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Randall
Randall, RVIA Certification
Category: RV
Satisfied Customers: 10334
Experience:  RVDA/RVIA Master Certified Technician with many years experience.
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I have a Suburban SF35 furnace that has problems. First,

Customer Question

I have a Suburban SF35 furnace that has problems. First, after reading the factory manual about how it's SUPPOSED to work,, I think that the control board has always had a problem. Here's the first part. I gather that the control board is supposed to try and light 3 times, then, if no heat, shut down. This furnace has never done this (I bought this 5th wheel used, and it didn't have the owner's manuals) Anyway, if I happen to run out of gas in the middle of the night it just keeps blowing until I shut it off. Most recently, it won't ignite at all. I have a hunch the control board--which has always had a problem--is totally gone now. I've gotten down and looked at the furnace, but like everyone else, I don't have a gas cutoff valve...so that means shutting the gas off at the tanks, and letting some amount of propane get into the trailer when I loosen the fitting...so I only want to do this one time. I guess my question is: what parts should I 'shotgun' in? Control board? igniter? gas orifice? I'd rather spend a bit more money and be done with it!
JA: Have you checked to make sure the thermostat is working? What about the coolant level?
Customer: Thermostat works fine. Coolant level? Huh? This is a furnace....
JA: What year is your Suburban?
Customer: 1999
JA: Are you fixing your Suburban yourself? What have you tried so far?
Customer: So far, it's been troubleshooting only. I've checked the limit switch with an ohm-meter, and the sail switch must be working because the fan keeps running...and running. That's it so far. Pulling the furnace out to work on it will be a monumental pain... so I don't want to do it more than once. I'd rather 'shotgun' parts than spend two weeks futzing around.
JA: Anything else you want the mechanic to know before I connect you?
Customer: Just that i spent 35 years working on medical xray equipment, and have a degree in electrical and mechanical engineering... I can fix nearly anything--but I'm always open for help!
Submitted: 17 days ago.
Category: RV
Expert:  Randall replied 17 days ago.

Hi! My name is ***** ***** I can assist you with this. I may need some additional information from you first in order to give a complete answer.

Customer: replied 17 days ago.
Okay...shoot.
Expert:  Randall replied 17 days ago.

The OEM control boards in these are not good quality and I suspect that this one is bad and that the fan relay is cooked. I would get a good after market board made by Dinosaur Electronics and install that in this and I suspect that will resolve this. That is called a "Fan 50 Plus" board. Sail switches and limit switches are pretty durable and only lint or pet hair in the sail switch usually cause issues there. Be sure that you check the LP working pressure in the tank regulator as that should be checked at least once a year. Shop around as the price varies for that board. Hope that helps here. Please get back to me if you need additional input as all follow ups are included in our fee.

Customer: replied 17 days ago.
Thanks, bud... I'll give that a try.
Expert:  Randall replied 17 days ago.

The timed delay relay may be defective as well, if you have the older style model. This was just about the time they changed this and put the relay on the board. Those, too, are available from Dinosaur Electronics. You can choose to upgrade to the Fan 50 board here if you want. The older board is called a UIB-S board from them. And you are most welcome! Please take the time to enter in a rating as that is the only way I get credit from the site for my time spent assisting you.