Another LP Furnace problem...

[Moder2]

Furnace guy just called...

Again can't find anything wrong, it doesn't trip on the bench.

He says the fan speed is fine. Checked the burner again, and there are no obstructions and it is burning clean and the way it should.

Called Suburban, and they are also in his camp that it must be a venting problem. Again I don't see how since it is a new problem, and worked fine last year... And there are more square inches and vents than they recommend.

I checked the ducts as best I could with an inspection mirror, and still see nothing obstructed. Acutally found a couple MORE outlets in the bays I didn't know about, so again I am not sold on this at all. repair company is saying they have done all they can do, either live with it or cut in more vents.

My voltages are fine.

This is just frustrating.

We have one more idea, and that is the furnace might not have been seated properly against the plenum, and it is sucking in hot air from the return.


John

[DonavonP]

You can "prove" the lack of vent volume by putting fans over your heater vents sucking air to reduce the back pressure on the furnace fan motor. If that cures your problem, you need a new fan motor. Bench testing the furnace fan with no back pressure doesn't seem like a real world test.

Your electric cube heaters would probably work for vent test.

Graingers might be able to supply you with a larger, more durable fan motor.

[Moder2]

I thank all of you for your suggestions.

Furnace is back in and working properly. We must have gotten a bad batch of limit switches is all we can determine. We picked up a 4th switch from a local dealer and bingo, it is operating as it should. We came to the conclusion it had to be the switch because we pulled the unit out as soon as it hit limit, hit the back if it with an IR gun and it wasn't near 160 degrees.

It hasn't hit limit yet, and has risen the room temp to 78 degrees now. All this screwing around for that... Ugh.

The repair company did make good. They did not charge me for the subsequent calls, even though the tech was here most of yesterday and another hour today.

John

[KIX]

John, Glad you found the problem adn got it fixed.

[RV Wizard]

John, good to hear you have resolved the problem. Who supplied the limit switches, Suburban or another vendor?

[Moder2]

The original was OE, the following two came directly from suburban. The final switch was after market, but I am not sure who made it. It is funny, because initially I made them order the OE switches cause in the suburban manual it states how important it is to use OE parts. Ugh.

Still working fine and Dandy.

Suburban was very insisitant that it was air flow issue also. I tried to explain to them that it was working fine two weeks ago, and this was a new symptom. I guess no body expects to get 2 bad replacement switches, but a bad run can happen I guess, I am sure Suburban gets them from another vendor?

John

[Jeeperrmartin]

Boy that is not saying much on the quality control on those limit switches. I once bought a new battery, and the new one worked worse than the old one.

Logically you think it is something else since the replacement is a new part. You don't expect the new part to be bad, and for sure not 3 more in a row.

Happy heating!!!!!