Heater Fan Motor

[Travler]

I was wondering if any of yall have had your heater Fan Motor run all the time? I have the thermostat turned all the way down and it does not matter if you are running on Batt or hooked to shore power.....it runs all the time. I need to figure out what's going on. So if you have any suggestions I am all ears.

[LiveTicker]

Please state your TM year/model and Furnace year/model. Does the burner also stay on? If you pull the fuse and replace it does it stop?

My new-to-me TM had that problem.
I bought a pre-owned 2002 last November and used a leaf blower to clean out all the outside vents, hatches, roof and storage.
When I got inside to test and clean everything, the furnace would sometimes cycle correctly and sometimes the fan would stay on for hours after a heat cycle.
I may have messed up or misalligned the sail switch.
I took it to an RV repair and it worked worked perfectly for them the first 6 times, then stuck on. They got me for a few hundred dollars for a circuit board.

My Suburban NT20SE furnace has 4 wires- 2 for power - 2 for thermostat.
The thermostat simply connects the 2 thermostat wires to START furnace. When wires are disconnected the furnace fire stops and fan does about a one minute cool down.
So a test is to disconnect themostat wires at the furnace and see if it cools down and shuts off - this will tell you if the themostat and/or wires to it are bad.
Just short the wires at the furnace for a while to start a cycle.

Also check is you have 12+ volts DC. Some things get flaky with low voltage.
Try disconnecting battery and unplug TM (or pull fuse) - may reset furnace.

That's all I can think of....

[Travler]

Please state your TM year/model and Furnace year/model. Does the burner also stay on? If you pull the fuse and replace it does it stop?

My new-to-me TM had that problem.
I bought a pre-owned 2002 last November and used a leaf blower to clean out all the outside vents, hatches, roof and storage.
When I got inside to test and clean everything, the furnace would sometimes cycle correctly and sometimes the fan would stay on for hours after a heat cycle.
I may have messed up or misalligned the sail switch.
I took it to an RV repair and it worked worked perfectly for them the first 6 times, then stuck on. They got me for a few hundred dollars for a circuit board.

My Suburban NT20SE furnace has 4 wires- 2 for power - 2 for thermostat.
The thermostat simply connects the 2 thermostat wires to START furnace. When wires are disconnected the furnace fire stops and fan does about a one minute cool down.
So a test is to disconnect themostat wires at the furnace and see if it cools down and shuts off - this will tell you if the themostat and/or wires to it are bad.
Just short the wires at the furnace for a while to start a cycle.

Also check is you have 12+ volts DC. Some things get flaky with low voltage.
Try disconnecting battery and unplug TM (or pull fuse) - may reset furnace.

That's all I can think of....

I have a 2007 2720 SD as for the furnace I will have to get back to you on that,but I will preform the above test and see what happens and then get back to you. I have already pulled the fuse and left it out for about 3 hours and put it back in and it started back running (Just the fan).

[Travler]

I have a 2007 2720 SD as for the furnace I will have to get back to you on that,but I will preform the above test and see what happens and then get back to you. I have already pulled the fuse and left it out for about 3 hours and put it back in and it started back running (Just the fan).

First this is a NT20S Furnace. This what I did. First I powered down the TM....no power at all for 24 hrs. 2nd I made sure the Batt was @ 12.5VDC
3rd I removed the wires from the furnace to the thermostat. Then I powered up the TM with Shore Power. The heater fan came back on and stayed on.

[MudDog]

I believe the furnance has a time relay in order to keep the fan blower blowing for awhile after the thermostat turns off the burner (to dissipate the heat build-up).

If, with the thermostat wires disconnected the fan comes on, but the burner stays off, it sounds like perhaps the relay is stuck. Does the fan come on immediately after re-connecting power?

You could probably try to test the relay with a multi-meter. It's supposed to power the blower when the thermostat calls for heat and then stay on for a time period after the thermostat signals a stop. But if the relay were stuck the fan could keep blowing.

This parts site lists a relay for your model furnance:

www.rvmarineworld.com/camping/pdf/suburban-furnace-parts.pdf

--jim

[Travler]

I believe the furnance has a time relay in order to keep the fan blower blowing for awhile after the thermostat turns off the burner (to dissipate the heat build-up).

If, with the thermostat wires disconnected the fan comes on, but the burner stays off, it sounds like perhaps the relay is stuck. Does the fan come on immediately after re-connecting power?

You could probably try to test the relay with a multi-meter. It's supposed to power the blower when the thermostat calls for heat and then stay on for a time period after the thermostat signals a stop. But if the relay were stuck the fan could keep blowing.

This parts site lists a relay for your model furnance:

www.rvmarineworld.com/camping/pdf/suburban-furnace-parts.pdf

--jim

Yes it comes on when the TM is powered up. I just talked to a dealer he said it could be the control board.....but I do think you may be correct about the relay. Now all I have to do is figure out where the relay is at so I can remove it and test it........any Ideas? Oh BTW Thank you.

[MudDog]

It is probably on the main board - depending on the year/board revision it may be soddered onto the board or it may be a plug-in relay that would be easier to replace.

The parts link had a rough sketch of what it looks like. Compared to everything else on the board, it will be fairly large and will likely be cube shaped and completely enclosed in plastic.

The relay will take input from the thermostat (which could be a 12V or could be a lower voltage) and that input will allow the internal switch in the relay to switch on or off. The internal switch is connecting or disconnecting power to the fan. It's a time relay so that there is a x second delay before the switch shuts power off to the fan.

So you have three connections on the relay:

1 signal connection (in this case from the thermostat)
2 power (12V)
3 output (the fan)

The signal from #1 is allowing #2 and #3 to connect. If that switch is stuck, you get a fan that won't shut off :)

If the relay is soddered on, it may be easier to replace the whole board.

If it's a plug-in, it should be easy to swap out.

[brulaz]

The fan in the NT-20-SE is directly controlled by the control board. The NT-20S is very similar to the NT-20SE, perhaps just a difference in how hot-air is ducted?

[Travler]

It is probably on the main board - depending on the year/board revision it may be soddered onto the board or it may be a plug-in relay that would be easier to replace.

The parts link had a rough sketch of what it looks like. Compared to everything else on the board, it will be fairly large and will likely be cube shaped and completely enclosed in plastic.

The relay will take input from the thermostat (which could be a 12V or could be a lower voltage) and that input will allow the internal switch in the relay to switch on or off. The internal switch is connecting or disconnecting power to the fan. It's a time relay so that there is a x second delay before the switch shuts power off to the fan.

So you have three connections on the relay:

1 signal connection (in this case from the thermostat)
2 power (12V)
3 output (the fan)

The signal from #1 is allowing #2 and #3 to connect. If that switch is stuck, you get a fan that won't shut off :)

If the relay is soddered on, it may be easier to replace the whole board.

If it's a plug-in, it should be easy to swap out.

On the 2007 2720SD the main board is located in the hall next to the bathroom/Shower......should be easy to find.......hope its a plug in.

[MudDog]

Just to clarify, the board in question should be within the heater itself - it's not part of the converter in the hallway.

Be sure you have all power/batteries (or fuses) disconnected before going anywhere near the wiring/heater circuit board.

Here's a link to a Suburban Furnance Parts manual with perhaps a better picture than the first link:

www.tada-rv.com/scripts/pdfretail/get.php?id=274

Look at the 'Delay Relay' on page 4 to see if you have it on your heater board.

[Travler]

Just to clarify, the board in question should be within the heater itself - it's not part of the converter in the hallway.

Be sure you have all power/batteries (or fuses) disconnected before going anywhere near the wiring/heater circuit board.

Here's a link to a Suburban Furnance Parts manual with perhaps a better picture than the first link:

www.tada-rv.com/scripts/pdfretail/get.php?id=274

Look at the 'Delay Relay' on page 4 to see if you have it on your heater board.

Thanks I will power down the TM so no accidents happen.

[Travler]

Just to clarify, the board in question should be within the heater itself - it's not part of the converter in the hallway.

Be sure you have all power/batteries (or fuses) disconnected before going anywhere near the wiring/heater circuit board.

Here's a link to a Suburban Furnance Parts manual with perhaps a better picture than the first link:

www.tada-rv.com/scripts/pdfretail/get.php?id=274

Look at the 'Delay Relay' on page 4 to see if you have it on your heater board.

Well I finally got to take a look at this heater relay and it's like I thought the relay is made to the board......I know it was Engineered that way to increase the makers bottom line...anyway I am just going to have it replaced by a dealer for insurance reasons........if it blows up atleast I will be covered.

[Wavery]

Well I finally got to take a look at this heater relay and it's like I thought the relay is made to the board......I know it was Engineered that way to increase the makers bottom line...anyway I am just going to have it replaced by a dealer for insurance reasons........if it blows up atleast I will be covered.

Electrical relays can be problematic due to the very nature of their design. The internal switch mechanism is a simple pair of brass contacts that come together and separate under high current. When the relay is activated, their is a spark (internally) arching can cause an extreme voltage spike. This spark will leave tiny deposits of carbon. Sometimes (even when fairly new) the contacts will stick and it may just be a one time thing. Other times, the contacts are actually welded together and no amount of tapping will dislodge them.

You might try taking the blunt end of a metal butter knife and striking the relay on the side. Not hard but sharply (I hope that makes sense). This will often dislodge the contacts and allow the relay to function normally. If it keeps happening, replacement may be desired. However, I would encourage you to give that a try before going to all he hassle of replacement. Sometimes the contacts are just barely sticking and need a little encouragment.....

You know the old saying, "If all else fails, hit it with a hammer"..... I think this is where that saying comes from.

[Travler]

Just to clarify, the board in question should be within the heater itself - it's not part of the converter in the hallway.

Be sure you have all power/batteries (or fuses) disconnected before going anywhere near the wiring/heater circuit board.

Here's a link to a Suburban Furnance Parts manual with perhaps a better picture than the first link:

www.tada-rv.com/scripts/pdfretail/get.php?id=274

Look at the 'Delay Relay' on page 4 to see if you have it on your heater board.

Electrical relays can be problematic due to the very nature of their design. The internal switch mechanism is a simple pair of brass contacts that come together and separate under high current. When the relay is activated, their is a spark (internally) arching can cause an extreme voltage spike. This spark will leave tiny deposits of carbon. Sometimes (even when fairly new) the contacts will stick and it may just be a one time thing. Other times, the contacts are actually welded together and no amount of tapping will dislodge them.

You might try taking the blunt end of a metal butter knife and striking the relay on the side. Not hard but sharply (I hope that makes sense). This will often dislodge the contacts and allow the relay to function normally. If it keeps happening, replacement may be desired. However, I would encourage you to give that a try before going to all he hassle of replacement. Sometimes the contacts are just barely sticking and need a little encouragment.....

You know the old saying, "If all else fails, hit it with a hammer"..... I think this is where that saying comes from.

Yeah I did try that.....believe me I did not want to spend that money,but thanks and yes your hint did make sense as I have about 31 years in the electronics industry.

[Wavery]

Yeah I did try that.....believe me I did not want to spend that money,but thanks and yes your hint did make sense as I have about 31 years in the electronics industry.

WOW!!!! You should be a valuable resource on this board.

The great thing about these discussions is that many more people learn from them than you might realise..........

Hope you got the problem fixed....:D

[Travler]

WOW!!!! You should be a valuable resource on this board.

The great thing about these discussions is that many more people learn from them than you might realise..........

Hope you got the problem fixed....:D

I am going to have the board replaced and should be up and going next week. As for people learning from these discussions.....I hope they do and if they need to know information concerning electronics all they have to do is ask.........I'll be glad to help them. And if they like organic cooking ingredients I do sell J.R. Watkins Products. You can see them @ http://richard-prewitt.blogspot.com/?spref=tw

[brulaz]

So where is the board and how do you get at it?

I though it was on the right side of the NT-20SE, but there's no opening there. Do you go in from the front? Or do you have to take the whole thing out ...?

[Travler]

So where is the board and how do you get at it?

I though it was on the right side of the NT-20SE, but there's no opening there. Do you go in from the front? Or do you have to take the whole thing out ...?

You have to take it out. The board is inside where the wires run into it. Be sure all power is removed before you do this. After I removed power I let it set overnight just in case their were any CAPS that needed to discharge.

[92cabby]

I was reading about your problem, and I looked at the furnace parts list. Low and behold, I spotted a bimetal thermal snap switch, called a “Fan Switch” on page 5 of the document. I’m not a furnace guy, and I haven’t seen a schematic of the furnace, but I think you should check the snap switch before you start throwing parts at it. If the problem is the snap switch it should only cost $5 or $10 bucks at the most, but I haven’t bought one in 20 or 30 years, so I could be wrong :) Your next question is going to be “Where is it located”. Duh, I don’t know, but it should be in a location where it can sense the temperature in the heat exchanger. The idea being that the fan won’t shut off until the heat exchanger cools to a certain temperature after a burn period. It should probably have the 12 volt source connected to one post and the other post connected directly to the fan motor. Or, just maybe, the snap switch output powers the coil of the delay relay, which is acting as an interposing relay, for that particular logic function. Like I said, I’m not a HVAC guy, and I’m just guessing. Bottom line, the snap switch would be a quick fix. Hope it works out OK.

[Redhawk]

What keeps the furnace from kicking on in cold weather when the TM is closed up? Is the 12V to the furnace on the same bathroom wall interlock button that the lights are?

We were camping last week and the thermostat was all the way down, 50 degrees I think, when the furnace kicked on. Yes it was cold out. Just got me to wondering....thanks.

[Scott O]

I very interesting point John. I recently noticed a small burn/melt mark on the inside of our front shell...where the exhaust would hit when the TM is down. This could conceivably cause a fire in the TM, along with the garage it is stored in and the house the garage is attached to... I have installed a Hunter digital thermostat, but don't know if the problem occurred before or after I did this. I am very careful to turn the thermostat off and remove it's batteries before storage.

[commodor47]

Scott,

A couple of thoughts: the furnace fan cycles through the ignition, run, and cool-down phase. Is it possible the cool-down phase was interrupted before the outside grill had cooled down? That could cause the burnt/melt mark you describe. As long as your propane tank(s) are turned off and the outside grill has cooled there should not be a concern for potential fire due to the furnace. I had one instance where the furnace fan kicked on after closing our TM. I had left the Hunter thermostat on and set for heat. Turning off the thermostat stopped the fan - as the furnace had already cooled down. Fortunately I always turn off the propane tanks prior to closing down the TM.

Dick

[rumbleweed]

Not sure on yours, but on mine the thermostat has a position ( detent) all the way to the left ( below lowest setting) that is actually a switch that turns it off.

[commodor47]

Bob,

The Hunter thermostat has a slide on/off switch behind the left side cover (http://www.trailmanorowners.com/forum/album.php?albumid=20&pictureid=73). I had forgotten to turn the switch to the off position - and had left the temperature set for 65.

Dick

[Scott O]

There were several things which could have caused my problem, all associated with "operator error"! We rarely use the coach heater, so close-down while warm was probably not a factor. I could have left the thermostat on (at a low temp), which is most likely the cause. I didn't used to turn off the propane while in storage, which could have contributed. Since the burn was on the underside of the front seal flap, no telling when or under what conditions it occurred as I didn't notice it for probably quite awhile. I think it should be emphasized in large print to be sure to turn off the thermostat and turn off the propane while the TM is stored. I suspect I got lucky, very lucky that more damage didn't occur...