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Old 03-11-2009, 04:44 PM   #1
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Can Someone confirm my furnace diagnosis?


Hello Everyone, I was hoping someone could help me out , and verify my diagnosis to my furnace issue.

I have a Rheem RGDG-07EAUER furnace.

Two things are happening. The first issue is that the furnace shuts down before the desired temperature is reached. This happens intermittently. The furnace runs fine for a day, then cuts out the next during the morning Call for Heat. I've tried two thermostats, but I have yet to verify that the board is receiving the 24v at the time it cuts out.

The more persistent problem is that during the initial ignition sequence, the draft fan starts up fine, the ignitor glows, and then the gas valve opens and closes in a fraction of a second. I have verified that the 24v is sent to the valve for only this split second. I do not believe it is a flame sensor issue, as the time it takes to open and close is shorter than the time it takes to normally ignite, so if it was a flame sensor issue, i'd think it would be not working all time, instead of intermittently. I have verified that the valve is recieving the constant 24V when it is working correctly.

From what I can tell this problem just seems to be a faulty control board. Are miscellaneous issues like this a typical symptom?

I've replaced a board before in another furnace, but the place I purchase from allows no returns, so I'm a little hesitant to drop the $ before being sure that will fix the issue.

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Old 03-11-2009, 05:35 PM   #2
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Can Someone confirm my furnace diagnosis?


Quote:
Originally Posted by beckkl View Post
The first issue is that the furnace shuts down before the desired temperature is reached. This happens intermittently.

The more persistent problem is that during the initial ignition sequence, the draft fan starts up fine, the ignitor glows, and then the gas valve opens and closes in a fraction of a second.

From what I can tell this problem just seems to be a faulty control board.

Or faulty sensors telling the board to act like this.

Try a Google search for your symptoms, with make and model.

Are there any other symptoms that could indicate that your incoming power is flaky, or just that power to the furnace is flaky?

Your chances are better if you can find a way to reliably reproduce the symptoms.

Can you post a schematic of the furnace and/or control board?
I think for a weekend's worth of labor and a few bucks in parts you can make babysitting circuitry that will latch on the fault and considerably narrow your likely choices for the root cause.

The Bryant people sent me a free factory manual showing the normal sequence of operations for my furnace, and this manual has saved me a lot of money over the years. I have replaced an inducer motor, blower motor capacitor and an overtemp switch. I diagnosed a gas valve problem and had the tech confirm my diagnosis and replace the valve (I don't work on gas pipes).

A third party may sell DIY manuals for furnace repair; they certainly sell them for appliance repair.

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Last edited by Yoyizit; 03-11-2009 at 05:41 PM.
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Old 03-11-2009, 07:36 PM   #3
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Can Someone confirm my furnace diagnosis?


a meters a good tool.. across pressure switch,is board constantly getting 24v.may save some money if u know how to read it..
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Old 03-11-2009, 10:16 PM   #4
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Can Someone confirm my furnace diagnosis?


Yeah, I've been checking everything I can with my meter... My best guess at this point is something is throwing it into lockout. It seems to fix itself if I cut power to the furnace for a minute or so. Thanks for the ideas.....

The pressure switch is sending 24V all the way across...... BTW what the heck is that thing supposed to do?
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