My furnace was working fine until an event. The event was that the thermostat got switched from heat to cool on an unusually warm Easter day. Problem was that I had a trap over the air conditioner to keep critters and debri out. I estimate the a/c was on for 10 minutes. When I saw the tarp blown up like balloon I went to take it off, bu the a/c unit shut off just at that time. Ever since - no heat. Here is what I have and what I have done so far - in order to the best of my recollection.

Furnace = Intercity Products - The General 90 - Mfg March 1992
Controller = White Rodgers 50a50 110 - No light lit or flashing at all
Thermostat = Maple Chase programmable
A/C unit = Split System AG Series

I first tried shutting the thermostat off for a few minutes - then swiching it to heat/auto and upping the temp. - Nothing at all.

I checked the fuse box - no breaker tripped.
I turned the main power switch to the furnace off for about 20 minutes and back on - nothing at all.
I checked the controller - no lights blinking at all. Put panel back on and power back to unit. Still nothing happening at all.
I reset the themostat - both by using the reset button and then removing batteries - nothing happens.
I tried flipping the breaker in the main electrical panel just for grins - flipped it back on after 5 minutes. Still no light on controller - no action at all.
Looked for a fuse of any kind anywhere in the furnace - could find none.
I then searched the web for 2 hours and read countless forums - lots of talented people - none with my condition.

My novice guess is either the controller is fried completley or there is a fuse I can't see or there is a wire that broke (like a fuse) when the AC unit over heated.

These are my questions - is there a secret reset fuse somewhere? Does this sound like a power issue? Does the AC unit have to be in working order for the furnace to get power? Could the AC potentially overheating have fried something in the furnace/controller? If this is a power source problem what is these easist way to check it? I am not a super handy guy - but I can follow steps if they are fairly clear and have some degree of detail.

The 50 a 50 should have a small 3 amp car type fuse on it. Does the fan work if you move the stat to fan on? The ac over heating should not have caused anything in the furnace to stop working.

Thanks for your reply. I can't find a fuse of any sort. Is it under a cover? Is it old style glass car type or new style small plastic? I just tried the Fan only mode and nothing happens.

I'll second that idea. The transformer or small fuse (usually a 3 A automotive style) is blown. The fuse is usually on the circuit board.

This might be a case of the transformer blew to protect the fuse.

The AC unit should have went off on high pressure and shoul ave not affected the furnace, Suspect coincidence.

For the NEXT WINTERIZATION:

The disconnect outside if it has a removeable tab, it can be turned upside down to put the AC permanently off. If compressor heaters exist, sometimes power should be applied for 24 hrs before AC is turned on.

Make sure you try to move all the breaker to the OFF position. There should not be any movement.

Should be the new style plastic 2 pronge fuse. Do you have the old wooden looking board or the newer white board. Should be pluged right to the board. Or it may be inline from the 24 volt power wire from the board to transformer. Will say 24 volt power, or xfmr

The board is white. I still do not see a fuse. The wires from the xfmr positions on the board (white and black) feed into a unit that has a solid black metal center and two plastic covers on each side. One side the xfmr wires connect in, the other side a blue and a yellow go out and back over to the top right of the controller board.

What about the fuse in the switch on the side of the furnace? Is the bottom door on the furnace good? If not the door switch may be keeping the unit from running.

I just checked the switch on the side of the furnace - no fuse, just an ordinary electrical switch. I also made sure the breaker in the main fuse box was all the way on as KISS suggested. Not sure what he means by transformer - is that the thing that the wires from the xmfr slots are going to? As far as the switch that activates when the bottom cover is on, I disconnected both wires, plugged a multi meter in and got nothing - (making sure the breaker was on, the thermostat was set to heat and blower to on and the switch on the side was on). Got no reading at all. -I tested the multi meter in a socket to make sure I had it set right and got the correct reading. Does this test make you think that maybe the thermostat is never sending a signal and that is why I have no blinking/solid light on the controller? If so, any tricks to testig the thermostat?

The 50a50 thing is a generic module from white rodgers. It's not the model of the furnace. The module is obsolete, but this is a replacement: http://www.emersonclimate.com/Docume.../0037-6590.pdf

If it uses the same designation, then between the termnals XFORMER and XFORMERN, there should be 24 VAC. Bet it isn't there.

LINE and LINE N should have 120 VAC on it. Make sure any door switches are closed.

If you have the 120 and not the 24 VAC then the transformer is BAD UNLESS there is some other safety in series with the XFORMER terminals.

DOn't know if there is a wiring diagram of the furnace online, but there should be one on the access door.

Many companies skimp on the fuse or don't use an energy limiting transformer. The generic wiring diagram doesn't show one.

Not having any display on the tstat means the 120 VAC is missing the 24 VAC voltage is missing. The 120 VAC must be present first, but it makes sense to measure the secondary first.

I was trying a few things before calling it a night. I was able to successfully test for voltage at the Hot and Neutral LINE in wires with the door switch activated. So I know the door switch is good and there is juice feeding into the controller. I am having trouble figuring out how to by-pass the thermostat or test it. (I'm not that good with the multi meter). Any guidance? Is there a way to feed the correct juice directly to the Red and white posts on the controller (like using a battery)? I'm thinking I want to be sure that it is not the thermostat before I start buying a transformer or controller. If I follow your logic KISS, (which I am not sure I am - I am a novice) then you are saying that if I test the voltage coming out of the controller at xformer terminals (prior to going into the transformer) - it should be 24 (or 120?) - if it is zero, then I have either a bad controller or no signal from the thermostat to the controller. If I have the voltage there, and not after the transformer, then the transformer is bad? BTW - thanks for sharing the proper winterizing with the power off at the outside breaker.

From what I am able to tell, you have the direction of signal wrong.

The LINE terminals on the controller are basically transformer in (120 VAC).

The Xfmr terminals are transformer OUT (24 VAC). Your looking for the voltage between XFMR and XFMR N. There is no need to disconnect terminals.

The transformer should be mounted externally. You don't need to remove wires to test.

You can, but don't get any wires mixed up measure the resistance of the primary (between the terminals connected to LINE) and the resistance of the transformer on the load side (between XFMR and XFMR N). Measure the resistance between the wires connected to the transformer at the transformer side.
You can do each separately. Expect to see infinate resistance between XFMR and XFMR N indicating a bad transformer.

Make sure you turn off power when disconnecting or doing resistance checks.

Incidentally, XFMR N is the (C) connection to the thermostat when used.

Take the t-stat off the wall and put a jumper from r to w, or do it at the control board. This will bypass the t-stat. and the heat should come on. r-w for heat r-g for fan, or r-y for cooling

Thanks for your help Joshdts and KISS - I thnk I got it. I read up some more on how the thermostat wiring works and found that if I just jumper the R and W at the controller board I take the thermostat out of the equation. Once I did that I checked the voltage coming out of the controller into the transformer, it was good. I checked the voltage coming out of the transformer, it was = 0. So I bought a new transformer and installed it. With the thermostat still disconnected and using the jumper from R to W, I can get the furnace to cycle through and ignite and blower too. All that is left is to reconnect the thermostat and make sure she works fully connected. Sure seems funny that the transformer would blow coincidently with the A/C incident, but who knows...

I hate when that happens, but it was what I suspected.

While your at it get a 3A automotive fuse and fuseholder and install in the Xformr terminal lead. It's a cheap insurance policy.

Is the LED light on the controller 50a50 to be on all the time?
In my furnace it goes on for 1 second and then goes off.. and nothing works.
Fuse and transformer are good.
Do I need a controller.