Heater Fan wont cycle off

[dianna119]

We've been working well for a while but now have a new issue. We replaced the Thermostat a few years ago and all was well. Last winter (1 year ago) I had an issue when the propane heat was on occasionally the fan (set to auto) would try to cycle off when set temp was reached in coach. It actually tries to go off and pops right back on. In summer the basement AC worked fine and the fan cycled off properly. Now here we are in winter again and the fan when set to heat tries to cycle off and jumps back on. I ended up turning it completely off and after turning on/off 3-5 times finally the fan stayed off. I plugged in an electric heater but waking up to 40 degrees inside the rv wasn't fun. Ideas? What is confusing is the fan cycles properly when in AC mode. Can it be the thermostat or something else? Thanks for your input and Merry Christmas.

[dougrainer]

YC 1 wrote:

dougrainer wrote:

YC 1 wrote:
I am betting low voltage at the fan is causing the vane switch to not allow the ignition sequence to start.

Time to check the voltage with the fan running right at the heater wires.

Of course a quick battery check would be in order to start.

The OP is NOT having a Lighting problem. They are having a fan NOT shutting OFF after a Heating cycle is complete. Doug

". I can hear the furnace burner shutting down and fan stays on."

If the voltage recovers enough for it to light and come up to temp the voltage could be pulled down enough for the fan to slow and not allow the furnace to light again. I have seen this happen and you end up with a dead battery and cold rv.

Low voltage is easy enough to check for.

While this is true, the OP would be DEAD overnight and would complain of no lighting or other 12 volt problems. Doug

[YC_1]

dougrainer wrote:

YC 1 wrote:
I am betting low voltage at the fan is causing the vane switch to not allow the ignition sequence to start.

Time to check the voltage with the fan running right at the heater wires.

Of course a quick battery check would be in order to start.

The OP is NOT having a Lighting problem. They are having a fan NOT shutting OFF after a Heating cycle is complete. Doug

". I can hear the furnace burner shutting down and fan stays on."

If the voltage recovers enough for it to light and come up to temp the voltage could be pulled down enough for the fan to slow and not allow the furnace to light again. I have seen this happen and you end up with a dead battery and cold rv.

Low voltage is easy enough to check for.

[jeeperdude10]

Just a thought.....has it been raining? Have you washed the RV recently? The reason I am asking is that our furnace fan would come on without it even being set/turned on after a heavy rain. We have the Atwood furnace that works with the front a/c thermostat. Anyway, after removing the outside facia, I put some peel em stick em 1/4 inch foam insulation (roll type) over the indents on the foam gasket and no more problem. May be really off base, but just wanted to share, in case a possible 'fix'.

[dougrainer]

filrupmark wrote:
Out of propane ? Never reaching set temperature and fan keeps running.

They are not having a heating problem. ONLY the fan will not shut off after a correct heating cycle. If the Furnace runs out of LP the fan will shut down. Doug

[dougrainer]

YC 1 wrote:
I am betting low voltage at the fan is causing the vane switch to not allow the ignition sequence to start.

Time to check the voltage with the fan running right at the heater wires.

Of course a quick battery check would be in order to start.

The OP is NOT having a Lighting problem. They are having a fan NOT shutting OFF after a Heating cycle is complete. Doug

[dougrainer]

doxiemom11 wrote:
Our fan shuts off just a couple minutes after burner shuts down after the set temp has been reached. It has never even run as long as 5 minutes.

Your Hi temp switch functions correctly. The OP's does not. Doug

[YC_1]

I am betting low voltage at the fan is causing the vane switch to not allow the ignition sequence to start.

Time to check the voltage with the fan running right at the heater wires.

Of course a quick battery check would be in order to start.

[doxiemom11]

Our fan shuts off just a couple minutes after burner shuts down after the set temp has been reached. It has never even run as long as 5 minutes.

[filrupmark]

Out of propane ? Never reaching set temperature and fan keeps running.

[dougrainer]

dianna119 wrote:
Thanks Doug, makes sense. I can hear the furnace burner shutting down and fan stays on. I have left it on for upwards of an hour thinking it should shut off and just blows cold air making the inside cold again and then burner comes on. In previous years, the fan would shut down after about 2-3 minutes. DiAnna

just saw your ps, Yes, the thermostat was replaced same brand/type as original,

Odds are the Hi temp control tstat of the furnace is BAD. It is NOT opening the tstat when the furnace has cooled down to shut off. It is a Bi-Metal disc and after years of use is probably just worn out. It needs replaced. Doug

[dianna119]

Thanks Doug, makes sense. I can hear the furnace burner shutting down and fan stays on. I have left it on for upwards of an hour thinking it should shut off and just blows cold air making the inside cold again and then burner comes on. In previous years, the fan would shut down after about 2-3 minutes. DiAnna

just saw your ps, Yes, the thermostat was replaced same brand/type as original,

[dougrainer]

1. The LP Furnace has NOTHING to do with the operation of your Basement AC system and fan.
2. The Basement AC and ITS Fan is separate from the LP furnace and ITS fan
3. The LP furnace, really need to know the Brand and Model of it.
4. The LP furnace just responds to a 12 volt signal from the wall tstat. Once that signal is received, the LP furnace and burner and Fan are all controlled by the furnace NOT the tstat. You cannot run the LP furnace fan by itself, like the Basement AC system.
5. Tstat sends signal. Furnace fan comes ON. after 20 seconds the Burner lights and the furnace heats the RV. When the RV reaches set temp, the Furnace burner shuts OFF and then the Furnace Fan will continue running until the Burner chamber cools down and then it shuts OFF. Can take from 5 minutes to 15 minutes depending on how hot the chamber is. IF the wall tstat calls for Heat BEFORE the cool down cycle is complete the furnace will relight the burner and start heating again. Doug

PS, The Basement AC and fan are 120 volt operated. The Furnace and its fan are 12 volt operated.
Also, did you replace the wall tstat with the original brand and model tstat?

[Mandalay_Parr]

On mine, there is a board on the front AC that controls all functions. Also the furnace controls the fan.