Suburban furnace does nothing

[chevyman07]

I have a 2018 Heartland Big Coutnry 3850MB that the Suburban Furnace doesn't work. I'm thinking it's a power problem because it won't turn on at all. My only problem is, where do I start checking for power? It worked great last winter and it hasn't tried to this one. Luckily I'm only in Central Texas and it hasn't been that cold. Any help would be appreciated.

 

[AbdRahim]

You may want to search YouTube. I think there is a tech whose channel is My RV Works, that has a number of videos on furnace troubleshooting.

 

[chevyman07]

You may want to search YouTube. I think there is a tech whose channel is My RV Works, that has a number of videos on furnace troubleshooting.

I will look for it in the morning. thanks

 

[TheLooks]

There is a switch on a Suburban furnace that must be reset. It trips for a reason. This switch is not obvious depending on the type of install. If you have a hatch that the intake and exhaust are in, then you can remove it and the switch should be visible. If not, you will have to get at it from the back and find the switch by feel or maybe even see it? The board will lock out after 3 tries to light requiring a reset. There are several reasons for the furnace not to fire. From low voltage, low gas pressure, dirt(hair) in the sail switch, or a faulty high temp limit switch. Even debris like bugs or spider webs in the gas tube or mud daubers in the combustion chamber. There may also be a fuse on the board. Good luck and I hope you have a hatch for access.

 

[chevyman07]

not referring to my on/off switch on the front of the furnace I'm assuming. I do have a hatch and can almost pull the unit out without undoing the wires. I will check for the switch on the back. Fuses tested good.

 

[TheLooks]

Yes, that is the one. Don't look further.

 

[TheLooks]

You should hear it sparking when it is trying to light. If not, then it could be a bad igniter on the board. If you hear it and can't see the spark inside the chamber, it might be bad insulation on the wire and it is sparking somewhere it shouldn't. When first started it will run for about 15 seconds and then try to ignite(sparking) You will smell gas at this point. Then it will purge for 15 seconds and try again. It will do this 3 times and go into lockout. IF you determine no spark, pull the plug wire off the board and hold it with THICK rubber gloves and put the end close to the igniter connection and see if a spark jumps to the wire. If not, new board. If it does, pull the igniter assembly out and check that it is spaced 1/8 inch from the ground shaft.
If you have good spark, you should be able to hear the gas valve open and close as well. This is a distinct thunk. IF you have been smelling propane, probably it is fine. If you can ohm out the coils on the valve they should be about 40 ohms.

 

[chevyman07]

so does the power come directly from the inside thermostat to have power at the wires going down to the furnace? my switch has been on since the beginning. I did clean out a dirt dobbers nest in the blower motor housing.
I just can't get power to my wires by the furnace, not too real sure about where it comes from.

 

[TheLooks]

Power goes to the furnace from the fuse panel, then it feeds to the thermostat and back down on blue wires.

 

[TheLooks]

Check for a fuse on the back of the thermostat. Check for 12v on one of the blue wires. If you switch it on and it does not apply 12v to the other blue wire it is the tstat. There is a schematic in the outer housing. Check that for the 12v path.

 

[chevyman07]

So I have no power to the blue wires, I even cut the factory wire caps to check just the blue wires coming down. Fuse ohmed out good, so it's possibly the crappy Dometic Thermostat they put in this rv. I've replaced it twice upstairs already and once down stairs

 

[TheLooks]

Did you check the dedicated 12v fuse in the fuse box for the furnace?

 

[chevyman07]

Yes. mine is a 15amp fuse. I pulled it out, made sure it wasn't burned and ohmed it. should I pull the fuse out and test where it is for power?

 

[TheLooks]

You can, it would prove it is there.

 

[TheLooks]

Send me the model # of the Suburban. Take a pic if you can.

 

[chevyman07]

I will tomorrow. no power coming out of where the fuse should be at

 

[gibsito]

I will tomorrow. no power coming out of where the fuse should be at

Did you ever get it going? If you want to check the thermostat you can bypass it by removing the two blue wires and twisting them together. That's all the thermostat does, makes a connection between those two wires. That tells the heater to turn on. This video is of an old Suburban heater repair, but probably the same principle as the new ones:

 

[chevyman07]

Have not yet. I even replaced the thermostat. at first the ac would run on either ac or furnace, now it won't run on ac. so I think im going to return it.
will try to twist the wires together tomorrow. if it don't work, going to try to find someone to take a look at it.