Last winter featured only a few weeks of the furnace working but laid the foundation to the opportunity to finally learn all about furnaces. It started in December when we noticed that the furnace had quit working. I began my troubleshooting by observing the behavior. What I found was that if I shut the furnace off and then turned it on it would cycle through running a small fan in the exhaust then turn on the igniter followed by the gas turning on, the furnace lighting and then running for about a minute and a half. It would then shut off, the cycle would repeat the same as before but this time it seemed to only run for 45 seconds. After that it would shut down and not restart until the power was cycled to the furnace. Did a little internet research and determined that it must be a bad flame sensor.
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| Note Flame Sensor circled in red |
Some internet experts seemed to think that they could be cleaned, I tried that with no change. I found a source locally for a new one and bought it for about $30 and installed. No change. Drat. Some more internet research led me to take a look at the air filter which had not been changed in a long time. It was completely blocked. Oops, that was dumb. Replaced filter and of course the furnace ran fine. Oh well at least I have a new flame sensor.
That lasted for about three weeks before it quit again. By now we were in the middle of January and it was getting really cold. The "TV room" which was once upon a time the garage before being made into a room has baseboard electric heat. I cranked the temp in that room up to 78 and left the door open to the rest of the house. That seemed to keep things above freezing.
The new symptom was different. The exhaust fan would run, no sign of life from the igniter but after a while I would hear the gas turn on for about 15 seconds before shutting down. As before the furnace would cycle through this two times before shutting down for good. Back to the internet maybe the igniter is bad. Did see some things to look for. Didn't really see any signs of cracks in the old one but I was desperate so I bought a new one and put that in. I can't say that I was surprised when it didn't make any difference. Oh well at least I have a new one to go along with my new flame sensor.
This began what became hours of troubleshooting. By now I had determined that my Amana furnace was from about 1997. I found a factory service manual online. After studying the manual and some troubleshooting I determined that the three leading candidates for the problem were:
- Problem with the the draft sensor
- Control module
- Wiring problem
I started with the draft sensor. I didn't have a manometer to test the draft in the exhaust created by the small fan but I tried cleaning the pilot tube that had a rubber line connected to the sensor. I checked wiring, I measured lots of voltages but still wasn't sure what was going on. Turns out that the furnace control logic is pretty simple but this furnace has had I believe 2 air conditioners installed, at least one humidifier and showed signs of a number of repairs. Lots of wires, no idea what any of them did. Eventually I found a replacement control module on Amazon.com that I bought for $100. By now we were getting sub zero cold forecast and I was desperate. I figured that the probability of this fixing it was about 10% at best. By this time I had also found a way to get the furnace to run for one cycle! All I had to do was recycle the power, wait until I heard the gas valve open and light it with a match! Not recommended from a safety standpoint and certainly not real convenient but if I set the thermostat on 85 it would run for a long time and get the house quite hot before the inevitable occurred and it would shut off without being able to restart again. This was enough to keep the pipes from freezing through the worst of winter and by March with temps going up I stuck the new uninstalled control module in a drawer and focused on moving from the estate executor trying to keep the house from self destructing to a homeowner trying to fix the place up.
By now it is mid November and it is starting to get cold. Also we are working more indoors than we were during the warmer weather. A furnace would be a good thing. Ray was home in mid November for his birthday. We looked at it briefly and determined that it was worth it to install the control module. I didn't want to start until we had the service manual with us and had studied it. So we went home and studied the manual, The wiring didn't look that bad. Ray had to go back to Nashville the next day but he came back for the week of Thanksgiving. Again we looked at the furnace and noted that there was some sort of large box labeled Elect-Tron directly in front of the control module. Looked like it would have to come out.
Did a little bit more troubleshooting and found that by now the furnace was 100% dead. No exhaust fan, no blower, nothing. Spent some time checking the thermostat, it appeared good as far as I could tell. Took apart the switch to the furnace and measured the incoming voltage. Nothing. Checked the circuit breakers, only one that was off was the one intentionally off to the barn. Turned it on, still nothing. Great, I am thinking somehow we have managed to screw up the electrical wiring in the house. I started following the wiring into the furnace and find an ancient box, On the side it has a handle to open or close the circuit. Opened the box, exposed contacts for the switch and a blown fuse. Of course this is the old screw in fuse that nobody uses anymore. Turned out they still sell a few at Home Depot, bought the fuse and replaced. Turned the furnace on and we are back to the original problems. By now it is too late to tear into the furnace.
The next day while I was at work Ray and Gloria went over and Ray started trying to figure out how we were supposed to remove the Elect-Tron. Eventually he removed the cover to it and look what he found:
By now it is mid November and it is starting to get cold. Also we are working more indoors than we were during the warmer weather. A furnace would be a good thing. Ray was home in mid November for his birthday. We looked at it briefly and determined that it was worth it to install the control module. I didn't want to start until we had the service manual with us and had studied it. So we went home and studied the manual, The wiring didn't look that bad. Ray had to go back to Nashville the next day but he came back for the week of Thanksgiving. Again we looked at the furnace and noted that there was some sort of large box labeled Elect-Tron directly in front of the control module. Looked like it would have to come out.
Did a little bit more troubleshooting and found that by now the furnace was 100% dead. No exhaust fan, no blower, nothing. Spent some time checking the thermostat, it appeared good as far as I could tell. Took apart the switch to the furnace and measured the incoming voltage. Nothing. Checked the circuit breakers, only one that was off was the one intentionally off to the barn. Turned it on, still nothing. Great, I am thinking somehow we have managed to screw up the electrical wiring in the house. I started following the wiring into the furnace and find an ancient box, On the side it has a handle to open or close the circuit. Opened the box, exposed contacts for the switch and a blown fuse. Of course this is the old screw in fuse that nobody uses anymore. Turned out they still sell a few at Home Depot, bought the fuse and replaced. Turned the furnace on and we are back to the original problems. By now it is too late to tear into the furnace.
The next day while I was at work Ray and Gloria went over and Ray started trying to figure out how we were supposed to remove the Elect-Tron. Eventually he removed the cover to it and look what he found:
All sorts of burned wiring, some of which has managed to coat much of the inside with smoke. I guess this explains what finally caused the 75 year old fuse to blow. By now I was on my way home from work and quickly diverted over to the see it first hand. We took inventory of what wires needed to be replaced, the general gauge as well as the colors. Back to Home Depot, buy some wire and supplies and head back. Ray had a wiring diagram from the service manual that he had edited to show the colors of all of the factory wires. We studied this mess and decided to determine what every wire in the furnace actually went to. This process revealed a lot of wiring that went nowhere. In many cases this was wiring for perhaps an old Thermostat or a long departed air conditioner. Rather than remove this wiring apparently the the furnace techs just clipped them if necessary and left them in place. After pulling these all out at least the mess was a bit cleaner. By now it was too late to fix the wiring especially since that would have required a trip home to get the soldering equipment.
The next day while I was at work Ray and Gloria took the Elect-Tron fully apart, Replaced the control module and reinstalled the Elect-Tron complete with repaired wiring. I got off work and caught up with them just as they were wrapping up. Just in time for the moment of truth. Flipped the switch to turn the furnace on and.... drum roll please .....
No change. Then Ray asked did you ever reconnect the vacuum line? Nope. Hooked that up and tried again. Exhaust fan comes on, a seeming eternity with nothing else and then what do I see but the igniter is starting to glow, It gets bright red, the gas valve opens and with a satisfying whoosh the flames ignite into a series of pretty blue flames!
We finally have a working furnace. It may be almost 20 years old, it may not be a high efficiency model but it once again works. Not only that but we now thoroughly understand the control circuits and know where every wire goes. I would also go as far as to say that I believe that our workmanship was done to a much higher standard than at least some of the techs that have touched this furnace over the years.
Furnace all buttoned up, note the blue flames
