New Pressure Switch or Draft Inducer?

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Old 12-09-10, 03:59 PM
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Question New Pressure Switch or Draft Inducer?

First off this is my first post on here and I just wanted to say thanks in advance for any help. I have a Comfortmaker RPJ Heat Exchanger 80,000BTU Furnace. Not sure of the specific model #, it was pretty long on the label inside the unit.

Anyways,

Basically at times when the furnace is off for awhile, like at night sitting with the temp on the thermostat down, the unit will just stay off. I go down to it, tap the inducer motor or rubber line running to it from the pressure switch, and it magically starts the inducer motor and heater starts working again.

Today I noted the 2 blinks error light, which my manual says "Pressure Switch Stuck Closed" - I am not a major furnace tech, but I do know cars and pretty elaborate mechanical stuff, so this to me is one of those things I'd like to fix myself.

Do you recommend I buy a new draft inducer assembly or a pressure switch? Does the draft inducer basically kick the pressure switch when it sucks in the air? Thanks for any help you can offer, I am tempted to post a picture so you can see my setup and give advice. I appreciate all your time.
 
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Old 12-09-10, 04:06 PM
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I recommend that you first pull the rubber tubing from the pressure switch AND the nipple on the induced draft fan housing and thoroughly inspect the tubing for cracks and deterioration.

Then, using an appropriately sized drill bit make certain the hole through the nipple on the induced draft fan where the rubber tubing connects is completely clear. Put the tubing (or replacement if the original is bad) back in place and test.

It is not uncommon for the nipple to corrode internally and close off the connection to the pressure switch. The pressure switch itself rarely fails.
 
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Old 12-09-10, 04:18 PM
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I blew out both ends of the hose and also the nipple on the tube/elbow on the draft inducer. They are all clear, the only thing left is to replace the hose then see whats what. Thanks buddy for the suggestion!
 
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Old 12-09-10, 04:25 PM
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The inducer motor should power up and come up to speed whenever the thermostat calls for heat. I take it that's not happening reliably.

If so, you need to determine why the inducer motor is not starting reliably. I'd start be using an AC voltmeter to verify that you have 24 VAC at the W terminal when the inducer motor isn't starting. If you do, the thermostat is switched on.

Next I'd verify that you have 120 VAC to the inducer motor. If you do, you probably have a motor that's not starting properly.

If you have 24 VAC at W and no voltage at the inducer motor, you probably have a circuit board that not switching the inducer motor on properly.
 
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Old 12-10-10, 09:33 AM
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Just saw the second response, have not been home, but this morning the 2 blinks was happening.

I went down, unhooked the rubber line from the draft inducer and blew in it. Basically I blew into the pressure switch. From there the draft inducer fired right up and it started working. What does that tell me? I guess I thought the draft inducer made the pressure switch work. Any help is appreciated. Thanks!
 
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Old 12-10-10, 09:55 AM
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You are correct. The inducer motor fan creates a negative pressure in the furnace heat exchanger. When that negative pressure is great enough to circulate the combustion gasses through the furnace safely, the pressure switch should close.

It's possible some relay is hanging up and not turning the inducer motor on and that jogging it while working on the furnace caused it to close.
 
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Old 12-11-10, 10:29 AM
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I need to correct my last post, I actually sucked on the rubber tube to pull the air out of the pressure switch, then the draft inducer magically turned on. Not sure if that changes anything, thanks!
 
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Old 12-11-10, 11:57 AM
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No, it doesn't.

The pressure switch closing is a RESULT of the inducer motor running, not a cause of it running.
 
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Old 12-12-10, 07:53 AM
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Just had a tech out, he put a meter on the rubber tube that runs into the inducer motor, no suction out of it at all. He was stumped and has to call comfortmaker because he said a bunch of things seem weird.....

He said it may be the switch, but he doesn't understand why certain wires running to the inducer motor are 24 volt but they should be 125 volt or something, I dunno honestly he was as confused as me. He says comfortmakers are tough to work on and they do weird things on them when they build them...

So I am hoping it is a good thing I didn't just throw parts at the furnace, but they are gonna charge $235 just to change the pressure switch which I know I can do for under $100. But then that might not be it, I am totally confused!
 
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Old 12-12-10, 08:19 AM
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Well, I give the guy credit that he HAD a manometer, and actually used it. Unfortunately and surprisingly, he didn't seem competent to understand how to interpret the results.

The pressure switch is the problem only 5% of the time. It's a waste of money to change it out until a competent person has diagnosed the problem.

Was the inducer motor running when the repairman found no negative pressure? If it was, I'd start by taking the rubber tubing off the inducer motor housing and using a small drill bit to clean out any corrosion or debris that might be plugging that small hole.
 
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Old 12-12-10, 02:14 PM
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Carrier junk

if he had no negative pressure,and as sp said the hole is clear inot the furnace...then your vent pipe is blocked ,partially blocked,or something wrong with the venting part of the system
 
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