pressure switch gas furnace

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  #1  
Old 10-28-08, 08:59 AM
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pressure switch gas furnace

How long can I run my ceiling mounted gas furnace with a jumper across the wires on the pressure switch? I can start the furnace with the leads to the switch taken off and once the inducer(?) motor starts I can jump them and the furnace runs correctly.
The furnace does not run with the wires attached to the switch. If there is some diaphragm inside the switch I'm sure it's blown out because prior to jumping the wires I blew it out with compressed air. That was probably the WRONG thing to do.
Right now it has been running as it should for about 25 minutes.
How long can i run it this way? From what I see I'll need to climb the ladder every time and unhook the jumper until the inducer stars, and then connect a jumper to get the furnace to fire up.
This is a ceiling mounted gas furnace in a drafty shop.
any idea of how much this sort of part should cost?
Thanks
Bob
102808 10:58
 

Last edited by BOBRESTORE; 10-28-08 at 11:31 AM. Reason: problem not described correctly.
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Old 10-28-08, 04:19 PM
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Look and see if you have a pressure switch where you can actually see the plunger suck in, and open the switch.
 
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Old 10-29-08, 07:41 AM
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It is assembled with rivets and doesn't apear to be serviceable.
I just started the heater this morning by turning off the power to the heater unhooking the jumper from the pressure switch and about 3 seconds after the small fan (inducer??) starts up I reattach the jumper and then I get heat.
How long can I operate the heater this way?
Thanks
 
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Old 10-29-08, 09:06 AM
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I wouldn't operate any furnace with a saftey by-passed. What if the switch is actually ok and there is another problem? Could be you are setting yourself up for a problem. If the vent is partially restricted you could be producing carbon monoxide. I'm not saying that is the case, but please be advised it could be.
 
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Old 10-29-08, 04:03 PM
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vent is clear, checked it today. should there be no gap when joining the smaller 3" pipe to the 6" pipe? Does there need to be a tight fit for there to be vacuum enough to activate the diaphragm switch?
I think I just answered the question. duh! I'll try making the transition from 3" to 6" more airtight tomorrow.
 
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Old 10-29-08, 04:16 PM
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A couple of ways you can check if the diaphram switch is working: One is to take a voltmeter and see if current that is coming into the one spade can flow out the other spade when it starts up. Easiest way to find out is to first disconnect both wires from it and find out which is the hot one (24 volts) coming in. Then once you identify that, then hook back up only that wire. Then test the bare spade of the other terminal when the furnace ventor fan runs to see if that spade yields 24 volts to ground.

The other way is to observe if the ignition process begins. If it does, then the pressure switch is fine and is activating. If it does not, then confirm with that voltmeter test and see if it gets 24 volts at each spade connection, as stated.
 

Last edited by ecman51; 10-29-08 at 04:26 PM. Reason: made a test easier
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