RUDD UGPH-10EBRJB Pressure switch questions

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Old 10-29-11, 02:51 PM
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Question RUDD UGPH-10EBRJB Pressure switch questions

My furnace doesn't fire up. It is a RUDD UGPH-10EBRJB


If I tap on what I think is the pressure switch, it starts working.

I pulled the 2 wires off of the switch and did a continuity test on it. when I sucked on the tube I got continuity.

I put it all back & it works for a few days & then stops.

I tap the pressure switch & it starts up. I bought a new switch & put it in. That one doesn't work at all.

As a test I pulled the 2 leads off of the pressure switch & connected them together. I thought this would remove the switch from the circuit. The furnace did not start up.

2 questions:

1) Do I have to have the exact same make & model switch when I buy a new one? I found one that appeared to be for my furnance (cost about $90). It looks different but has the same connectors & a single tube.

2) What is wrong with my logic on the test where I tried to take the switch out of the circuit?

Thanks for listening!! John B
 
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Old 10-29-11, 03:09 PM
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Since we just went thru a discussion on pressure switches, I'll let Seattle Pioneer try to answer the part about having the exact switch.
He's more familiar with specific ones than I.

The reason you can't just bypass the pressure switch is the control must first sense the switch being open then closed before it will allow the ignition sequence to go forward. This is a safety feature designed to prevent exactly what you did.
 
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Old 10-29-11, 05:17 PM
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Smile Thanks Grady

Thanks for the rapid response. that restores my faith in my logic. Also, per your polite notice that there was a previous discussion on this, i found some & did more reading.

The replacement that I bought had a setpoint of .8 & my original had a .3 so I have now ordered another one, this time with the correct setpoint.

I had a pro look at this last year. He tapped the pressure switch & it started running. He told me that my exhaust blower motor was failing and that it needed to be replaced (at $790).

I really appreciate the answer.

John B
 
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Old 10-29-11, 05:36 PM
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Exhaust blowers generally either work or they don't. I find it difficult to believe yours is "getting weak". Usually the problem is either up or downstream of the blower. Testing with a sensitive pressure measuring device is needed to truely diagnose the problem.
 
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Old 10-29-11, 06:59 PM
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Ummm. Your pro wasn't very professional if he tapped on the pressure switch, got the furnace going and left. You probably know that now.

Neither is replacing the pressure switch a good idea. About 2% of the time the problem is the pressure switch. So 98% of the time you spend the time and money to replace the pressure switch and your time and money is wasted.

Putting a different pre4sswure switch in is inviting a hazardous condition to get worse. The pressure switch is probably shutting off because some part of your heat exchanger, venting system or drain system needs repair. If you effectively bypass the pressure switch by putting the wrong one on, you can easily create a hazardous condition and/or create a much bigger repair bill when things gets worse, as they no doubt will.

It's possible that you might identify the defect that is plugging up your system, but often such problems are subtle and hard to identify. You can give it a try if you wish --- and I'd recommend putting in the original pressure switch again.

If you can't identify and correct the problem, you need to find a GOOD repairman to help you. A poor repairman doesn't have a manometer to read the pressure being applied to your pressure switch --- he may not know what a manometer is. You don't want to hire that guy.

A mediocre repairman has a manometer and can show it to you. It comes packaged in a nice new case and has obviously either not been used or used very infrequently. You don't want to hire that guy either.

A GOOD repairman can show you his manometer and it will have various lengths of rubber tubing and fittings attached to it. This repairman knows how to connect up the manometer to your furnace and read the pressure being applied to the pressure switch.

This is the repairman you want to hire.

How'm I doing, Grady?
 
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Old 10-29-11, 08:04 PM
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Thanks Guys - All excellent advice

Thanks SeattleP

I put the original switch back in last year when the new one did not work at all (I had the wrong one).

It works fine & then after 4 or 5 days it 'sticks' again. A little tap & it is back up & running.

My pro wanted me to replace the blower assembly for almost $800.
$800 is what I paid for the furnace 10 years ago (before install).

I'm going to call the guy that helped me out this summer. When my AC died, he told me to check the outside fuses before he came to my house. He saved me a service call. I think he might be a guy that would have a well worn meter & know how to use it.

THANKS A LOT
 
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Old 10-30-11, 05:22 PM
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SeattlePioneer,
As usual you did an excellent job in explaining the "professional" levels out there. Thank You for your help. I can do the work & explain to a customer as I go but not having the gas experience you do reciting a "how to" online gives me some difficulty. My years in the trade have probably been 98% or greater on oil burners & A/C. Again, Great Job & Thanks.
 
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Old 10-30-11, 05:57 PM
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No problem Grady --- my experience is all with gas and zero with oil --- so we make a valuable pair around here!
 
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