Community Forums

herbc · 11-24-2016, 05:14 PM

Thank you so much for that info. My unit does nothing and there is 12 vdc across the sail switch. That is because the fan is not running. Tomorrow I will remove the unit and jump the thermostat wires since that is the only thing I can think of that will prevent the fan from running except for a bad fan motor. I truly am just feeling my way around in hopes of saving some dollars. Will report results afterwards.

Herb

ScottyBye · 11-24-2016, 06:12 PM

Herbc... before I removed the furnace I would clean the contacts on the circuit board. Just in case. Easy was is to use a pencil eraser. The board can also cause the fan motor not to run. Removing the face plate on the tstat will give you access to the wires and screws. Give the all a tweak. Just in case any are loose or have bad connections. Can remember for sure but I believe jumpering between R to W will start the heat cycle.

herbc · 11-26-2016, 01:47 PM

Even after reading up on the theory this simple thing is driving me crazy. First it works and then it doesn't. Theory says when the thermostat calls voltage is fed to the circuit board which energizes a time delay relay which then starts the fan. Well, sometimes my does and sometimes it doesn't. Voltage always reaches the board but the motor does not always start. Sail switch and limit switch have nothing to do with this phase. Although my sail switch is staying closed when it shouldn't be I still believe the PC board is bad.

ScottyBye · 11-26-2016, 01:59 PM

the sail switch should only close when the air from the motor pulls it closed. Yes it is possible that the CB is faulty, but in my experience when this happens the LED will indicate this failure. I would suggest further troubleshooting the replay. Maybe it has bad contacts. Check to make sure you have voltage to the coil of the relay when the Tstat calls for heat and the CB energizes the TD relay. If it has voltage then the NO contacts should close thus energizing the fan circuit. The fact that it works SOMETIMES says that the Fan Motor itself is OK 99%

herbc · 11-27-2016, 04:41 AM

Thanks, Scott. The only relay I see(I think) is the one hard soldered to the PC board. I have jumped the Tstat to ensure intermittent contacts - no help. I have removed the wire from the sail switch to ensure the contacts are open to start with - no help. I have even measured for closed contacts on the limit switch and have also jumped those contacts to eliminate any intermittent problem there. There is power going into the PC board and from what I can tell that alone should start the fan motor(and it is good) unless whatever controls it on the PC is bad, When the thing does start the fan motor runs well but the fire does come on and off. That on and off is caused by intermittent voltage to the gas valve. I thought I was a fairly decent technician but I have since changed my mind.

ScottyBye · 11-27-2016, 08:58 AM

Well now...it may be time to get the part # from the CB and start shopping. Thinking that the intermittent loss of power may be why the CB is no showing a fault code.

Just one question.... where have you jumpered the tstat. At the terminal block of tstat? Or at the furnace? Just want to rule out the wires going from tstat to heater!

hoosierrun · 11-27-2016, 09:49 AM

Make sure your sail switch is functioning properly. It must be in the open position prior to the thermostat requesting turn on. If it is stuck in the closed position, the blower will never start because the control board logic locks out any commands.

What I just described is exactly what happened to me on a Suburban furnace (also a 2016 brand new model). Sometimes it would work and other times not. I ultimately traced it to a sail switch that was hanging up on the edge of the heat chamber and not falling back to the open position.

This may not be your problem, but worth checking out.

My story is at the link below. Granted, your furnace is a different brand, but I believe most of these are similar in design.

http://www.irv2.com/forums/f54/subur...ml#post3342210

herbc · 11-28-2016, 04:21 AM

So much good info and I appreciate it. Time has come for a new board. Power is at the PC board but does not come off the PC board to the fan. I will let all know how that turns out but am almost 95% positive it is the board. But I have been fooled before.

Herb

herbc · 12-02-2016, 04:36 AM

My unit is working. What a pain this has been. Installed new board and it did not work. I also had a bad thermostat which I felt was strange. Haven't gotten a new thermostat yet but I am sure that will finally fix the problem. Too bad items was unusual and it got me. Thanks to all who posted to help me out. It helped a lot.

Herb

ScottyBye · 12-02-2016, 08:07 AM

Herbc... glad to hear that it's now working but also troubled that it was the tstat. In an earlier post you stated that you had jumpered the tstat thus isolating that from the control circuit and the furnace still didn't work.

herbc · 12-03-2016, 05:05 AM

I did do that but with a bad PC board. I cannot say if both were bad when I started but it took the replacement of both to do the job. The thermostat contacts I measured when I last removed it made intermittent contacts, But I did jumper the wires at the T'stat. As I said, it was driving me crazy for such a fairly simple piece of equipment, But, then again, I am not the best technician around. Just glad it is working.

herbc · 12-15-2016, 06:13 PM

Installed new control board and new t'stat and it has worked fine for a week. Problem is it just stopped working again today. Here we go again. I am not sure but I believe the new board went bad. I will double check my theory but I still think the motor should run if voltage is fed from the t'stat.

ScottyBye · 12-15-2016, 06:51 PM

Geez.... that sucks.
Keep us posted.

herbc · 12-16-2016, 05:22 AM

Well, it was not the control board. Apparently during the travels the sail switch got out of adjustment. And I was wrong in saying the sail switch did not matter in starting the fan motor. It has to be open. Anyway, adjusted the sail switch and it is working again. Of course, this had to happen on the coldest day of the year(19 degrees here in Virginia Beach).