Atwood furnace not working, random problem with the fan blower

[Jill]

I've read through all the furnace threads and haven't seen a problem quite like ours so starting a new thread.

We are on the coldest trip we've ever been on and are having random problems with our 7 year old Atwood furnace. Occasionally we get lucky and it turns on and runs for a while. Most of the time it doesn't work at all. We are running on shore power. I tried disconnecting and have the same issues when running off the battery.

We turn on the thermostat and hear a click. A few seconds later the furnace clicks. Then nothing happens at all. The blower does not come on. We get the 'Airflow/Limit switch' indicator. I'm thinking that's because there is no air flow at all due to the blower not coming on. I used our high pressure air duster on it in various places and sometimes that helped it start, other times not.

On those rare occasions where it works, sometimes you can hear the fan changing velocity, and most times the furnace suddenly shuts down before reaching the desired temperature.

From reading the other threads I'm thinking it could be an electrical issue, insufficient power to start the blower and keep it running? All other electrical components are running fine. We’ve looked for loose wires and nothing was obvious. Or it could be we just need a new fan motor. We haven’t removed the housing and looked inside though as it appears to be a big job. We have a multimeter with us and will check to see the power coming in if we can figure out where to check it.

Either way we’ve decided to continue our trip (4 more weeks) best as we can with portable heaters and have a tech look at it when we get home. I posted this here though in case anyone thinks there is anything else we can try. Thank you in advance!

[splitting_lanes]

It sounds like a control board issue from your description.

Maybe one of the people on this forum with far more experience with the furnaces than I will chime in.

[DT6]

Have you checked the red light on the control board (assume there is one). Your furnace manual should have some type of chart that tells you want a particular red light blinking sequence indicates. I've also had good luck calling Dometic directly, or you can email them.

You may also want to check the thermostat to verify that it is not the cause, and of course the infamous sail switch (try a new one if you have not recently).

Sail Switches are relatively cheap, I think the control boards go for $130 to $150 or so, and I don't know what thermostats cost. I'd advise some research prior to ordering any parts to see if they are returnable. Most electronic parts are not, so if I were doing this myself, I'd check the control board to see if I had a blinking light sequence I could observe, then I'd call Dometic to discuss my issue and what I found, then buy the part that is the most likely culprit.

It sounds like your taking excellent care of the unit, so best wishes on a successful diagnosis and repair!

[SRS]

Originally Posted by Jill

I've read through all the furnace threads and haven't seen a problem quite like ours so starting a new thread.

We are on the coldest trip we've ever been on and are having random problems with our 7 year old Atwood furnace. Occasionally we get lucky and it turns on and runs for a while. Most of the time it doesn't work at all. We are running on shore power. I tried disconnecting and have the same issues when running off the battery.

We turn on the thermostat and hear a click. A few seconds later the furnace clicks. Then nothing happens at all. The blower does not come on. We get the 'Airflow/Limit switch' indicator. I'm thinking that's because there is no air flow at all due to the blower not coming on. I used our high pressure air duster on it in various places and sometimes that helped it start, other times not.

On those rare occasions where it works, sometimes you can hear the fan changing velocity, and most times the furnace suddenly shuts down before reaching the desired temperature.

From reading the other threads I'm thinking it could be an electrical issue, insufficient power to start the blower and keep it running? All other electrical components are running fine. We’ve looked for loose wires and nothing was obvious. Or it could be we just need a new fan motor. We haven’t removed the housing and looked inside though as it appears to be a big job. We have a multimeter with us and will check to see the power coming in if we can figure out where to check it.

Either way we’ve decided to continue our trip (4 more weeks) best as we can with portable heaters and have a tech look at it when we get home. I posted this here though in case anyone thinks there is anything else we can try. Thank you in advance!

Your problem sounds similar to one describe in a video from Darren of My RV Works. The furnace clicks but nothing happens. While diagnosing the problem, Darren jiggles a wire and the fan comes on. The internal wiring of electric motors can go bad with age creating a dead spot in the windings. It could also be your not getting enough power to the heater. Unfortunately, it could be a number of things. If you use the heater a lot on your camping trips and considering the age of your trailer, the motor might be a good bet.


The two video below are long but very instructive. It could also be the power board but not necessarily.

https://www.youtube.com/watch?v=JFEZrs4_t6I&t=394s

https://www.youtube.com/watch?v=F0l2avqFL5U

[Centex]

Originally Posted by Jill

I've read through all the furnace threads and haven't seen a problem quite like ours so starting a new thread....

Hopefully your search led to this thread by David Murphy and the 2015 Atwood furnace troubleshooting document linked in his 4th post

Wishing you good luck!

[Jill]

Originally Posted by DT6

Have you checked the red light on the control board (assume there is one). Your furnace manual should have some type of chart that tells you want a particular red light blinking sequence indicates. I've also had good luck calling Dometic directly, or you can email them.

You may also want to check the thermostat to verify that it is not the cause, and of course the infamous sail switch (try a new one if you have not recently).

Yep checked the red light, that's how I got the 'airflow/limit fault' error. And checked the thermostat. Have done more research and at this point we think the fan motor needs replacing.

[Jill]

Originally Posted by SRS

Your problem sounds similar to one describe in a video from Darren of My RV Works. The furnace clicks but nothing happens. While diagnosing the problem, Darren jiggles a wire and the fan comes on. The internal wiring of electric motors can go bad with age creating a dead spot in the windings. It could also be your not getting enough power to the heater. Unfortunately, it could be a number of things. If you use the heater a lot on your camping trips and considering the age of your trailer, the motor might be a good bet.

Thank you that video was really helpful! We are going to start with replacing the fan motor, but probably not until we return from our trip. Whatever happens, we will post back the resolution, in case any one else runs into the same problem.

[Jill]

Originally Posted by Centex

Hopefully your search led to this thread by David Murphy and the 2015 Atwood furnace troubleshooting document linked in his 4th post

Wishing you good luck!

Yes I found that and the tech manual he referenced all very helpful. This is such a great forum!

[John in Santa Cruz]

If you take it apart far enough to get to the motor wiring, you should be able to disconnect the motor and jumper it to a 12 volt power supply or batteries, and if the motor is good it should spin. If the motor does not spin when directly jumper to power, then it's definitely a bad motor. The motor draws a couple amps so make sure you don't use wire that's too skinny.

[Jill]

Originally Posted by John in Santa Cruz

If you take it apart far enough to get to the motor wiring, you should be able to disconnect the motor and jumper it to a 12 volt power supply or batteries, and if the motor is good it should spin. If the motor does not spin when directly jumper to power, then it's definitely a bad motor. The motor draws a couple amps so make sure you don't use wire that's too skinny.

Will try that - thank you!

[CE Vogel]

Originally Posted by Jill

Will try that - thank you!

While you have the motor out, put a drop or two of oil on the bearings.
Your symptom description sounds very much like you have a worn out fan motor. A little oil may get you home.

[Jill]

Originally Posted by CE Vogel

While you have the motor out, put a drop or two of oil on the bearings.
Your symptom description sounds very much like you have a worn out fan motor. A little oil may get you home.

Will do, thanks!

[John in Santa Cruz]

Originally Posted by John in Santa Cruz

If you take it apart far enough to get to the motor wiring, you should be able to disconnect the motor and jumper it to a 12 volt power supply or batteries, and if the motor is good it should spin. If the motor does not spin when directly jumper to power, then it's definitely a bad motor. The motor draws a couple amps so make sure you don't use wire that's too skinny.

oh, also, after unplugging the motor, put a volt meter on the pins that feed the motor and try and start the furnace, see if there's 12V there.

[Wakefido]

Had the same problem so cleaned the sail switch that seemed to help for a few hours but not permanently. Finally replaced the sail switch ($30) which solved the problem.

[LarryB.]

Check your furnace’s external exhaust flue and check your sail switch.

I believe that the “logic” in the furnace’s control system is similar to the “logic” in home power-vent water heaters:
(A) thermostat sends start-up “trigger” to control board
(B) then the control board:

1. starts exhaust fan
2. waits for sail switch to close
3. opens gas/propane valve
4. briefly waits
5. initiates sparking sequence and waits
6. detects that ignition has occurred (heat)
7. stops sparking sequence
8. waits for thermostat to send shut-down “trigger"

If there is dust in/around the sail switch or if the exhaust flue is clogged the control board will stop at step #2. If gas/propane isn't available, the control board stops at step #5.

[Jill]

Originally Posted by LarryB.

Check your furnace’s external exhaust flue and check your sail switch.

I believe that the “logic” in the furnace’s control system is similar to the “logic” in home power-vent water heaters:
(A) thermostat sends start-up “trigger” to control board
(B) then the control board:

1. starts exhaust fan
2. waits for sail switch to close
3. opens gas/propane valve
4. briefly waits
5. initiates sparking sequence and waits
6. detects that ignition has occurred (heat)
7. stops sparking sequence
8. waits for thermostat to send shut-down “trigger"

If there is dust in/around the sail switch or if the exhaust flue is clogged the control board will stop at step #2. If gas/propane isn't available, the control board stops at step #5.

Thanks but for us even step 1 doesn't work. That fan never starts so we don't think it is the sail switch (but we've cleaned it just in case). However we've not tried cleaning the exhaust flue. Will try that tomorrow.

[Ooshkaboo]

Originally Posted by Jill

Thanks but for us even step 1 doesn't work. That fan never starts so we don't think it is the sail switch (but we've cleaned it just in case). However we've not tried cleaning the exhaust flue. Will try that tomorrow.

Cleaning the switch doesn’t always work, I’d start off with a new one.
Then check into the limit switch.

[SRS]

Originally Posted by Jill

Thanks but for us even step 1 doesn't work. That fan never starts so we don't think it is the sail switch (but we've cleaned it just in case). However we've not tried cleaning the exhaust flue. Will try that tomorrow.

I'm not an expert on this subject, but my heater fan comes on withing just a few seconds of the thermostat clicking on. Your heater hasn't started the sequence suggesting either a bad fan motor or a power board failure. Because so many people experience heater problems, I've watched lots of videos on the subject. Darin of My RV Works has a number of them that might help you figure this out. Here's a link to just one of the videos.

https://www.youtube.com/watch?v=F0l2avqFL5U

[NEWYORKHILLBILLY]

Originally Posted by SRS

I'm not an expert on this subject, but my heater fan comes on withing just a few seconds of the thermostat clicking on. Your heater hasn't started the sequence suggesting either a bad fan motor or a power board failure. Because so many people experience heater problems, I've watched lots of videos on the subject. Darin of My RV Works has a number of them that might help you figure this out. Here's a link to just one of the videos.

Thanks for posting he has a lot of good info.

[bdornbush]

I had a similar problem. The fan motor would start and then after a few seconds, the fuse blew. My mobile repair tech checked the motor and found a spot where the motor dragged ever so slightly. He replaced the motor and the problem was solved. The key to me is that the motor speed varied prior to this, indicating to me that something was wrong with the motor.