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Open Roads Forum  >  Class A Motorhomes

 > Suburban SF-42 furnace fixed-----------finally!

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427435

Rochester, Mn

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Joined: 11/12/2005

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Posted: 11/15/10 03:30pm Link  |  Print  |  Notify Moderator

After a month of tests, ordering parts, installing them when they arrived, and then more testing because the furnace still didn't work, it is now fixed.

Short Version:

One of the coils on the LP valve would short out after a few minutes of operation and shut the LP off.

Long Version:

I figured the high temp limit switch was bad or the fan motor wasn't putting out enough air volume. I replaced the switch and no change.

The motor was a little noisy, so I checked that. The commutator was worn but the shop I took it to couldn't/wouldn't fix it------they said the brush springs were also weak, and they couldn't find replacements. So I bought a new motor. That didn't fix it either. At least the motor is now quiet.

Called Suburban and they suggested checking the voltage at the gas valve. It started out at 12 volts but would drop to zero when the fire went out. Something was evidently, they said, telling the circuit board to shut off the gas valve or the board was bad. I jumpered the high temp switch and the sail switch and checked for voltage again. Again, the voltage dropped to zero when the fire went out. So I ordered a new circuit board. That didn't fix it either.

The only other thing that might be telling the circuit board to cut off the gas valve is the flame sensor/ignitor. So I ordered a new flame sensor/ignitor. That didn't fix it either.

Then I went back to the gas valve solenoids and spliced in a separate feed cable that I hooked up to a 2 amp battery charger. I hooked the charger up to it once the fire was started and monitored the voltage again. The fire went out and the voltage dropped from 12 volts to 7-8 volts-----so the coil must be shorting out. With just the minimal current from the circuit board, the voltage would drop to zero, but the extra current from the battery charger was enough to show that it wasn't the board cutting if off.

New gas valve and it now works.


If anyone needs a good used circuit board or ignitor/flame sensor, PM me.


Mark

2000 Itasca Suncruiser 35U on a Ford chassis, 80,000 miles
2003 Ford Explorer toad with Ready Brake supplemental brakes,
Ready Brute tow bar, and Demco base plate.


SRT

Head of the Lakes, MN

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Posted: 11/15/10 04:00pm Link  |  Print  |  Notify Moderator

Congratulations! You're now experienced in troubleshooting/fixing Suburban furnaces


SRT
2000 32' HR Vacationer with Banks
1998 Subaru Outback Ltd. 5 spd
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Sully2

Cincinnati

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Posted: 11/15/10 04:10pm Link  |  Print  |  Notify Moderator

Do you make house calls if mine goes haywire?....LOL


2000 Country Coach Allure; Cummins ISC 330 HP; 71/2 - 8 MPG regardless
2002 Jeep Liberty


Hank MI

Brighton, Michigan

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Posted: 11/15/10 04:12pm Link  |  Print  |  Notify Moderator

SRT wrote:

Congratulations! You're now experienced in troubleshooting/fixing Suburban furnaces


You should open a repair shop. When mine starts acting up I'll come see you.

Glad you found the problem. I thought the gas valve was bad on my home furnace. We came home from up north in the winter and the house was like ice. Turned out it was the control board. Being a weekend and winter I had to call for service, that was an expensive repair bill.

Daveinet

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Posted: 11/15/10 04:23pm Link  |  Print  |  Notify Moderator

Intermittent electrical is the worst.

So what is your fastest time of pulling the furnace and reinstalling it? You have to be pretty good at it by now.


Dave

The Flying Fortress
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427435

Rochester, Mn

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Posted: 11/15/10 04:45pm Link  |  Print  |  Notify Moderator

Daveinet wrote:

Intermittent electrical is the worst.

So what is your fastest time of pulling the furnace and reinstalling it? You have to be pretty good at it by now.



As you know, determining which tools are needed is half the battle. I'm now at the place where I could grab a cordless drill with a Phillips bit, a 15/16" and a 7/8" open end wrench and have it out 2-3 minutes. I can also pretty well strip the furnace down (necessary to replace the fan motor or the gas valve) in less than 10 minutes.

* This post was edited 11/15/10 06:45pm by 427435 *

427435

Rochester, Mn

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Posted: 11/15/10 04:47pm Link  |  Print  |  Notify Moderator

Hank MI wrote:


You should open a repair shop. When mine starts acting up I'll come see you.



It'll only cost you parts and a 12 pack of Grain Belt.

fcooper

Richmond Hill, Georgia

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Posted: 11/15/10 07:27pm Link  |  Print  |  Notify Moderator

Wow. Impressive troubleshooting and repair.
Thanks for the informative post.
Fred


Fred & Vicki
Richmond Hill, Ga
2000 Holiday Rambler Endeavor/Freightliner/330 Cat
2000 Honda Odyssey toad w SMI Silent Partner braking system
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Hank MI

Brighton, Michigan

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Posted: 11/15/10 07:34pm Link  |  Print  |  Notify Moderator

427435 wrote:

Hank MI wrote:


You should open a repair shop. When mine starts acting up I'll come see you.



It'll only cost you parts and a 12 pack of Grain Belt.


That's one heck of a deal! Your on, I'm saving this post so no backing out later.

deandec

Northern CA

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Posted: 11/16/10 10:27am Link  |  Print  |  Notify Moderator

Hmmm....do they still make Grain Belt Beer?


Dean
95 CC Magna, Jeep GC


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