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Old 05-24-2012, 08:24 PM   #1
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Thermostat turns on Furnace & AC fan

Last weekend I ran the furnace while the trailer was running on battery power only. No problem.

Then one morning I connected the shore power to my generator, and set the thermostat once again to heat. The furnace came on as it should, but also the AC fan. Why would this happen? I flipped the breaker for the AC to keep the AC fan off. The furnace worked normally.

I don't often run the furnace as we use electric heaters. But I swear this never happened last year.
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Old 05-24-2012, 09:13 PM   #2
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Sounds like something fishy with the thermostat. What thermostat do you have in your trailer?
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Old 05-24-2012, 09:25 PM   #3
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Last weekend I ran the furnace while the trailer was running on battery power only. No problem.

Then one morning I connected the shore power to my generator, and set the thermostat once again to heat. The furnace came on as it should, but also the AC fan. Why would this happen? I flipped the breaker for the AC to keep the AC fan off. The furnace worked normally.

I don't often run the furnace as we use electric heaters. But I swear this never happened last year.
Check to make sure the thermostat fan switch is on Auto and not On
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Old 05-24-2012, 09:33 PM   #4
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sounds like the thermostat is faulty or wired wrong to me. if it otherwise controls, i would check to see if it is wired right or none of the bare parts of the wire are touching terminals that they aren't supposed to.

only other possibility would be if u have a heat pump with furnace backup. even with that, i don't see both of them coming on on initial start up.
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Old 05-24-2012, 09:38 PM   #5
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If the fan switch in the thermostat is in the On position, it will run as soon as 110v is available which is why it didn't run until he hooked his gen to the power cord. The fan switch has to be in the Auto position for it to only work when the AC is on.
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Old 05-24-2012, 09:49 PM   #6
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Originally Posted by dunnnc View Post
If the fan switch in the thermostat is in the On position, it will run as soon as 110v is available which is why it didn't run until he hooked his gen to the power cord. The fan switch has to be in the Auto position for it to only work when the AC is on.
i have an older thermostat; my A/C fan doesn't operate when i switch to heat
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Old 05-25-2012, 01:32 AM   #7
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Thanks. I'll go out and check tomorrow and report if I figure it out.
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Old 05-25-2012, 09:23 AM   #8
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Do you have the Dometic Digital thermostat?


If so, then I agree with what dunnnc had to say.

Here's some info that might help you.

Use the On/Off Mode button to select FAN. Then use the +/- button to select either Hi, Lo or Auto.
When using the AC and the fan is in the Hi or Lo setting it will run continuously while the compressor will cycle on and off.
In the Auto mode the fan will cycle on and off as well.

If the fan is set on Hi or Lo while using the furnace the AC fan will run continuously, so be sure to set the fan on Auto when using the furnace.
You can, however, leave the AC fan running while using the furnace to help with condensation problems.

After setting the fan, Use the On/Off Mode button to select COOL for AC use. Use the +/- button to select the thermostat temperature setting.
Use the same procedures for the Furnace.

When using the AC, in the Auto mode the fan will run on high when the room temperature is 5 or higher than the thermostat setting. When the room temperature drops to within 4 or less than the thermostat setting, the fan will stop for a few seconds the start again in the Lo mode.

Hope this helps.
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Old 05-25-2012, 09:42 AM   #9
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I second dunnnc's suggestion. I had the same "problem" and it turned out I just needed to figure out that the fan control and the furnace/AC were 2 different settings in the thermostat. I have a 2011 Surveyor SP260.
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Old 05-25-2012, 09:44 AM   #10
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Here is a picture of our Coleman-Mach thermostat with the Auto-On fan switch.
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Old 05-25-2012, 11:50 AM   #11
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Quote:
Originally Posted by grhodes50 View Post
Do you have the Dometic Digital thermostat?


If so, then I agree with what dunnnc had to say.

Here's some info that might help you.

Use the On/Off Mode button to select FAN. Then use the +/- button to select either Hi, Lo or Auto.
When using the AC and the fan is in the Hi or Lo setting it will run continuously while the compressor will cycle on and off.
In the Auto mode the fan will cycle on and off as well.

If the fan is set on Hi or Lo while using the furnace the AC fan will run continuously, so be sure to set the fan on Auto when using the furnace.
You can, however, leave the AC fan running while using the furnace to help with condensation problems.

After setting the fan, Use the On/Off Mode button to select COOL for AC use. Use the +/- button to select the thermostat temperature setting.
Use the same procedures for the Furnace.

When using the AC, in the Auto mode the fan will run on high when the room temperature is 5 or higher than the thermostat setting. When the room temperature drops to within 4 or less than the thermostat setting, the fan will stop for a few seconds the start again in the Lo mode.

Hope this helps.
Perfect thanks. This is the same thermostat. I didn't realize there were various FAN settings. I thought it was simply Fan, Cool, or Furnace. I didn't think to check if there were options when Fan was selected.

Cheers
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Old 12-29-2012, 08:58 PM   #12
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Worked for me too, was driving us crazy. Went over the to fan setting and changed it to "Au" Just pulled our Sunseeker out for a New Orleans trip and couldn't figure out why the ac fan kept coming on and it didn't last fall. Just bought ours in the fall. I think the thermostat probably went back to a default setting after the battery going dead sitting in storage.
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Old 06-16-2013, 09:17 PM   #13
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This forum is great - first time using it for our new Surveyor 305. We just had this "problem" this weekend! Believe it or not, in June in PA, we had to run the AC during the day and furnace at night. Couldn't figure out why AC was kicking on. Our thermostat is the same one that GRHODES50 posted. Hopefully this will correct our "problem"! Thanks again!!
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Old 09-25-2016, 08:17 AM   #14
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Quote:
Originally Posted by grhodes50 View Post
Do you have the Dometic Digital thermostat?


If so, then I agree with what dunnnc had to say.

Here's some info that might help you.

Use the On/Off Mode button to select FAN. Then use the +/- button to select either Hi, Lo or Auto.
When using the AC and the fan is in the Hi or Lo setting it will run continuously while the compressor will cycle on and off.
In the Auto mode the fan will cycle on and off as well.

If the fan is set on Hi or Lo while using the furnace the AC fan will run continuously, so be sure to set the fan on Auto when using the furnace.
You can, however, leave the AC fan running while using the furnace to help with condensation problems.

After setting the fan, Use the On/Off Mode button to select COOL for AC use. Use the +/- button to select the thermostat temperature setting.
Use the same procedures for the Furnace.

When using the AC, in the Auto mode the fan will run on high when the room temperature is 5 or higher than the thermostat setting. When the room temperature drops to within 4 or less than the thermostat setting, the fan will stop for a few seconds the start again in the Lo mode.

Hope this helps.
Love this forum! We just had this problem and you were able to solve it for us. Thank you!
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Old 09-29-2016, 09:44 PM   #15
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I'd like to thank the forum, not because it fixed a problem I had but because it fixed a problem i was about to have and didn't realize it yet. I went out and checked mine, didn't realize it was on high, when I turned the thermostat on to heat it would of done exactly this. So you guys fixed it before it was a problem.
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Old 10-09-2016, 12:42 PM   #16
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Thanks! Saved me time digging thru the owners manual! 2016 201RBS. Love it and the forum.
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Old 10-10-2016, 03:51 PM   #17
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Just wanted to send out a big thank you to everyone who follows and responds to FR problems that are posted. I had similar issue with my AC coming on when I turned on our back furnace and went to the FR Forums site to check to see if anyone had similar problem . Sure enough I found SCOC's post and replys and had my answer. This isn't the first time the forums have helped me out
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Old 10-21-2016, 09:12 PM   #18
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Quote:
Originally Posted by grhodes50 View Post
Do you have the Dometic Digital thermostat?


If so, then I agree with what dunnnc had to say.

Here's some info that might help you.

Use the On/Off Mode button to select FAN. Then use the +/- button to select either Hi, Lo or Auto.
When using the AC and the fan is in the Hi or Lo setting it will run continuously while the compressor will cycle on and off.
In the Auto mode the fan will cycle on and off as well.

If the fan is set on Hi or Lo while using the furnace the AC fan will run continuously, so be sure to set the fan on Auto when using the furnace.
You can, however, leave the AC fan running while using the furnace to help with condensation problems.

After setting the fan, Use the On/Off Mode button to select COOL for AC use. Use the +/- button to select the thermostat temperature setting.
Use the same procedures for the Furnace.

When using the AC, in the Auto mode the fan will run on high when the room temperature is 5 or higher than the thermostat setting. When the room temperature drops to within 4 or less than the thermostat setting, the fan will stop for a few seconds the start again in the Lo mode.

Hope this helps.
I know this is an older post, but wanted you to know I had the same thing happen in my new Crusader 315. The fan was set on high causing both fans to run. Set it on auto and no problem. My first experience with an all digital thermostat. Heading South so switch back and forth between heat and air. Thanks for the help
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