely on the hose fitting. So I played with the lines, and it kicked on. But it shut off again while I was still adjusting. I probably squeezed the tube and closed it off. So I turned off the power, and the inducer came back on. The lights started to blink the "3 1" code again, and I knew right away that it was the pressure switch. So I tapped it a couple of times and the light went from blinking to steady. A few seconds later, the igniter started to glow and the furnace fired up. Before I go and buy a new pressure switch, can I be reasonably sure that this is the problem? The furnace stayed lit and continued to run after I left the house.

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Old 11-12-2007, 11:40 PM   #2
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Bad pressure switch?


Pressure switches seldom fail. Your parts dealer may be able to test it for you. Check the vacuum hose first/also.

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Old 11-13-2007, 10:09 AM   #3
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Bad pressure switch?


Quote:
Originally Posted by undone View Post
Pressure switches seldom fail. Your parts dealer may be able to test it for you. Check the vacuum hose first/also.

What should I check on the vacuum hose? How can I tell if there's an obstruction? Should I blow compressed air through it?

There are two hoses that come off the pressure switch. One goes to the combustion intake, and the other goes comes from the collector box. I noticed the hose from the collector box wasn't completely seated onto the fitting. It also doesn't have a hose clamp. When I pushed it down farther, it made the hose bend tighter and collapsed it slightly. The furnace gave me the same "3 1" indicator lights so I took the hose off and reseated it. After a few minutes, the inducer started up, but the lights were still flashing. I tapped on the pressure switch with my finger. A few seconds later the indicator light went steady and the furnace fired up. It's been running ever since. That's why I thought the pressure switch was bad.
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Old 11-13-2007, 08:15 PM   #4
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Bad pressure switch?


I don't know the environment your unit sits. A vacuum switch (if you don't know already) is merely a diaphram inside that flying saucer looking device that, when negative pressure is applied, a micro switch is activated. I'd look for cracks and kinks in the tubing first. If you have a tube collapsing you should be able to shorten it with scissors. A cracked hose needs to be replaced (but to midigate the problem temporarily, wrap it with electrical tape). Sounds to me though, the problem isn't the vac. switch. If the manipulation of tubing doesn't get you going, you may need to check for proper vacuum from the connector at the collector box. If you have a problem here, situation may be serious.
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