Furnace sail switch

[Kenmartin1]

I have a 96 thor residency 36' motorhome that has been sitting for a few years. Has front and rear furnaces, ignition style atwoods. Upon starting, both furnaces fan's run strong, but wouldn't light. I bypassed the sail switch and both furnaces operate properly. I removed a sail switch and tested it for continuity, and it works! My fans seem to be blowing strong out of all floor vents... Do these switches get stiff or stuck when old???

One other question: I can find a power transfer switch, or converter, if anyone knows where they may be hidden. Thanks, Ken

[Coyote74]

Thanks for the answer to my question on pb! jhilley. I thought about electrical contact cleaner.
Never heard of pb.

[Dutch_12078]

I've repaired several furnace issues over the years where the failure was caused by kitchen grease buildup on the sail switch blade. The sticky grease and dirt buildup made the blade enough heavier that the sail switch either didn't operate at all, or only operated when the fan spun up higher at peak voltage from the converter. A common complaint in that situation was that the furnace worked okay on shorepower, but not on battery power.

[jhilley]

Coyote74 wrote:
What is pb?

It is PB Blaster

[Jagtech]

Kenmartin1 wrote:
I have a 96 thor residency 36' motorhome that has been sitting for a few years. Has front and rear furnaces, ignition style atwoods. Upon starting, both furnaces fan's run strong, but wouldn't light. I bypassed the sail switch and both furnaces operate properly. I removed a sail switch and tested it for continuity, and it works! My fans seem to be blowing strong out of all floor vents... Do these switches get stiff or stuck when old???

Thanks, Ken

Sail switches are basically a sensitive microswitch. They do become "flakey" or intermittent before failing completely. A continuity test may indicate they are good, but that isn't the best test. The contacts inside the switch become corroded or dirty, and when operated by hand they will often test good. Using a DMM on a low-ohms scale, you will likely see the resistance of the switch bouncing around from a few ohms to several hundred ohms. If the furnace works fine with the switch bypassed, then replace it.

[Coyote74]

What is pb?

[Kenmartin1]

I tracked down the power draw by placing the meter between the battery ground wire and its post, to measure the draw. Then followed power wires back from the battery. Everywhere power split, I removed each wire until the power draw was gone. I have a box of relays on my engine compartment, and by disconnecting one wire there, the power draw is gone. Now I have to figure out where that wire goes...however, everything on the coach seems to work! Ken

[YC_1]

Four volts in an hour would be a massive draw. I highly suspect you have sick batteries.

[Kenmartin1]

One in the front cabinet, maybe just to run the tv.

[YC_1]

Do you have an Inverter?

[Kenmartin1]

Thanks. I'll keep looking. I have a large power draw... My coach battery lost 4 volts in an hour. I put a test light in between the negative cable on the battery, and it lights up bright. I removed the 12 v fuses but the light stayed on. Anyone have ideas of power drains that do not go through the fuses?

[John_Wayne]

The transfer switch if you have one should be close to where the power cord comes into the MH. the converter could be any where. mine is in the basement a friends was under the refrigerator where you couldn't see it unless you removed a panel.

[turbojimmy]

Kenmartin1 wrote:
Yc1, you were correct... Upon starting the engine, it's alternator put out enough power for the furnaces to light and put out heat. I realized the coach batteries were run down, and there is a power draw competing for the furnace power.

Thanks for the follow-up. This is good to know!

[Kenmartin1]

Yc1, you were correct... Upon starting the engine, it's alternator put out enough power for the furnaces to light and put out heat. I realized the coach batteries were run down, and there is a power draw competing for the furnace power.

[YC_1]

Kenmartin1 wrote:
Thanks, I'll try the pb. I have really good batteries.

You may have great batteries but 12 volts has very little push and a loose connection along the line will drop the voltage quickly. You really need to know the voltage at the furnace with it running so there is a good load on it. Better yet, run them both and test. A poor ground will give you the same low voltage.