RV.Net Open Roads Forum: Need help with a SF 30 Suburban Furnace

RV Blog

  |  

RV Sales

  |  

Campgrounds

  |  

RV Parks

  |  

RV Club

  |  

RV Buyers Guide

  |  

Roadside Assistance

  |  

Extended Service Plan

  |  

RV Travel Assistance

  |  

RV Credit Card

  |  

RV Loans

Open Roads Forum Already a member? Login here.   If not, Register Today!  |  Help

Newest  |  Active  |  Popular  |  RVing FAQ Forum Rules  |  Forum Posting Help and Support  |  Contact  

Search:   Advanced Search

Search only in Tech Issues

Open Roads Forum  >  Tech Issues

 > Need help with a SF 30 Suburban Furnace

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 4  
Next
Sponsored By:
mikestock

Vestavia Hills, AL, USA

Senior Member

Joined: 12/01/2002

View Profile



Posted: 11/12/20 01:09pm Link  |  Quote  |  Print  |  Notify Moderator

My original problem was the usual story. The fan would come on and the furnace would fail to light and the fan would then shut down. I, standing outside could hear the switch and smell gas but the spark, I couldn't hear due to fan noise and it was failing to light the gas. I brought the furnace home and checked the over-temperature thermostat and sail switch. They were good. I hooked up a 12 volt battery and opened up the combustion chamber to check to see if I was getting a good spark, which I was.

Took it back and reinstalled it and the fan no longer came on when I called for gas heat. I could, however, use the external 12v battery to supply power through the green and yellow wires while jumping the two blue wires together. With the gas hooked up, the furnace came on and burned, just like it should. I had the internal thermostat out of the circuit and the only hook up to the rv was the gas source. I hooked internal wires back, just like they were originally but nothing would happen.

I'm guessing that I have a thermostat problem. I may have caused it when I back fed power by accident, blowing the 2 amp glass fuse in the thermostat.

Lacking any expert suggestions I guess I will go spend $80 for a replacement thermostat. This one is a 3 way, AC, heat pump or gas furnace. The ac and heat pump functions still work.

enblethen

Moses Lake, WA

Senior Member

Joined: 01/05/2005

View Profile






Posted: 11/12/20 01:18pm Link  |  Quote  |  Print  |  Notify Moderator

Locate the two wires feeding the furnace either at the thermostat or in the furnace. Connect them together. The furnace should start and then produce heat. If this happens, separate the two wires. The furnace should go into shut down mode and turn off.
If this happens, the problem is in the thermostat.
Make and model of thermostat? Number of wires in thermostat? Does it control the A/C?


Bud
USAF Retired
Pace Arrow

2003 Chev Ice Road Tracker


mikestock

Vestavia Hills, AL, USA

Senior Member

Joined: 12/01/2002

View Profile



Posted: 11/12/20 02:45pm Link  |  Quote  |  Print  |  Notify Moderator

enblethen wrote:

Locate the two wires feeding the furnace either at the thermostat or in the furnace. Connect them together. The furnace should start and then produce heat. If this happens, separate the two wires. The furnace should go into shut down mode and turn off.
If this happens, the problem is in the thermostat.
Make and model of thermostat? Number of wires in thermostat? Does it control the A/C?


Here on p.35 is the schematic of my unit. The wires coming down from the thermostat are bk, gn, y, wh and they connect to r, bl, bl, and y, in order, on the furnace.

I have no idea which pair of the bk, gn, y, wh to tie together. I see 6 possible pairs and don't know what further damage could be done by picking the wrong pair.

I do know that when powering the furnace with an external battery that the red and yellow wires power it up with the two blues tied together. Gas connected and the furnace lights and runs.

enblethen

Moses Lake, WA

Senior Member

Joined: 01/05/2005

View Profile






Posted: 11/12/20 03:43pm Link  |  Quote  |  Print  |  Notify Moderator

It is the two blue wires that come from the thermostat.
Red and yellow is the 12 volt DC supply.

mikestock

Vestavia Hills, AL, USA

Senior Member

Joined: 12/01/2002

View Profile



Posted: 11/12/20 04:53pm Link  |  Quote  |  Print  |  Notify Moderator

enblethen wrote:

It is the two blue wires that come from the thermostat.
Red and yellow is the 12 volt DC supply.


The wires from the thermostat are black, green, yellow and white.

The blue wires are both on the heater side. They are blue, blue, red and yellow.

Thermostat__________Heater
black------------------------red
green------------------------blue
yellow-----------------------blue
white------------------------yellow

Old-Biscuit

Verde Valley

Senior Member

Joined: 06/20/2009

View Profile



Posted: 11/12/20 04:55pm Link  |  Quote  |  Print  |  Notify Moderator

enblethen wrote:

It is the two blue wires that come from the thermostat.
Red and yellow is the 12 volt DC supply.


Red is 12VDC + (positive)
Yellow is 12VDC - (negative)

Red supplies 12VDC+ to the thermostat via the On/Off CB Switch (local/on furnace frame) (Blue) and DC Power to 'power' circuit on board

Thermostat closes and sends DC+ back to circuit board (Blue) and sail switch/limit switch circuit

Connecting the 2 Blues wires at thermostat makes up 'run' circuit...bypassing thermostat
If Furnace runs (Fan/Flame/Heat) then thermostat is problem

If furnace does NOT...check if the on/off CB switch is tripped///push button reset


Is it time for your medication or mine?


2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
On the Road Debt Free April '07
Off the road still Debt Free Jan. '14

mikestock

Vestavia Hills, AL, USA

Senior Member

Joined: 12/01/2002

View Profile



Posted: 11/12/20 05:17pm Link  |  Quote  |  Print  |  Notify Moderator

Old-Biscuit wrote:

If furnace does NOT...check if the on/off CB switch is tripped///push button reset


Are you saying this switch is a breaker? Mine is on.

I don't have two blue wires at the thermostat. I do have the two blue wires on the heater that make up when the over-heat thermostat is closed and sail switch closes. As I said originally, when the two blue wires from the heater are tied together and 12vdc are supplied by an external battery to the red (+12v) and yellow (-12v), hooked up the gas line and the heater started and ran. When I matched up the wires as they were, originally (see last post) matched, nothing happens.

The other 2 functions of the thermostat, ac and heat pump, work correctly.

I don't have a clue where the relay is located where the tiny wires from the thermostat transfer to the heavier wires to the furnace.

enblethen

Moses Lake, WA

Senior Member

Joined: 01/05/2005

View Profile






Posted: 11/12/20 05:23pm Link  |  Quote  |  Print  |  Notify Moderator

If the fan starts, the circuit breaker on the Fan housing is good.
On the terminal strip in the furnace is the best place to jumper the blue wires to bypass the thermostat. You can see what color wires from this terminal strip goes to the thermostat for the heat function.
Again, what is make and model of thermostat?

mikestock

Vestavia Hills, AL, USA

Senior Member

Joined: 12/01/2002

View Profile



Posted: 11/12/20 06:43pm Link  |  Quote  |  Print  |  Notify Moderator

There's no telling who made it. I have seen it with Coleman in the label. Here is a picture. My Phaeton has two just alike.

enblethen

Moses Lake, WA

Senior Member

Joined: 01/05/2005

View Profile






Posted: 11/12/20 07:23pm Link  |  Quote  |  Print  |  Notify Moderator

This should be the Manual for your thermostat.

Reply to Topic  |  Subscribe  |  Print Topic  |  Post New Topic  | 
Page of 4  
Next

Open Roads Forum  >  Tech Issues

 > Need help with a SF 30 Suburban Furnace
Search:   Advanced Search

Search only in Tech Issues


New posts No new posts
Closed, new posts Closed, no new posts
Moved, new posts Moved, no new posts

Adjust text size:




© 2020 CWI, Inc. © 2020 Good Sam Enterprises, LLC. All Rights Reserved.