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Ruud furnace won't light

I have a ruud deluxe 90 nat. gas unit built '87. The furnace turns on and the igniter glows, but won't light. The relay to the gas valve comes on about 15 to 20 sec. after igniter but I don't fell the gas valve open. I measured the voltage at valve and get .02V then 10.47 volts for a few sec then drops to .02V. ( From my vom meter I have to ground the red wire or I get a Neg. voltage reading. ??? )
I pulled the yellow wires off the circut board that come from the transformer and I don't get 24V or any voltage for that matter when 110v is on.
I don't think it's the valve because I can get it to open from the power of a 9V battery.
Is it a bad transformer or circut board problem or what?
Any ideas?

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Re: ruud furnace won't light

First lets try the transformer. With your meter check for 24v on the output side. You cant check to ground on this, you have to check your meter with both wires to the transformer. If this is too complicated just try turning on the A/C, if it comes on, the transformer is good. The problem may be with the time delay relay. try by-passing it and then see what happens. since its an '87 when you say circuit board I assume its a board with all the low voltage wires attached to it right? Or does it have resistors, diodes, and relays molded into it?

Posted on Nov 04, 2007

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