Suburban Furnace

[Jakeman]

I have a Suburban Furnace Model NT-34BW, that runs the fan, but won't light

I have been using the furnace over the winter while doing a floor and ceiling refurb with no issues.


I shut it down 3weeks ago and now when I call for heat the fan runs, but it won't produce any heat.


I am going to try and trouble shoot it this weekend.
Dose anyone know how to check the Module board?
Also I assume the sail switch (see pic) is for checking air circulation before the igniter will activate?

Thanks

[Domo]

Do you have propane?

[Old-Biscuit]

DC from FUSED source goes to Time Delay Relay (TDR) and to Thermostat
When thermostat closes calling for heat DC comes back from thermostat to the TDR energizing a coil which allows DC to fan motor

When motor comes up to 75% there should be sufficient airflow to Close the Sail Switch ---when closed DC goes to Circuit Board (RED wire 4 wire connector)
Circuit Board then sends DC to Gas Valve/Spark Electrode for Ignition

4 wire connector......
RED wire..DC+ from Sail Switch
Yellow wire....DC- Ground Terminal
Brown wire....DC+ to Gas Valve
Black wire.....Millamp flame signal from spark electrode

[Jakeman]

Originally Posted by Domo

Do you have propane?

Yes 1/2 tank, stove lights and generator starts.
Should have said that in post.

[Jakeman]

Originally Posted by Old-Biscuit

DC from FUSED source goes to Time Delay Relay (TDR) and to Thermostat
When thermostat closes calling for heat DC comes back from thermostat to the TDR energizing a coil which allows DC to fan motor

When motor comes up to 75% there should be sufficient airflow to Close the Sail Switch ---when closed DC goes to Circuit Board (RED wire 4 wire connector)
Circuit Board then sends DC to Gas Valve/Spark Electrode for Ignition

4 wire connector......
RED wire..DC+ from Sail Switch
Yellow wire....DC- Ground Terminal
Brown wire....DC+ to Gas Valve
Black wire.....Millamp flame signal from spark electrode

\




Thank you for the operation breakdown

[Petes Dad]

Bypass the sail switch by jumper in the wires together. A lot of times the fan bearings have excessive drag due to dirt, debris and wear causing it to not have enough speed and will not activate the sail switch

[veraken]

Here's a link to 2 files I just added to the FILES section which may help you. Let us know how you make out.

https://www.irv2.com/forums/download...do=file&id=428

https://www.irv2.com/forums/download...do=file&id=427

[Old-Biscuit]

Originally Posted by Petes Dad

Bypass the sail switch by jumper in the wires together. A lot of times the fan bearings have excessive drag due to dirt, debris and wear causing it to not have enough speed and will not activate the sail switch

More common issue is dirty sail switch, paddle binding

Jumpering the sail switch just provides DC to circuit board...motor/fan speed---airflow may not be sufficient for combustion

[Jakeman]

I checked the power through the limit and sail switch, have power to module.
I need to pull the unit to go further.
I'm thinking I might as well replace the board and igniter, as it's a pain to take out

[Domo]

Don't know what RV you have. We have two furnaces in our MH, which make troubleshooting (a little) easier as I can swap parts... just a thought.

[Old-Biscuit]

Originally Posted by Jakeman

I checked the power through the limit and sail switch, have power to module.
I need to pull the unit to go further.
I'm thinking I might as well replace the board and igniter, as it's a pain to take out

IF you have DC between RED and Yellow at circuit board but no DC on Brown (to gas valve) then circuit board is bad


OEM Board (521099)
https://suburbanrvparts.com/suburban...w-fan-control/

Dinosaur Electronics
*Better Quality boards
Might be able to use their UIB 64 or UIB S board
Call Tech Support..(541) 994-4344 M-F, 8:00 am - 5:00 pm PST

Spark Electrode (525029)
https://suburbanrvparts.com/suburban...-probe-525029/

[Jakeman]

I pulled the furnace and bench tested. (no propane hooked up)



When I give it 12v to thermostat wire it cycles on, after the delay the board signals the igniter to spark and sends 12v to gas valve coils, the signal only lasts 7 seconds, then goes away and never comes back, no mater how long I let it run?


I ohm tested the coils and they are both between 85.6 and 86.2


I'm assuming the board must be bad, the manual says it should make 3 attempts to light every 15 seconds, then go into lockout and shut down the furnace. It never makes the other 2 attempts or shuts down the furnace

[Jakeman]

Originally Posted by Domo

Don't know what RV you have. We have two furnaces in our MH, which make troubleshooting (a little) easier as I can swap parts... just a thought.

We just have the 1 furnace, it's and older 34' Winnebago diesel pusher.

[Jakeman]

https://manuals.heartlandowners.org/...11-05-2015.pdf