Suburban SF-30 runs on Bench but blows fuse while installed

Thanks for the update. Glad you achieved success.

The issues are solved and furnace is now running.
1 Testing on the bench showed the ignitor nor the valve solenoid were activating. Further testing indicated although the sail switch looked to be operating, it was not closing the circuit in the up direction thus causing the rest of the issues. Tried lubricating spray but still failed. Replaced the sail switch.
2. The Previous Owner had also mixed up the fuses !! there was a 7.5 in the circuit that also runs the refrigerator, and i just assumed a 7.5 was the correct fuse 7 burnt fuses later. On the OEM panel called for a 10 amp fuse. Checking all the fuses revealed more fuses in wrong places.

Just now coming in from enjoying a cold beer sitting in a warm trailer in the driveway !!! Thanks for the suggestions here in this forum as they helped me troubleshoot the issues..

Have you taken a DVM and made SURE there is no continuity between the heater chassis and the +12V lead? You are inferring a short anytime its installed, and there are only a few ways for that to happen.

furnace is out back on the bench. the furnace never was removed from the metal housing.. saw the wires you mentioned. Checked wire.. no staples.

No Spark !! under any test... do you have to have pressure to the propane side.


so.. now what is sequence of testing? I purchased SAIL switch and Limit Switch, but have not replaced yet. I afraid it might be that circuit board contoller... i will try to see how much the motor draws.

Fiftybucks wrote:
just tried running furnace by bypassing all other connections. Blower starts, and runs for 2 min, exhaust is blowing out so that part is working but ignition fails, and shuts down. Apparently by bench test was not good, and going to pull it out again. What part / switch do i check for ignition?

On a SF30, the Hi limit switch wires go by the burner. IF those wires droop down and contac the burner, they will short out on the burner. THAT will cause the fuse to blow. When on the bench, if the furnace does NOT have the case removed from the RV, those wires will usually not short out until you reinstall it. IF that wire has been burnt and open that would cause a NO ignition. So, check those wires. Also, if the SAIL switch fails to close that will cause NO ignition also. Doug

just tried running furnace by bypassing all other connections. Blower starts, and runs for 2 min, exhaust is blowing out so that part is working but ignition fails, and shuts down. Apparently by bench test was not good, and going to pull it out again. What part / switch do i check for ignition?

Newman's suggestion has a lot of merit.

It would not hurt to also verify the current consumption of the furnace while being bench tested, or as installed but powered from an external supply. It's theoretically possible that it could operate but still have a problem causing it to use too much current, such as a partly shorted solenoid or some motor trouble.

7.5A fusing provides rather little overhead for the furnace, which (at least according to some pictures of the model online) is rated to use 7A. Assuming the wire going to the furnace is reasonably sized, I might try a 10A fuse if everything otherwise checks out. Obviously, doing that is at your own risk...but it would have to be a very poorly done installation for it to be dangerous. The Suburban installation instructions recommend a 12 gauge wire for the furnace power feed.

7.5 A may be too low..
If it's instantious, take an ohm meter and make sure that the box isn't somehow at +12v. That would instantly blow a fuse since the return path to ground could be through the LP pipe itself

Run a new wire to it good chance the old wire has a/staple in it