Furnace not staying on

[2hams]

You should be able to find the part numbers if you know your furnace model number. We think the model number was in our paperwork, but Dave confirmed it by looking at the furnace. In our 2014 303 (which Rob aptly named the classic), we have an Atwood 8535-IV. The limit switch is 37022. The sail switch is 36680. I will post the pictures and the disassembly (ahhhh access) instructions with a discussion of what Dave did in a separate thread.


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[Rich T]

Obviously these part#s are going to vary depending on the brand and model of the furnace as you point out Dave. My 2016 300GK has a Suburban Model SF-35Q. The part # for the sail switch is 73-0528, high limit 79-8538. I'm not sure if these are Suburban part #s or just #s assigned by my suppler? Still hopin they will be spare parts.

Looking forward to seeing your pics Dave.
Rich

[orbiker]

How far does your system get in this chart?

Time Line
Description - Sequence of Events
StartThermostat Callsfor HeatThe wall thermostat controls the operation of the furnace by reacting to roomtemperature, this allows current to flow through the On/Off switch to the module board.The module board constantly checks for a minimum 9.5 volts. If there is not 9.5 volts,the module board will go into a stand by mode until adequate power is supplied. It willthen resume normal operation.Upon a call from the thermostat, the module board thermostat circuit will go active. Thesail switch circuit is verified as being open. The blower output is energized. Blower motor starts.15 Seconds PurgeCycleThe module board will then verify that the sail switch circuit is closed and motor is upto speed. If this circuit remains open for 30 seconds after the blower motor starts, themodule board will go into lock out and shut down the blower motor.The module board checks that the gas valve relay contacts (which are located on themodule board) are open before the ignition sequence starts.The board has a pre-purge timing circuit of (approximately 15 seconds). This allows thechamber to purge.7 Seconds IgnitionCycle and FlameSenseThe module board will energize the gas valve and enable the high voltage spark outputto the electrode for 7 seconds of ignition time.The module board will then check for flame sense to verify successful lighting of themain burner flame. Sparking will then be terminated and the gas valve and blower outputs will remain energized. If ignition is successful the module board will monitor the flame sense, sail switch andlimit switch circuits, and the thermostat inputs during the heating period.The flame is sensed through the spark wire and electrode. Therefore, it is essential thatthe electrode is properly positioned in the burner flame.2 and 3 Ignition
ndrd
Cycles if Required3 Try Ignition BoardIf the flame is not sensed after seven (7) seconds, a second 15 second purge cycle willbegin followed by a second Trial-For-Ignition sequence. After three (3) Trial-For-Ignitionattempts with no ignition of the main burner, the module board will de-energize the gasvalve immediately and blower will run for 3 minutes and then shutdown in lockout.Heating CycleIf during the heating cycle, the limit switch circuit opens and remains open for 5minutes, the module board will go into lock out and shut down the blower motor. If thisoccurs, the thermostat will need to be reset for the furnace to operate.90 Second ShutDownWhen the thermostat has reached its set point and the demand for heat ends, the gasvalve will be de-energized and the flame will go out. The post purge period of 90seconds begins. When it times out, the blower motor output is removed, and the blower stops.


25
Sequence of Operation for 24 VAC Fan Control Module Board
Part Number 520947
Time Line
Description - Sequence of Events
StartThermostat Callsfor HeatThe wall thermostat controls the operation of the furnace by reacting to roomtemperature, this allows current to flow through the On/Off switch to the module board.The module board must have a minimum 18 volts for normal operation.Upon a call from the thermostat, the module board thermostat circuit will go active. Thesail switch circuit is verified as being open. The blower output is energized. Blower motor starts.15 Seconds PurgeCycleThe module board will then verify that the sail switch circuit is closed and motor is upto speed. If this circuit remains open blower motor will run continuously until sail switchcloses.The module board checks that the gas valve relay contacts (which are located on themodule board) are open before the ignition sequence starts.The board has a pre-purge timing circuit of (approximately 15 seconds). This allows thechamber to purge.7 Seconds IgnitionCycle and FlameSenseThe module board will energize the gas valve and enable the high voltage spark outputto the electrode for 7 seconds of ignition time.The module board will then check for flame sense to verify successful lighting of themain burner flame. Sparking will then be terminated and the gas valve and blower outputs will remain energized. If ignition is successful the module board will monitor the flame sense, sail switch andlimit switch circuits, and the thermostat inputs during the heating period.The flame is sensed through the flame sence electrode. Therefore, it is essential thatthe electrode is properly positioned in the burner flame.2 and 3 Ignition
ndrd
Cycles if Required3 Try Ignition BoardIf the flame is not sensed after seven (7) seconds, a second 15 second purge cycle willbegin followed by a second Trial-For-Ignition sequence. After three (3) Trial-For-Ignitionattempts with no ignition of the main burner, the module board will de-energize the gasvalve immediately and blower will run for 90 seconds and then shutdown in lockout.Heating CycleIf during the heating cycle, the limit switch circuit opens and remains open the gas valvewill close and the blower motor will continue to run.90 Second ShutDownWhen the thermostat has reached its set point and the demand for heat ends, the gasvalve will be de-energized and the flame will go out. The post purge period of 90seconds begins. When it times out, the blower motor output is removed, and the blower stops.


26
Sequence of Operations for SHD-25421st Stage Call for Heat
The wall thermostat controls the operation of the dual stage furnace by reacting to room temperature. This allows current toflow through the On/Off switch to the Blower Speed Control Board then to the Module Board.The module board constantly checks for a minimum 9.5 volts. If there is not 9.5 volts, the module board will go into a standbymode until adequate power is supplied. It will then resume normal operation.Upon a call from the thermostat the first stage will be activated. The module board thermostat circuit will go active and the sailswitch is verified as being open. The blower output is energized. The blower motor starts.
15 Second Purge Cycle
The module board will then verify that the sail switch circuit is closed and motor is up to speed. If this circuit remains open for 30 seconds after the blower motor starts, the module board will go into lockout and shut down the blower motor.The module board checks that the gas valve relay contacts (located on the module board) are open before the ignitingsequence starts.The board has a pre-purge timing circuit of approximately 15 seconds. This allows the combustion chamber to purge.7 Second Ignition Cycle and Flame SenseThe module board will energize the gas valve and enable the high voltage spark output to the electrode for a seven secondignition period.The module board will then check for flame sense to verify successful lighting of the main burner flame. Sparking of the igniter is then terminated. The gas valve and blower outputs will remain energized.If ignition is successful the module board will monitor the flame sense, sail switch, and the limit switch circuits. The flame issensed through the spark wire and electrode therefore, it is essential that the electrode is properly positioned in the burner flame.
3 try Ignition Board
If the flame is NOT sensed after seven (7) seconds, or if the unit fails to ignite, a second fifteen (15) purge cycle will beginfollowed by second trial for ignition sequence. After three (3) trial for ignition attempts with no ignition of the main burner, themodule board will de-energize the gas valve immediately and the blower will run for three (3) minutes and then go into lockoutmode.
2 Stage Heating
nd
If during the thermostat cycle the demand for heat drops below the second stage thermostat setting ( 3 to 5 degrees variancedepending on thermostat manufacturer), the blower speed control board will be energized. The blower speed control boardwill energize the additional gas valve solenoid and increase motor speed to the high position. Furnace will remain in the secondstage operation until thermostat is satisfied.
90 Second Shut Down
When the thermostat has reached its set point and the demand for heat ends, the gas valve will be de-energized and the flamewill go out. The post combustion purge period of 90 seconds begins. When it times out, the blower motor output is removed,and the blower stops.

[orbiker]

HERE is a manual for Suburban. Go to troubleshooting Pg 27

[Rich T]

Orbiker
Thanks, a lot of that is over my head but the pg 27 trouble shooting guide is great. I may have jumped the gun ordering parts. The last 2 times I operated the furnace it worked fine. I'm going to continue testing it to try and replicate the original malfunction and go from there. Thanks again for the detailed reply.
Rich

[blckgnx]

WOW!! Sure wish I had found this sooner. I'm working on wife's 2017 377mbs and having exactly same problem, although have already spent way too much time and money on it.(too long of a story). FYI: On the 377, I pulled the outer panel, One screw securing the heater unit, the propane connection on the left side, and was able to pull the unit straight out. (about 15min) the outer case with all the duct hoses stays right where it is. OK, I've replaced control board with an American one, and the "limit swtch". Still having the same problem. Called wife, and she said it worked perfect this morning, may not tomorrow! I'll post my progress and keep in touch. Thanks all, what a great Forum!!!!!!! Ron

[Rich T]

WOW!! Sure wish I had found this sooner. I'm working on wife's 2017 377mbs and having exactly same problem, although have already spent way too much time and money on it.(too long of a story). FYI: On the 377, I pulled the outer panel, One screw securing the heater unit, the propane connection on the left side, and was able to pull the unit straight out. (about 15min) the outer case with all the duct hoses stays right where it is. OK, I've replaced control board with an American one, and the "limit swtch". Still having the same problem. Called wife, and she said it worked perfect this morning, may not tomorrow! I'll post my progress and keep in touch. Thanks all, what a great Forum!!!!!!! Ron

Ron
I have continued to check my furnace and so far it is still working ok. Hopefully it will keep working and yours as well. I wish you the best with yours.
Rich

[orbiker]

Sometimes it's just a loose connection and you touched it to help it connect a bit better.

[blckgnx]

Good morning Richard, I've been here "many" times before, so I don't have my hopes up. It will work sometimes as long as a week, then go right back to acting up. Good luck on yours too. I'll continue, and post here when I get it solved. Again, have a great blessed day. Ron

Ron
I have continued to check my furnace and so far it is still working ok. Hopefully it will keep working and yours as well. I wish you the best with yours.
Rich

[blckgnx]

UPDATE! 11-26117 A few days ago, I checked the regulator to find the 90 deg fitting had been installed, so bought a new reg and installed. Unit worked great for almost a week. This morning she called and the furnace ran for almost 30min then quit. She started it back up manually and it only ran for a few min and quit again. Ambient temp is high 40's, and the burners on the stove all work fine?? Had her switch over to the curb side bottle, and no difference?? The other day when I replaced the reg I noticed that there is a small regulator on the hose going to the cross over reg on the street side? It is "red" and does not have any adjustments on it??? Still open to ideas????? Thanks ahead of time. Ron