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Old 09-26-2022, 08:24 PM   #1
cstewart
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M.O.C. #30722
Furnace not starting

I have a 2019 Montana 3791RD. The furnace is not producing heat. I turn the thermostat up the fan come on for a minute and shuts off. It seems it is not clicking to ignite the fuel so it shuts off. The fuel tanks are full.

I am looking for info on what the problem is and how to get to the unit to make the repair. The unit is new to me so I am not sure and donít want to break it.

I am thinking it could be the control board since the fuses are not blown. I donít know how to access the unit.
 
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Old 09-26-2022, 08:28 PM   #2
Daryles
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Blower coming on then shutting off is classic sail switch symptoms.
There is a Suburban furnace manual in the files section.
I would start by removing and cleaning the sail switch. Followed by slightly bending it to catch more air. Repeat as necessary or until you figure out its totally bad and needs replaced.
A multimeter would be a big help while troubleshooting.
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Old 09-26-2022, 10:04 PM   #3
Carl n Susan
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Here is a description of the operation of the Atwood furnace (I am pretty sure you have it and not a Suburban). This comes from Page 30 of the PDF "Atwood Furnace Training Manual". It can be found in the Files section or via this link. https://www.montanaowners.com/forums...?do=file&id=54

You probably are better off downloading the entire PDF. Note: There is a flashing LED inside that indicates the reason for the non-start.

================================

The ON/OFF switch allows power to pass to the circuit breaker
and the thermostat.

The thermostat controls the operating circuit to the furnace by
reacting to room temperature. When room temperature is below
the thermostat set point, the contact closes to allow current to flow
to the relay (relay can be either external or part of the ignition
control board).

The circuit breaker limits amperage draw of motor.

The relay allow current to pass to the motor by closing a switch
within the relay. Voltage from the thermostat activates the relay to
turn the fan on. This takes 1-25 seconds (on units with relay on
the ignition control board there is only a 1-2 second delay).

Current flows to the motor to operate the blower. One end of the
motor shaft is for the circulating air wheel and the other side is for
the combustion air wheel.

Circulating air blows against the sail switch and closes the
contacts, completing the circuit. The sail switch is a safety device
that insures air flow before ignition.

The limit switch is a safety device that protects the furnace from
overheating. The contacts in the limit switch open at a given
temperature setting, shutting off power to the electronic ignition
system that controls the gas valve.

As power is applied to the circuit board, the system closes the
following:
1. A timing circuit allows the blower to purge the chamber
(15-17 seconds).
2. The board supplies current to the gas valve and causes
it to open.
3. As the valve opens, the board sends a high voltage
spark to the electrode at the burner. The board detects
the presence of a flame. If the flame is not sensed after
approximately six seconds, the board will lock out (after
three tries for ignition, the control will lockout for one
hour unless power is removed or thermostat is
cycled).shutting off power will restart the cycle.
4. If the system does not ignite and the thermostat
remains closed, the blower will remain on until the
thermostat is reset manually on units with an external
relay (units with the relay on the ignition control will
shut the blower off even if the thermostat contacts
remain closed). If the thermostat is has not be satisfied
within one hour the system will try the ignition cycle
again.

When the thermostat senses the desired room air temperature
contact open, removing power from the ignition system and
shutting off the gas valve. The blower runs until the relay opens
(90 seconds) the circuit shutting off current to the motor.
On newer control a diagnostic error code light has been added by
counting the flashes an error code can be determined. See
diagnostic information for code failures.



Number of Flashes Diagnostic Information
1 w/ 3 sec. pause - Air Flow / Limit Fault
2 w/ 3 sec. pause - Flame Sense Fault
3 w/ 3 sec. pause - Ignition Lockout Fault
Steady ON no Flashing - Internal Control Failure
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Old 09-26-2022, 10:11 PM   #4
wed
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Check are you getting propane to the stove ? Like other have said clean and see if you smell gas at the furnace
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Old 09-27-2022, 06:14 AM   #5
cstewart
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M.O.C. #30722
Thank you this is very helpful. Where do I access the sail switch? I have a black panel on the outside that has the exhaust, do I take that panel off of is there another location.


Quote:
Originally Posted by Carl n Susan View Post
Here is a description of the operation of the Atwood furnace (I am pretty sure you have it and not a Suburban). This comes from Page 30 of the PDF "Atwood Furnace Training Manual". It can be found in the Files section or via this link. https://www.montanaowners.com/forums...?do=file&id=54

You probably are better off downloading the entire PDF. Note: There is a flashing LED inside that indicates the reason for the non-start.

================================

The ON/OFF switch allows power to pass to the circuit breaker
and the thermostat.

The thermostat controls the operating circuit to the furnace by
reacting to room temperature. When room temperature is below
the thermostat set point, the contact closes to allow current to flow
to the relay (relay can be either external or part of the ignition
control board).

The circuit breaker limits amperage draw of motor.

The relay allow current to pass to the motor by closing a switch
within the relay. Voltage from the thermostat activates the relay to
turn the fan on. This takes 1-25 seconds (on units with relay on
the ignition control board there is only a 1-2 second delay).

Current flows to the motor to operate the blower. One end of the
motor shaft is for the circulating air wheel and the other side is for
the combustion air wheel.

Circulating air blows against the sail switch and closes the
contacts, completing the circuit. The sail switch is a safety device
that insures air flow before ignition.

The limit switch is a safety device that protects the furnace from
overheating. The contacts in the limit switch open at a given
temperature setting, shutting off power to the electronic ignition
system that controls the gas valve.

As power is applied to the circuit board, the system closes the
following:
1. A timing circuit allows the blower to purge the chamber
(15-17 seconds).
2. The board supplies current to the gas valve and causes
it to open.
3. As the valve opens, the board sends a high voltage
spark to the electrode at the burner. The board detects
the presence of a flame. If the flame is not sensed after
approximately six seconds, the board will lock out (after
three tries for ignition, the control will lockout for one
hour unless power is removed or thermostat is
cycled).shutting off power will restart the cycle.
4. If the system does not ignite and the thermostat
remains closed, the blower will remain on until the
thermostat is reset manually on units with an external
relay (units with the relay on the ignition control will
shut the blower off even if the thermostat contacts
remain closed). If the thermostat is has not be satisfied
within one hour the system will try the ignition cycle
again.

When the thermostat senses the desired room air temperature
contact open, removing power from the ignition system and
shutting off the gas valve. The blower runs until the relay opens
(90 seconds) the circuit shutting off current to the motor.
On newer control a diagnostic error code light has been added by
counting the flashes an error code can be determined. See
diagnostic information for code failures.



Number of Flashes Diagnostic Information
1 w/ 3 sec. pause - Air Flow / Limit Fault
2 w/ 3 sec. pause - Flame Sense Fault
3 w/ 3 sec. pause - Ignition Lockout Fault
Steady ON no Flashing - Internal Control Failure
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Old 09-27-2022, 07:37 AM   #6
ChuckS
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M.O.C. #20949
Since you are blessed wit( an outside access panel gaining acccess to the control board, sail switch, blower motor, etc is easy.. take that black outer panel cover off

Sail switch is held in b6 two screws, remove it and test with a multimeter while moving paddle arm back and forth to verify continuity

Also.. folks sa6 clean the sail switch.

All you can clean is the area around the arm of the switch..you can’t clean anything else unless you drill out the rivets to gain access to the contacts inside.

Spraying compressed air or any liquid contact cleaner is a joke at best.. IMO

Watch my video showing a typical Saul switch being taken apart and why spraying contact cleaner etc will just cause more issues

https://youtu.be/Neg5E0WemgY
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Old 09-27-2022, 08:45 AM   #7
DutchmenSport
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M.O.C. #22835
Agree, your issue is with the sail switch. Here's another video where the problem is the sale switch, maybe something just this simple is what's wrong with yours. Start simple, move out from there.

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Old 09-27-2022, 09:06 AM   #8
jsb5717
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With exterior access the sail switch is one of the easiest things to check and clean or replace. It's usually just a little lint caught between the contacts. Unscrew and pull the switch out of the air chamber, clean it, and reinstall. Check it with a meter for continuity to make sure it's working. If not replace it.

If the furnace still doesn't attempt to ignite then then you will need to go deeper into it by checking the plug contacts on the main board or actually replacing the main board.

Chances are good that it's just the sail switch.
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Old 10-05-2022, 04:13 PM   #9
Dee_Dub
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Your propane regulator could be defective. A simple test is to lite a burner on your stove and notice the height of the flame. Turn on a second burner watching the first burners flame height. If the first flame drops when the second one starts up you may have a defective propane regulator.
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Old 10-06-2022, 07:11 AM   #10
cstewart
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M.O.C. #30722
Thank you

This information was very helpful! Very easy access with the black panel. The sail switch was clean. All I needed to do is reset the switch. No sure why it tripped.
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Old 10-06-2022, 09:57 PM   #11
twindman
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Which switch is this? Is there something on the sail switch?
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Old 10-07-2022, 01:13 AM   #12
jsb5717
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I'm sure he's talking about the power switch next to the main board. It's like an on/off switch except it says reset/off. That switch will trip to Off when it fails to light 3 times.
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Old 10-07-2022, 09:50 AM   #13
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Do all furnaces have this external switch? I never had it happen, but I don't think I have actually taken the cover off the outside and looked around. Does it reset itself so you can try later, or is that the issue here and it just stayed off?
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Old 10-07-2022, 11:03 AM   #14
jsb5717
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I don't know if all furnaces have them. Likely all of the newer Atwoods do. If your furnace fails to light and the switch trips you'll need to remove the exterior cover and reset it manually. There is likely something else going on that is preventing it from working so you'll need to get in there anyway to troubleshoot.
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