Furnace Fan won't turn off, 2004 Alpha 40'

[WildeOne]

I am a new motorhome owner (8/2016). My furnace's blower would not turn off with the thermostat (blowing air, no heat) so I accessed the main switch through the outside panel to turn it off.

Is there a filter somewhere that could be clogged and causing the safety relay to turn off the heat and keep the fan blowing? I've poured over the book and opened every panel I can find and am confounded.

Thanks for any input.

[dougrainer]

DrivingMissDaisy wrote:

dougrainer wrote:

DrivingMissDaisy wrote:
Your heater has entered "lock out" mode. this happens when during the start sequence, a flame is not established in 7 seconds. The blower will run until the thermostat is cycled off. Most common cause is flame sensor, try cleaning and adjusting first, then replace if necessary, it is not an expensive part.

True for OLDER furnaces. Depending on his year and model furnace, he probably has the current control board that shuts the Fan OFF when the flame sequence fails. The models that have this have the Fan relay ON the Ignition module. Doug

Ok, then it looks like it would be a faulty control board, probably a stuck relay. The only other thing that would run fan continuously would be a faulty on/auto fan switch in the thermostat and that's a long shot, I've never heard of that happening.

As I stated previously, NO wall tstat can control the furnace blower motor. Auto or ON. That feature is for the AC system ONLY. Doug

[gatorcq]

This is a standard Atwood Furnace.
With Blower on, wait, ignition, flame sensor
There is no on/off switch with this furnace, except for the circuit breaker next to the blower motor.

Furnace Model 8940_DLP_III

Finally, since you are the proud owner of an Alfa Please sign up for these 2 groups. April 2017 we will be having out anual Alfa Chapter Rally. This years rally will be in Tucson. Normally over 100 rigs gather.

Now on the sad side this person "Wildeone" Has not come back to this post.

https://groups.yahoo.com/neo/groups/alfaseeya/info

https://groups.yahoo.com/neo/groups/SeeYaDP/info

[DrivingMissDais]

dougrainer wrote:

DrivingMissDaisy wrote:
Your heater has entered "lock out" mode. this happens when during the start sequence, a flame is not established in 7 seconds. The blower will run until the thermostat is cycled off. Most common cause is flame sensor, try cleaning and adjusting first, then replace if necessary, it is not an expensive part.

True for OLDER furnaces. Depending on his year and model furnace, he probably has the current control board that shuts the Fan OFF when the flame sequence fails. The models that have this have the Fan relay ON the Ignition module. Doug

Ok, then it looks like it would be a faulty control board, probably a stuck relay. The only other thing that would run fan continuously would be a faulty on/auto fan switch in the thermostat and that's a long shot, I've never heard of that happening.

[dougrainer]

DrivingMissDaisy wrote:
Your heater has entered "lock out" mode. this happens when during the start sequence, a flame is not established in 7 seconds. The blower will run until the thermostat is cycled off. Most common cause is flame sensor, try cleaning and adjusting first, then replace if necessary, it is not an expensive part.

True for OLDER furnaces. Depending on his year and model furnace, he probably has the current control board that shuts the Fan OFF when the flame sequence fails. The models that have this have the Fan relay ON the Ignition module. Doug

[DrivingMissDais]

Your heater has entered "lock out" mode. this happens when during the start sequence, a flame is not established in 7 seconds. The blower will run until the thermostat is cycled off. Most common cause is flame sensor, try cleaning and adjusting first, then replace if necessary, it is not an expensive part.

[Clay_L]

If the high temp cut-off thermodisc switch fails, what you are describing happens. Not the only cause for what you describe and not common but does happen.

[dougrainer]

tropical36 wrote:

WildeOne wrote:
I am a new motorhome owner (8/2016). My furnace's blower would not turn off with the thermostat (blowing air, no heat) so I accessed the main switch through the outside panel to turn it off.

Is there a filter somewhere that could be clogged and causing the safety relay to turn off the heat and keep the fan blowing? I've poured over the book and opened every panel I can find and am confounded.

Thanks for any input.

Other than having your thermo setting for fan on, were you plugged in and/or were your batteries fully charged?
If in auto then it sounds like the sail sw. shut off the gas from lack of proper air flow and in which case the temp. setting couldn't be satisfied.
Hence a continuous run until the batteries are depleted completely.

Except for one very rare Atwood model(usually used on very hi end 5th wheels and park Models and HAS to use the specific Atwood wall tstat) NO furnace blower reacts to the Wall tstat Auto/ON fan switch. The Fan is controlled by the furnace internal controls and will ALWAYS Shut ON and OFF when the heat cycle is complete unless it malfunctions. Doug

[tropical36]

WildeOne wrote:
I am a new motorhome owner (8/2016). My furnace's blower would not turn off with the thermostat (blowing air, no heat) so I accessed the main switch through the outside panel to turn it off.

Is there a filter somewhere that could be clogged and causing the safety relay to turn off the heat and keep the fan blowing? I've poured over the book and opened every panel I can find and am confounded.

Thanks for any input.

Other than having your thermo setting for fan on, were you plugged in and/or were your batteries fully charged?
If in auto then it sounds like the sail sw. shut off the gas from lack of proper air flow and in which case the temp. setting couldn't be satisfied.
Hence a continuous run until the batteries are depleted completely.

[Sloop_Smitten]

Older furnaces have a time delay relay which sends voltage to the fan. If that goes bad it can cause your fan to run continuously or not at all. On newer furnaces the fan is controlled by a circuit board. We need to know the furnace model and number to provide accurate guidance.

[crasster]

zigzagrv wrote:
The furnace fan will run after the heat shuts of for a few minutes till everything (ducts and heater itself) cools down. This is normal.

The switch mentioned above only controls the A/C fan I believe.

If the heater has lights it should light the "purge" cycle for this - if this is what is happening.

[zigzagrv]

The furnace fan will run after the heat shuts of for a few minutes till everything (ducts and heater itself) cools down. This is normal.

The switch mentioned above only controls the A/C fan I believe.

[Dick_B]

Could it be that simple as the On/Auto switch position? Let's hope so.

[jplante4]

Usually there's a switch on the thermostat that says "Fan On/Auto". In Auto, the fan runs with the furnace. In On, the fan runs all the time.