Furnace trouble

[Kirk W]

The thing you need to understand is that the switch is one that is normally open, with an attached vane that is in the air path of the inside air of the furnace. When the furnace blower is moving enough air for safe operation, that vane will move against the switch actuator, closing it to allow 12V power to the circuit board which then sends power to the propane valve to open it and the power to the ignition probe to supply a series of sparks to light the flame. Even if the test did prove something, what it proves is that the switch is good but air movement was not enough without help to close that switch. That would mean that the furnace needs to be cleaned, as Chris and several of us have suggested, but that the switch is really good.

 

I have seen many RV furnaces fail to light because of the sail switch failing to open. I can only recall one bad switch but I have seen several cases where bugs built nests that interfeared with air movement cleaning allowed the switch to close and the furnace to work. I have also seen cases where the sail switch did not close because the furnace was running from the battery and the voltage was too low for the blower to run fast enough to move enough air to close the sail switch.

 

As Chris mentions, the sail switch has its vane in the air on the interior air side which supplies the heated air. It works fine that way because one motor is in the furnace with a blower on either end of the motor shaft, one moving combustion air through the furnace and the other moves air from the RV through the furnace to heat it and send it on to the RV ducts. That test, as hokey as it was, if proving anything it was that the sail switch is actually good.

 

In addition, you said that you have one of the Suburban SF series furnaces that have an outside access panel, as in the picture that I posted. If that is what you have then there is no need at all for the tech to pull your furnace out in order to replace a sail switch. You need to find a qualified tech to do your work. If you take it back to the guy who gave you that advice, you will no doubt pay for the switch, probably to have the furnace removed and maybe you will be lucky and he will clean out the offending bug nests that are most likely the actual problem with your furnace but your total bill will be far greater than it would be if you were to find a competent RV tech.

[aunut]

The thing you need to understand is that the switch is one that is normally open, with an attached vane that is in the air path of the inside air of the furnace. When the furnace blower is moving enough air for safe operation, that vane will move against the switch actuator, closing it to allow 12V power to the circuit board which then sends power to the propane valve to open it and the power to the ignition probe to supply a series of sparks to light the flame. Even if the test did prove something, what it proves is that the switch is good but air movement was not enough without help to close that switch. That would mean that the furnace needs to be cleaned, as Chris and several of us have suggested, but that the switch is really good.

 

I have seen many RV furnaces fail to light because of the sail switch failing to open. I can only recall one bad switch but I have seen several cases where bugs built nests that interfeared with air movement cleaning allowed the switch to close and the furnace to work. I have also seen cases where the sail switch did not close because the furnace was running from the battery and the voltage was too low for the blower to run fast enough to move enough air to close the sail switch.

 

As Chris mentions, the sail switch has its vane in the air on the interior air side which supplies the heated air. It works fine that way because one motor is in the furnace with a blower on either end of the motor shaft, one moving combustion air through the furnace and the other moves air from the RV through the furnace to heat it and send it on to the RV ducts. That test, as hokey as it was, if proving anything it was that the sail switch is actually good.

 

In addition, you said that you have one of the Suburban SF series furnaces that have an outside access panel, as in the picture that I posted. If that is what you have then there is no need at all for the tech to pull your furnace out in order to replace a sail switch. You need to find a qualified tech to do your work. If you take it back to the guy who gave you that advice, you will no doubt pay for the switch, probably to have the furnace removed and maybe you will be lucky and he will clean out the offending bug nests that are most likely the actual problem with your furnace but your total bill will be far greater than it would be if you were to find a competent RV tech.

Thanks!

[Jimalberta]

As a heating and AC tech for the last 46 years I have repaired many of these furnaces. Blocking the vent in my opinion does not confirm anything and in my mind would not point towards a failing sail switch. If anything I would think that blocking the vent slows down the incoming air past the burner and might be stopping a flame lift thus allowing a smoother ignition.

[aunut]

Thanks!

Update. I called Suburban in Tenn. The lady said she had not heard of that test. She also told me something that Camping World did not tell me (and I bought the coach new from them March 2014). All Suburban appliances have a 2 year parts and labor warranty for the original owner. It wouldn't cover insect problems, but would cover a defective sail switch. Wouldn't you think CW would know this? I don't believe it is the sail switch from what you guys have said, but if it was it it be under warranty. I called CW with this new info and am waiting for a manager to call. Not holding my breath.

[jc2]

And this is just one of "Many" reasons that I do not use CW.

[Kirk W]

Update. I called Suburban in Tenn. The lady said she had not heard of that test. She also told me something that Camping World did not tell me (and I bought the coach new from them March 2014). All Suburban appliances have a 2 year parts and labor warranty for the original owner. It wouldn't cover insect problems, but would cover a defective sail switch.

As I suggested before, I'd look for a different RV tech who actually knows what he is doing. As long as the RV tech is authorized to do warranty service for Suburban, it don't need to be the dealer who sold you the RV. I would suggest checking for a local mobile tech. It has been my experience that most of them are among the better RV techs out there.

 

I don't like to pick on CW particularly, but the guy you had either doesn't know what he is doing or he is a crook, or a bit of both. Some shops actually pay a sales commission to the RV techs for any parts that they sell, and I suspect that you just found one of them.

[rvtamer]

I tried to turn my Suburban furnace on this week (first time since last year) and it would not light. I followed the instructions and turned it on several times. I could hear the lighting mechanism clicking, but it would not light. I did notice wasps going in and out in July while on a trip.

The furnace is almost new and worked fine last time out last year. My hot water and fridge work fine on propane.

Do the wasps build a dirt nest and block the gas? If so, how do I clean it off? The access panel on the exterior is very tight and I didn't want to force it off after removing the screws.

From what you posted above, it does not sound like a propane issue because your other LP appliances are working under load.

The wasps you saw entering the furnace is most likely the problem. They build mud nest on all type of interior parts.

When an rv sets for a long time they (wasps) are attracted to the smell of lp, and can build quite a mud nest. I have found many nests that they have built attached to the motor and air wheels. This will either slow down the motor or prevent it from starting at all.

If the motor is slowing to less than 80 percent of its speed , the sail switch will not operate correctly and allow the circuit board to preform its functions, which allow the furnace to light up.

As for the rv tech testing the sail switch by covering the outside cover, that is a new one on me.

I have a little bit of experience with rv appliances, and that one ?

There is a test to see if you have power out of the sail switch to the circuit board that is very easy to do with a test light . I not sure why the tech didn,t use that to help figure out the problem.

 

As someone else said, most mobile rv service techs are the better ones , and I would seek one out to get your problem corrected.

[aunut]

From what you posted above, it does not sound like a propane issue because your other LP appliances are working under load.The wasps you saw entering the furnace is most likely the problem. They build mud nest on all type of interior parts.When an rv sets for a long time they (wasps) are attracted to the smell of lp, and can build quite a mud nest. I have found many nests that they have built attached to the motor and air wheels. This will either slow down the motor or prevent it from starting at all.If the motor is slowing to less than 80 percent of its speed , the sail switch will not operate correctly and allow the circuit board to preform its functions, which allow the furnace to light up.As for the rv tech testing the sail switch by covering the outside cover, that is a new one on me.I have a little bit of experience with rv appliances, and that one ?There is a test to see if you have power out of the sail switch to the circuit board that is very easy to do with a test light . I not sure why the tech didn,t use that to help figure out the problem.As someone else said, most mobile rv service techs are the better ones , and I would seek one out to get your problem corrected.

I have called a service tech recommended by Suburban. He agrees with everyone here that it should't be the sail switch and is probably a wasp nest. He is also going to charge much less than Camping World to clean it if it is. If it is a defect, he said it will be completely covered by warranty, which CW should have told me.

By the way, after I called CW and confronted them with all this, they said that the service manager would call me shortly. That was 8:30 yesterday morning. I haven't been contacted yet. I think I caught them with their hand in the cookie jar. After the new tech I have contacted confirms what I think he will, I am contacting CW headquarters.

[aunut]

Well, just left Camping World. The service manager finally called and told me to please bring it in and he would supervise it. The Tech recommended by Suburban couldn't get to it for weeks, so I gave CW another chance. It actually was the Sail Switch. No charge because Suburban paid parts and labor. I guess the test he used was not bogus. Go figure.

[Dreed917]

It would be nice if they would let you watch [they probably won't] the repair because afterward you wouldn't be an amateur anymore.

Dave 04 PleasureWay

[aunut]

It would be nice if they would let you watch [they probably won't] the repair because afterward you wouldn't be an amateur anymore.

Dave 04 PleasureWay

Even if I watched them, I would probably still be an amateur!

[rvtamer]

Well, just left Camping World. The service manager finally called and told me to please bring it in and he would supervise it. The Tech recommended by Suburban couldn't get to it for weeks, so I gave CW another chance. It actually was the Sail Switch. No charge because Suburban paid parts and labor. I guess the test he used was not bogus. Go figure.

 

aunut, I also wish they would have let you see how easy that test is for checking power out of the sail switch. It takes about 30 seconds or less ( hooking up a test light ) if you have access. You simply use a test light to see if 12 volt power comes out of the sail switch.

 

Someone earlier mentioned getting a service manual. These have flow charts that can help with diagnosing problems.

 

I glad you got your furnace fixed and thanks for letting us know what the problem was. Sometimes we don.t ever hear back from folks when the problem is resolved.

tim