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flbill · 12-30-2022, 09:59 PM

2018 ACE 30.3 - newer to us.

Been testing the heat the last few weeks and discovered an issue I hope someone has some insight on.

Heater runs fine, but after a few minutes it acts like it hit its hit the temp set on the thermostat (but doesn't) and shuts off. Then never comes back on unless I switch the wall thermostat to off, and then back to heat.

I did discover the bedroom vent was not connected (maybe since birth) and I thought maybe that was causing the unit to overheat (vented to the heater compartment rather than the vent to the bedroom) but that is now fixed and no change.

This only happens with the heat. A/C seems fine - same thermostat.

EDIT:
Propane is on and bled via the stove.
Checked the air flow thing - clear and not obstructed.
Reset the system and checked what I could.
Batteries connected and generator running.

B

triplewide · 12-31-2022, 05:25 AM

My guess would be that the problem is not in the thermostat. The furnace may be overheating and the high temp cutout is opening. Private message OldBiscuit. He can tell you what to do to check it out.

On my ACE the furnace ducts were kinked restricting air flow causing it to overheat.

Youtube video:

https://youtu.be/J_bUQbIIP1U

flbill · 01-01-2023, 09:02 AM

Thanks for the reply.
Great video!

I will take a deeper look at the ductwork.
I do know that the one to the read bedroom (that was disconnected) is kinked as it runs behind the pocket door and shower - and with the door open it presses it in. Will have to disfigure myself to try to reroute something there...

I'll followup with the message you suggested if rerouting does not change anything. And post results here.

One question in my head though - if it is overheating (which is likely) - why would turning it off and then immediately back on via the thermostat restart it. I would think overheating would require some time to cool down... although the fan does blow at start up and shut down - so that may be why....

flbill · 01-01-2023, 02:18 PM

I went back and checked all the hoses - opened the inside and outside vents and opened the door that was hitting the one hose.

Fired up the unit - full heat for 8 minutes, then shut down.
I turned up the thermostat to verify things, and never came on.

Turned the thermostat off, and then back to heat - furnace came on like it should - and ran about 8 minutes and then off again.

This time though I had the cover off outside and before doing anything I checked and found a fault code. 3 flashes = ignition lockout fault.

Now more research.
We do have a warranty on it, but these days it takes forever to get someone to look at it - and then repair it. I want to see what I can do first.

triplewide · 01-02-2023, 04:45 AM

I PM'd Old-Biscuit. What brand is your furnace?

I diagnosed mine by bypassing the sail switch, then the thermal cutout to see which, if either was causing the shutdown. Also checked them with a meter.

Sunrise Camp · 01-02-2023, 06:18 AM

Try checking / cleaning your sail-switch. It was super-easy for me. See this:

https://www.youtube.com/watch?v=Z-jrrLDxnFQ&t=14s

triplewide · 01-02-2023, 05:11 PM

I sent Old-Biscuit the wrong link, he should be able to find you now

Old-Biscuit · 01-02-2023, 08:41 PM

Quote:

Originally Posted by flbill

I went back and checked all the hoses - opened the inside and outside vents and opened the door that was hitting the one hose.

Fired up the unit - full heat for 8 minutes, then shut down.
I turned up the thermostat to verify things, and never came on.

Turned the thermostat off, and then back to heat - furnace came on like it should - and ran about 8 minutes and then off again.

This time though I had the cover off outside and before doing anything I checked and found a fault code. 3 flashes = ignition lockout fault.

Now more research.
We do have a warranty on it, but these days it takes forever to get someone to look at it - and then repair it. I want to see what I can do first.

Ignition Fault Lock out.......that is what is called a 'soft lock out'
It will self clear after 1 hour

Turning Thermostat Off then back on starts fan which has to do a Purge Cyle before DC can be sent to circuit board for a trial for ignition.

Running for 8 minutes then shutting down does suggest Hi Temp Limit Switch Opening and the restart of Fan blows enough airflow to cool it back down where the Limit Switch recloses allowing for reheating cycle

Questions:
*Have you checked the intake/exhaust vents for obstructions?
*When furnace shuts down after the 8 minutes does Fan continue to run of does it shut down at same time burner shuts off?
*Room air/ducts......obstructed-blocked will cause overheating
*Return air path...items stowed obstructing/blocking return airflow to furnace will cause overheating

**Fan....continues to run or shuts off at same time is a CLUE

Model of your Atwood?
*Atwood has the Fault Codes

triplewide · 01-03-2023, 03:50 AM

Thanks Old-Biscuit

flbill · 01-03-2023, 06:58 AM

Thanks for the info.
I will head down to storage today and follow up with you this afternoon.

*Have you checked the intake/exhaust vents for obstructions?
--> Yes. But will double check today.

*When furnace shuts down after the 8 minutes does Fan continue to run of does it shut down at same time burner shuts off?
--> Fan continues to run.

*Room air/ducts......obstructed-blocked will cause overheating
--> Not that I could tell, but will double check today.

*Return air path...items stowed obstructing/blocking return airflow to furnace will cause overheating
--> Clear. It is under the fridge, and opens to hallway.

**Fan....continues to run or shuts off at same time is a CLUE
--> Will verify. But I believe it stays on.

Furnace is: 35,000 BTU, AFMD35141 (VER.4-32835)

triplewide · 01-03-2023, 09:59 AM

If you are familiar with the furnace and electrical, you could use a meter to check for voltage in and out (12 volts I believe)of the high temp limit when you turn the furnace on after sitting for awhile. When the flame cuts out and fan is still running, check again for voltage in and out. If voltage in and no voltage out then the limit is tripping. Could be the limit is weak or some issue is causing the furnace to overheat. Or you could bypass the limit and see if the furnace continues past the "8 minute mark". Just don't run too long and overheat the furnace. You could also bypass the sail switch to see if it is tripping.

Is there a filter at your return air grill?

Was the furnace working when you stored it last? If so, some critter may have caused obstruction to air flow through the ducts, combustion exhaust air, or fouled the sail switch. Includes bees, spiders, etc.

Old-Biscuit · 01-03-2023, 10:05 AM

Fan stays running indicates Hi Temp Limit Switch is OPENING vs bad circuit board

Turning Thermostat Off/Back On and furnace working ----- restarts furnace sequence (Fan staying running allows for Hi Temp Limit to Cool off & close so normal startup sequence can occur)

**When it trips/fan stays running..........if you wait does furnace start backup or does fan shut off after 5 minutes?

Why is Hi Temp Limit Switch opening/heat exchanger overheating?
Airflow........
Low DC Voltage...fan motor not coming up to full speed (enough to close sail switch but not enough airflow to remove heat)
Loose air wheel ----- broken vanes
Obstructed Intake/Exhaust
Obstructed Return Air
Obstructed Duct(s) OR lack of proper number/size of ducts

Weak Hi Temp Limit Switch?
*AFM models use a 190*F Limit Switch

How many ducts do you have?
What size are they....4" or 2" ?
Where on furnace are they installed?
How is furnace installed.......horizontally OR Vertically?

flbill · 01-03-2023, 03:13 PM

Quote:

Originally Posted by Old-Biscuit

Fan stays running indicates Hi Temp Limit Switch is OPENING vs bad circuit board

Turning Thermostat Off/Back On and furnace working ----- restarts furnace sequence (Fan staying running allows for Hi Temp Limit to Cool off & close so normal startup sequence can occur)

**When it trips/fan stays running..........if you wait does furnace start backup or does fan shut off after 5 minutes?

--> After heat turns off, fan runs then shuts down. Based on the 3 flashes (soft lockout) it MAY restart after an hour - honestly do not know.

Why is Hi Temp Limit Switch opening/heat exchanger overheating?
Airflow........
Low DC Voltage...fan motor not coming up to full speed (enough to close sail switch but not enough airflow to remove heat)

--> I did not check the voltage, but batteries are new and generator has been on each time. Fan is turning with no broken vanes and seems balanced.

Obstructed Intake/Exhaust
--> Checked. No obstructions.

Obstructed Return Air
--> Checked. No.

Obstructed Duct(s) OR lack of proper number/size of ducts
--> see below.....

Weak Hi Temp Limit Switch?
*AFM models use a 190*F Limit Switch

How many ducts do you have?
--> 6
What size are they....4" or 2" ?
--> 4" and two 2"

Where on furnace are they installed?
--> They are NOT installed according to the schematic I have from Thor. 2 small ones should be on the back, they are on sides. and two 4" are on the top, and Thor shows none there.

How is furnace installed.......horizontally OR Vertically?

--> Horizontally.

TODAYS WORK:
- Disconnected 4 of the hoses (2 2", 2 4").
- SLOWLY opened propane.
- Turned on all power and fired up generator
- Removed outside access panel and left exhaust vent in place
- Fired up stove and fridge.
- Fired up furnace and it ran over 10 minutes. I manually shut it down as it was really hot in unit! Thought - wow, thats it! Air flow...

- Rerouted best I could. Reconnected hoses. Re-fired furnace. Shut down after about 6 minutes.

- Reset, removed two hoses. Re-fired furnace. Shut down after about 6 minutes.

- Stopped for the day.

I don't know at this point if the initial run with disconnected hoses was a fluke, or a real fix...
Should I redo all hoses according to schematic?
Personally - I suspect the high temp switch is opening - but could that be as simple as hoses in the wrong places?

One thing I did notice when checking the sail switch (removed and cleaned). It is basically flat, but the drawing for it here shows it with a clear angle to it.

I am willing to bed it if that is something I should do.

Old-Biscuit · 01-03-2023, 04:46 PM

Early models of the AF series used a Flat Paddle and changed to the Bent Paddle Sail Switch sometime later production runs. No clear time frame or S/N

Sail Switch not closing.....no Ignition would occur
Sail Switch closing/opening (fluttering) would cause loss of flame then flame then loss of flame etc
Changing to the Bent paddle would not be unwarranted as it would eliminate an issue (reason flat to bent occurred)

Duct work ----THREE 4" minimum required
2" can be used but has to be TWO 2" to equal ONE 4"
SO you have the correct number of ducts/36 sq in

BUT....they are in WRONG places

--> They are NOT installed according to the schematic I have from Thor. 2 small ones should be on the back, they are on sides. and two 4" are on the top, and Thor shows none there.

4" should be on sides (rear duct openings)
2" should be on rear

None on top......
extra 2" or 4" could be added

Think you overheating issue is directly related to the duct work

Statement in manual
*Note the table is for minimum requirements and should in most
cases allow the unit to operate correctly. If the burner cycles on
and off on the high temperature limit. Extra ducting can be used
to help correct this condition due to restriction or bends in duct
work