This system is running the fan continuously and the surface igniter even with the thermostat off. It has three lights on the board and two of them are green and the flame light is yellow. Is this board fried? Is there anything else I can check?

 

Which fan is running? The blower that circulates air from the registers?, or the one that exhausts burned gas(inducer fan)? The fact it tries to ignite, even when you say stat is off, leads me to believe it is the exaust gas ventor fan. IF so, the stat may not be off, or you could have a short in a wire, or maybe the sequencer is stuck closed.

 

It the main blower running. It will only cut off on you take the lower cover off. I took the thermostat off completely and its still runs both. The inducer fan is not running.

 

Your scenario is an odd one. The blower could run due to different malfunctions. But to have the ignitor trying to come on, without the inducer motor running first, is strange to MOST furnaces.

Do you have a voltmeter to test to see if you have 24 volts between W and C, on your 24 volt terminal strip in the furnace, that your stat wires hook to down there?

Do you have 2 or 3 wire pressure switch? I'd also like to see if you have voltage at and through the pressure switch, with the stat off.

Does your control module have a legend somewhere, on it or elsewhere, that says what the lights mean?

Can you take a digital photo of your furnace's wiring schematic, and post it here? If you can, it must be clear.

 

The answers are below after your questions.

 

Since you posted this in the furnaces forum, rather than the a/c forum above, I presumed you had furnace issues.

With the stat turned off, do you have any power to any low volt terminal strip wire hookup in the furnace, besides R to C? Test every low volt wire to C and see if you get anythng - like from Y to C, and G to C......with the stat turned off.

 

Since the heater part was on I thought it might be better to but my questions here. I have 27 vots r to c and thats it.

 

With no 24 volt power continuing through the heating circuit, I really can't say for sure where you have that short, causing the HSI to try to come on (and the blower too), with the stat off or taken out.

A wiring diagram might make that more obvious as to what/where. Off hand, yes it would sound like some cross up on the board is allowing volts to get to the ignitor and blower. But I am not going to stick my neck out, while sitting here, saying the board is your problem for sure.

If I were you, I would look at that board real carefully with a bright light and possibly a magnifying glass, to see if you can see any signs of electrical arcing flash marks on the board.

 

ecman 51 I PMed you I have a diagram but I can't load to the forum for some reason I guess since I am new on the board.

 

OK I checked the board out and it looks OK on the front and the back. I disconnected the two wiring harnesses that go to the top part the gas valve,fan and igniter. and it still run thermostat off. I looked at all of the wires real good and I don't see no shorts. And thanks for the replies.

 

Heres the diagram maybe.

 

You have 4 resettable limit switches(see lower left of left side of drawing): 3 rollout switches and a vent safety switch. Each of these switches likely has a little pin located in the middle of the device between the two terminals/wires on each switch. Push them all in and feel if any make a little click. If they are NOT tripped, they will not click. If they click, then it tripped, and this triggered the blower to come on. The fact the HSI also comes on may or may not be some quirk in design with your furnace if one of these limits trips.

The roll out safety switches are out in front of each burner tube. The vent saftety switch is a spill switch located on the inducer fan housing.

No 24 volt current will be able to pass through this saftey circuit if the inducer motor is not running (probably). And it will not run if any of these resettable switches tripped(only the blower motor), so you must make sure none have tripped, and that each has continuity at each of their 2 terminals. Do this first and get back to me.

(I was not on the puter yesterday - sorry.)

 

If I'm looking at this right these limit switches are on the pc board itself. Only three of them looked like it might have a button but none of them would move.

 

No, they are not on pc board. They should be right on the devices themselves where I described the location of each of the switches to be. If you send a photo of your furnace inside the large furnace cover, I can show you.

 

OK here's some pics there is only one switch with a button and it was not tripped. The only thing on or around the burners is the thermal coupler. I disconnected the two wiring harnesses that go to all of this part of the unit and it still will run.

 

Just want to point out that the Ruud UGDG-07EAUER unit i worked on has a slightly different schematic. The flame sensor isnt present in the unit i worked on and i had to add a new one. Here is the schematic and a youtube video on how i replaced the control board, and add a new flame sensor.
RUUD furnace fan not starting - replace burnt control board - adding new flame sensor - no heat HVAC - YouTube

 

Hello, I'm Joe. Just thought I'd leave an addendum to this thread for anyone who stumbles upon it. On this Rudd unit, if any of the limit switches are open, I can attest that the main blower will run continuously. How do I know?

I purchased and renovated an old office building here that was once condemned (hurricane damage) and where getting gas reconnect is next to impossible. I live in Houston, Texas, the land of endless summer where a heater is seldom if ever needed. So up until this week space heaters have been sufficient. This week, however, has been colder than a witch's tit!

The building has an old Rudd Silhouette 2 gas furnace. I ripped out all the gas burners, and other gas-related stuff, pulled the wire plug from the electronic control board, cut a new metal plate to cover the opening, run new #6 wires to two 60 amp breakers, and mounted a universal 50,000 BTU electric heat coil. Added a new electronic thermostat and, Lo and Behold, the heater worked very well...

...EXCEPT FOR ONE THING! Alas, the blower would not shut off.

Unfortunately, I didn't take pics of the wiring before I ripped it out. Luckily I found this post with the schematic. Hot wired the board and it was good to go.

Just so you all know, before I did this I called several HVAC contractors to get a quote on how much they'd charge me to convert the gas furnace to electric. Two told me it was impossible; couldn't be done. The third guy said he could do it for $3,000. The heating element cost me $158. The rest of the materials about $50.

 

A nice idea firedawg, but I shudder to think what home insurance company would say if I did that and something went wrong. Not saying you aren't competent , but if wiring back to main panel can't handle it, someone is SOL and it won't be the insurance company. No quality company would touch it because they didn't want their name on it for insurance purposes. I wish you good luck with it.

 

It's been working great for three days. Still cold and nasty outside. Don't know what part of Texas you're in, but I'm ready for this crap to be gone and the 70 degree temps to roll back in!