Baby its cold outside - and inside

[JanAndBill]

Furnace has been working fine till last night. Woke up to a cold trailer. I have an automatic regulator set to switch over. When I checked the tank it was drawing from was empty but the indicator window didn't show empty. I manually switched the valve to the full tank, but now the furnace won't come on. Nothing. Checked the fuses and all good. Is there a reset somewhere?

 

[jnbhobe]

Will the stove top lite??

 

[JanAndBill]

Stove and hot water heater works

 

[jnbhobe]

There may be a reset on the board, have you turned off all power to it including the thermostat then turned it back on, they will lockout after three tries. Also check the sail switch.

 

[dbbls59]

Could be air in the line. Try cycling it off and on a few times.

 

[danemayer]

After cycling the thermostat off and back on, the blower should start and after about 20 seconds the gas valve should open and there should be three ignition attempts.


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[JanAndBill]

After cycling the thermostat off and back on, the blower should start and after about 20 seconds the gas valve should open and there should be three ignition attempts.


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Tried cycling thermostat off then back on, also tried pulling the 20 amp fuse. Nothing no blower, no ignition, nothing. When you set the thermostat to furnace the indicator will display the temperature and you can raise and lower the temp.

Don't believe it's air in the lines, because the stove is downstream, and it lights and burns blue.

 

[danemayer]

Tried cycling thermostat off then back on, also tried pulling the 20 amp fuse. Nothing no blower, no ignition, nothing. When you set the thermostat to furnace the indicator will display the temperature and you can raise and lower the temp.

Don't believe it's air in the lines, because the stove is downstream, and it lights and burns blue.

No blower is probably 1) general 12v problem, 2) loose wire between thermostat and furnace control board, 3) bad control board.


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[JanAndBill]

No blower is probably 1) general 12v problem, 2) loose wire between thermostat and furnace control board, 3) bad control board.


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Leaning toward bad control board. Is there a trick to getting the door off, seems like the vent tubes are glued in with some strong caulk? Also, how can you tell which model number furnace you have???

Thermostat has been off for a 4 hours, tried turning it on and running the temperature up to 90. Nothing came on no clicks no nothing.

 

[JanAndBill]

Ok got the door off and can see the control board. Before I start disassembling more, had DW cycle the thermostat inside while I listened outside. When the thermostat is cycled, after a few seconds, there is a faint click, but nothing happens.

 

[danemayer]

You probably have a Suburban SF42 (42,000 BTU).

I've attached a wiring diagram. If you can get to the control board terminals, check voltage on the control board. On the right hand side of the control board diagram, there's a terminal where you should read 12V DC when the thermostat closes. The connection next to that should be powered as well in order to start the blower. If you aren't getting power to either, check the wire nuts.

It's worth checking connections at the thermostat end. Also, the Dometic Single Zone Digital Thermostat wiring goes to a relay box in the air conditioning. If you have a main air dump, it's just above the air return. Then from the relay box, 12V goes to the furnace.

 

[JanAndBill]

To dark to see well, going out tomorrow. The control board is mounted on a sheet metal arm.looks to be to tight to do much of anything with it in place

 

[travelin2]

Ok got the door off and can see the control board. Before I start disassembling more, had DW cycle the thermostat inside while I listened outside. When the thermostat is cycled, after a few seconds, there is a faint click, but nothing happens.

Same scenario that happened to us last May. Nothing happens in the coach but when cycling the thermostat a click outside at the furnace.
We had a mobile tech replace the circuit board because ours was still under the Suburban warranty.
Then there was heat!!
BTW-I'll do it myself if there is ever a next time.


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[JanAndBill]

Pulled the circuit board and on my way to get it checked, if not the dealer has a replacement. Hopefully this afternoon, it will be back in operation.

Quick question. When I start sealing everything back up door/vent/etc. do I just use a good white silicon caulk? Or do i need something that hardens or withstands high temp?

 

[travelin2]

Quick question. When I start sealing everything back up door/vent/etc. do I just use a good white silicon caulk? Or do i need something that hardens or withstands high temp?

Mine had none to start with, so there's none on it now.


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[JanAndBill]

When I talked to the service mgr at our dealership yesterday morning, (super guy by the way), he said he had the circuit boards but not the tester. Said he wouldn't have it till this afternoon. I assumed he was getting one from one of their other dealerships. When I walked in this afternoon, there was the service mgr, with a box of toys on his desk and grin on his face like a kid at Christmas. He said he had been asking for one these for awhile, and when I called he used the excuse that he needed to satisfy a good customer to order one overnight (before they could change their mind). Course he made sure to get all the attachments so that he could test a whole shopping list of things in a RV. LOL In a matter of a few mins he was able to verify the board was bad (fan relay). So with a new board in hand, we spent the next several minutes playing with his new toy, and testing everything we could find. If you're ever in need of service in Albertville, AL be sure to call on Bankston Motor Homes. Great bunch of people. Only problem is I wasted to much time to get the board back in today.

 

[JanAndBill]

AAAARRGGG. Back to the drawing board. Plugged in the new module, and nothing. I've got a constant 12 volts coming from one blue thermostat wire (which is supposed to be correct) and 12 volts to the other thermostat wire only when the thermostat is turned on. I hooked up a separate power source to the blower and it runs fine. If I pull the plug at the board, I have power through the blue thermostat wire when the thermostat is turned on. I don't have any power on the red wire (from the sail switch and limit switch) at the plug. This is the wire that comes from the sail switch and the limit switch which may mean one or the other could be causing the problem. I'm wondering if I power this with 12 volts, and the blower works, would that then mean I had narrowed it down? It appears these two switches are wired in series one to the other.

 

[danemayer]

When the thermostat closes, power should be applied to the blower. After the blower gets up to speed, the sail switch closes, and assuming the limit switch is closed, the board will power the gas valve and igniter. So the sail switch/limit switch circuit only comes into play after the blower starts.

Check the wire connections and look for wire nuts.

 

[JanAndBill]

I guess I don't follow you on this, because I have power everywhere I'm supposed to at the furnace except the blower terminal off the board.

 

[danemayer]

I guess I don't follow you on this, because I have power everywhere I'm supposed to at the furnace except the blower terminal off the board.

If you have 12V at the power terminal that's next to the blower terminal, and a good board, but the blower doesn't start running when the thermostat closes, it must be a wiring problem. But when the thermostat closes, you should see 12V to ground on the blower terminal. Keep in mind that after 3 ignition attempts, it goes into lockout mode and the blower is no longer powered.