Furnace blower runs 24/7 2004 Journey 39

[jefflbi]

2004 Winnebago Journey 39K........ my issue (this week) is the blower for the floor vents never shuts off. It used to work just fine. I recently had the engine serviced, oil and filter change. I can't imagine that it was because of that............... However, on our last trip, on the way home I had to shut off the propane while on a ferry. I did not turn the thermostat to the off position before that, and I know that I've had the electric heat running while plugged into shore power at the house. Well I'm trying to lower the electric bill so I winterized the plumbing so I could turn the heat off. Through the manual I found out that the gas heat (furnace) uses the floor vents and electric heat uses the ceiling vents. I also found out that even if the thermostat is set to electric heat, the gas heat will kick in to help if needed. Everything should shut off when it gets up to temp, but for some reason the blower for the floor vents runs 24/7. I have tried everything I can think of to get it back in sync. I sprayed the thermostat switches with contact cleaner. I have set the thermostat to just gas heat, and the air will blow hot to get the coach up to temp, and then the air blows cold, and never turns off. I pulled the fuse on the thermostat and it still runs!!! I'm at a loss to figure this out.............
Update: I got a tip tonight to check and see if there is a sensor to make sure the furnace box is cooled down. My friend said that most heating systems will have a sensor in the blower box to make sure the box is also cooked down and that either the sensor might be bad or the relay for that sensor might be stuck.......... my manual did say there was more information about the furnace in the Owners Infocase, which I do have........... I'll be checking that next.....

 

[Morich]

You seem to be on the correct path but needing more definite info on the specifics of your furnace.
When I deal with an item on my RV, I often know some of the basics but find there are little details which are critical. Some of those small points are what the small item looks like and where to find it!

My path is to look at the labels on the furnace to get the correct model number, then do an online search for a troubleshooting manual for that furnace.
I would expect to find a manual with lots of detail and one section will be a specific path to take, using a flow chart.
There will also likely be a diagram to sort how the power flows to the blower motor, showing things like you mention.
Just from memory, I might think there is a thermostat like a small button type and it may not be working or it could be as drastic as the board needing changed.

But it is also ways cheaper and quicker to have a guide instead of just changing parts at random.

 

[jefflbi]

Yeah, I didn't think to put the make and model of the furnace in the OP and I guess there's a time limit on editing........... but it's a Suburban Gas Furnace Model SH-42.

I found several documents on the internet and one has a troubleshooting flow chart. Now whether I can understand it or not is another challenge........

 

[Morich]

With that info, I find this site which seems to be one I've liked!
https://techsupport.pdxrvwholesale....urnace-Master-Service-and-Training-Manual.pdf

It seems the fan may be at the first part of the process, so maybe not too far to search.
Some ideas to kick start the testing?
Page 26 for starting?
I can't say where these [points are found on each furnace so it will take some looking at their drawings and pictures to spot the correct points but it should be a place to start and help to make sure you don't look past a problem.

Click this snip for better view!


It's a trek at times, so I'll wish you luck and let you check for a few things. The wires and connections on RV are often prone to getting corrosion and some cases are as simple as letting them fix themselves when we pull a connection apart and put it back. That can clear the corrosion and we look like a genius without even knowing what happened!
Best of luck and let us know how it goes!

 

[jefflbi]

Yeah that's the same manual I found........ Thanks

So I see there is something called a Sail Switch, but so far I can't find it in the diagrams. Can anyone point me to where it might be located??

 

[jefflbi]

I wonder if the fact that my propane is low could be a factor?? It only reads 1/3 full.......

 

[tim myers]

The sail switch is there to prove airflow so your burner will light. If the sail switch was bad you would never have heat. Like most gas or propane furnaces there is usually a thermocouple somewhere that reads the air temperature. When you shut down a furnace the fan keeps running till the air temp has dropped below a specified temperature, then the circuit opens and the fan shuts off. I saw a reference to a 15 second timer, and while that may be how they run, I would be surprised by that. In either case if the fan keeps running either the thermocouple is bad or the timer is bad cause the fan keeps running after the air is cooled down. Just my $0.02

 

[Morich]

Ok, got more ideas of what is needed to find!
This is from page 13 and maybe as close as needed, even though not the SH-42 model?
Click to get a better picture or go direct here:
https://techsupport.pdxrvwholesale....017/09/Suburban-Furnace-Master-Parts-List.pdf


When looking from the outside, there should be wires coming from the thermostat. If the thermostat is stuck closed, the furnace will keep blowing as it thinks heat is wanted!
So if you take on of the thermostat wires loose, either at the furnace or inside at the thermostat, the blower may stop. If it stops, that may be telling you that the thermostat is not opening when it gets warm!
At the thermostat, you may find there are a bunch of small wires that go into the wall 6-8 inches and then have a connector of some type where they meet different colored wires, so don't let the wire colors mess with your mind!
Open one and see if the blower stops?

The move to outside and look for the sail switch and a different type thermostat. They are both small with the sail of the switch stuck inside where the air moves so you may only see the back side of a small microswitch that the sail connects to with two wires.
This link gets a lot of pictures of different sail switches and also videos of testing or replacing them. Maybe worth a look at some for general idea in pictures?
There are also limit switches or the small thermostat I mention. Too hot, it opens until it cools but about all you see on the outside is the back with two wires!
https://www.google.com/search?q=RV+...gwMzdqMGoxNagCALACAA&sourceid=chrome&ie=UTF-8
You want the sail switch to be open when blower is not running but when it blows the sail, we want it closed! Idea is that if the air is not moving enough it doesn't let gas into the furnace!
Then next in line is the little button thermostat which is closed if everything is normal but if the furnace gets too hot, it opens and shuts the gas off!

So red wire to black wire, should be open until blower is on then very low resistance if the sail is moving!
Then from the black wire to white wire on other side of limit switch/ button thermostat should always measure really low resistance, except it nearly burning the RV down!

Sometimes just wiggle these push on connections will clean them enough to make things work??

The timer is to give time for the fire to light. It keeps the circuit made long enough to open the gas valve, light the fire, etc but if the fire doesn't light in 15 seconds the timer shuts off the gas again!

Some will do this three times and then go into "lockout" for some set amount of time.

Thermostat closing starts blower,
blower running closes sail switch
After a time, gas valve opens and ignition should happen

The flame then is sensed and then continue until the thermostat opens when it gets warm enough and closes the gas solenoid. This is where we have to find out why it doesn't make the thermostat happy and shut down?
Blower then runs until cooled and shuts off!

Maybe the thermostat contacts are stuck shut? Maybe a bad board or one of these small parts?

 

[jefflbi]

An RV tech on youtube said that the control board most likely has to be replaced. If what I'm finding on Amazon is the correct replacement, they are less than $60. But the parts list I downloaded from the same site as the service manual is confusing as to which board it is...........It tells me the page for parts for SF-42 and when I go there it's eithers PS30 or NT40. I'm certain that my heater is 30,000 btu......... which would lead me to think PS30 is my parts list.........

Anyway I was able to get the fan to stop blowing by disconnecting one of the negative terminals on the coach batteries. A different RV tech, who I've actually worked with over the phone, suggested that I remove the fuse for the heater blower for a few minutes and then put it back on. Well the fuse box that contains that fuse is a pain in the ass to get to so I figure disconnecting the battery was the next best thing........... plus it's dark, wet and damp here, and I'm getting a chest cold......... I'll reconnect the cable tomorrow, get my propane tank filled and go from there..........

 

[Morich]

One of the big problems with RV tech is the way they seem to go for the biggest, most expensive parts to change first! It may be true that they find the board is the most common failure but I also know that while they are changing out the board, they also take many of the connections loose and put them back together.

So when they say the board was the problem, do they really know that or is it just taking the wires loose and getting them cleaned up?
one of the benefits of going through the troubleshooting process, step by step is that it should actually tell you what part is bad.

But that is not what makes the most money if your business is selling parts!

But as a side issue, the propane will not cause the blower to keep running, so that is not the main problem.
But it's always good to have a full tank at this time of year!

 

[RGVTEXAN]

Maybe check the Thermostat fan switch. it should be in Auto, not Run.

 

[jefflbi]

Maybe check the Thermostat fan switch. it should be in Auto, not Run.

It's set to auto..........

 

[jefflbi]

One of the big problems with RV tech is the way they seem to go for the biggest, most expensive parts to change first! It may be true that they find the board is the most common failure but I also know that while they are changing out the board, they also take many of the connections loose and put them back together.

So when they say the board was the problem, do they really know that or is it just taking the wires loose and getting them cleaned up?
one of the benefits of going through the troubleshooting process, step by step is that it should actually tell you what part is bad.

Just an FYI I did redo all the connections at the furnace and I sprayed contact cleaner on them as well. Now that I know where the blower is, I'm going to do the same thing as soon as I'm feeling better, and I'll replace that sail switch at the same time.........

 

[Morich]

One thin to know avout the sail switch is how simple it is. The "sail" is just a small metal piece that blows as the air moves and as it moves the metal is bent so that it makes contact with the little button on the microswitch! It pushes the switch or not!
One of the things that can happen is that something like hair from pets or spider webs, etc. bunch up around the sail and it doesn't move right!
Whether it looks exactly l8ike this model shows or not is still a guess but there are not lots of small things that have two wires on them and it will be inline with the little button thermostat, so may take the sail switch out and see if it looks like it can move to click the tiny little switch.

Since the problem is that the blower is running too much, we can be pretty sure the little thermostat is closed as it should as it only opens if things get way too hot and we need it to do an "emergency gas shut off!

 

[7997redtail]

Hey jefflbi.

Im really liking Morich's thought process and think you will find your problem faster by....getting better and trouble shooting before buying parts.

As a last thought, please let us know what the fix was when done. I hate threads that never get a conclusion

Thanks

 

[jefflbi]

Well I replaced that sail switch and it did not fix my problem. But let me tell you it was a royal pain in the ass getting the panel off that covers the heater/blower. The last guy used some sort of black weather proofing sealant and it makes no sense. That panel should come off easily. And it's already under a latched panel so why use that sealant?? I had to use a big ass screwdriver to pry it up and I bent the panel in the process. I got a lot of scraping to do to remove all that black crap, which will not be going back on. At most I'll use some thin weather stripping. Anyway I wound removing the whole heater/blower assembly so I could get at the circuit board, which is the only other part to replace, and I found one on Amazon for under $200 so I ordered it. There is an on/off switch connected to the circuit board and I have no idea what it's function is. It was set to on when I first removed the panel and turning it off did not turn the blower off. I'm attaching a picture........... you can just see the switch at the top of the picture...........

 

[jefflbi]

ISSUE RESOLVED!

Replacing the control board was the answer. Under $200 on Amazon........