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Old 11-26-2004, 09:05 PM   #1
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Furnace Thermostat

In August I purchased a new 2005 Safari 25. I've been having difficulties with the batteries running down too quickly (I think).

Last weekend while camping the overnight temperature dropped to 40 degrees. The furnace kept the inside temperature very nice at 68 degrees but it seemed that the furnace was kicking off and on a lot. Has there been any issue with the airstream furnace thermostats (digital) not letting the temperature drop sufficiently before re-firing the furnace? This would cause the furnace to kick on again when the inside temperature had dropped very little.

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Old 11-26-2004, 10:43 PM   #2
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Our digital thermostat cycles the furnace quit frequently, however once the tables, cabinets and counter top get to the ambient temperature the cycling slows down. We put foil bubble insulation in the windows with the shades down and curtins shut which helps alot. Also covering the skyslights and fantastic fans with decorative foil bubble insulation held on with velcro aids in keeping the heat in.
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Old 11-27-2004, 12:43 AM   #3
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My older Safari (1971) has an excellent furnace, but it too cycles constantly in colder weather and from what I hear from others, that is the norm. For one thing, these things are not very well insulated compared to say, a house. So it runs a lot. But they also seem to cycle way more than necessary, and I think one reason mine does it is to cool down the heat exchanger.

For example: it runs for awhile to bring the temp up, reaches temp, then shuts off as it should. But then, because it has sat for a few minutes with no air circulation and all the built-up heat has nowhere to go, the overtemp switch kicks the fan on again to move some air and cool it down. It is not actually in a "heating cycle" although the air coming out feels warm for a minute or two then cools off. So, two cycles instead of one.

This is just my random theory for why it seems to cycle so frequently, although I agree that perhaps the thermostat "drop" is also too small, so it is trying too hard to eliminate temp variations, as you suggest. Maybe that can be adjusted.

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Old 11-27-2004, 07:22 AM   #4
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old style thermostats have what is known as an heat anticipator...this is set to match the amperage draw of the coil in the gas valve, but that is not in the airstream world, as i found out...the t-stat shortcycles and temp never is met b4 shutting off. so i set mine to acheive the longest run time possible...as for the fan switch, i dont believe it is adjustable...
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Old 11-27-2004, 09:18 AM   #5
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One of the biggest problems the newer Airstreams have is the placement of the thermostat on the wall that surrounds the refrigerator. The heat or cold within this enclosure does affect the performance of the thermostat sometimes causing an elongated (and frequent cycling) run times of the furnace, or airconditioner/heat pump.

The problem is the mounting plate and hole for the wiring allows air from the refrigerator enclosure to pass through the thermostat. This is especially evident when using exhaust fans. I sealed the thermostat wiring hole on my Safari with some silicone which helped somewhat. I noticed my Classic exhibits the same traits.

Jack
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Old 11-27-2004, 09:53 AM   #6
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Quote:
Originally Posted by norbert
as for the fan switch, i dont believe it is adjustable...
norby
With the heat pump, I set the fan to run on continuous low speed when the temperature is above about 35. This disturbs our sleep less than having the fan starting and stopping and also prevents blowing a short blast of cold air every time the heat pump starts up.

When it gets very close to freezing, I turn the fan on auto so that it is not running during the heat pump defrost cycles when it would really blow a blast of cold air. Below about 35, the heat pump provides heat pretty steady anyway except during the defrost cycle.

We have a unit rally next week. After that, the fuzzy sheets and the down comforter go on the bed until spring.
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Old 11-27-2004, 10:19 AM   #7
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john, how often are the defrost cycles?
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Old 11-27-2004, 10:30 AM   #8
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Defrost cycle

Quote:
Originally Posted by norbert
john, how often are the defrost cycles?
norby
The manual is in the trailer, in storage, so I'm going from memory.

I have only had it overnight in below freezing weather once and it seems to me that it defrosted maybe every half hour or so. I would hear the compressor start up but the fan would not be running. That was at the Blanco Xmas Forum rally last year when my water froze solid at the brass regulator overnight.

I had the temperature set at 68 degrees and it was quite comfortable with just the heat pump running. It never did get cold enough to do the automatic changeover to the propane furnace. I think it changes over at about 25 degrees outside.
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Old 11-27-2004, 10:37 AM   #9
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interesting...i did not know the control had an automatic change over...i would think that if one had 2 t-stats, you would efectively have a 2 stage heating system...
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Old 11-27-2004, 10:58 AM   #10
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Quote:
Originally Posted by norbert
interesting...i did not know the control had an automatic change over...i would think that if one had 2 t-stats, you would efectively have a 2 stage heating system...
norby
When it gets cold enough to endanger freezing the tanks, the thermostat changes over to the propane furnace. This is all programmed into the smart wall thermostat using a second thermostat located in the outside section of the AC. So there is really a dual thermostat in the system. Apparently the changeover point is different for different years of production according to numbers posted on this forum. I think my changeover is at about 25 degrees.

The wall thermostat has some additional smarts in that it will not restart the compressor without a delay after it stops to prevent blowing breakers starting up under load. This delay is a pain when you first turn the thermostat on or change the mode and it really did not need to happen.

At this point, the heat pump has become very inefficient anyway. As the outside temperature drops, the heat pump runs proportionately longer than the loss of heat through the walls just because of the inefficiency. As it nears the changeover point, it is running pretty much steadily anyway.
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Old 11-27-2004, 11:15 AM   #11
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Our classic does not change over to propane automatically. When it gets below freezing outside, a thermistor in the outside coils starts the outside coil defrost cycle about every thirty minutes and lasts several minutes. There is also a thermistor in the inside coils that shuts off the compressor should the coils inside begin to freeze up. This was a pain so I removed it now the compressor wont cycle off when cooling the inside. Should the the air flow slow down I manually shut the compressor off until the air flow is back to normal.
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Old 11-27-2004, 12:03 PM   #12
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old style thermostat/furnace in 04 CCD

This fascinating thread is really making me scratch my head. First, we don't have a digital thermostat. Just the old syle analog variety that must only control the furnace. In our house I replaced the old style analog thermostat with a digital programmable one. Can I replace the one in the trailer too? Having said that when we were out over this last week the furnace kept us warm during the night and didn't seem to be cycling the way you describe. Maybe I'm just missing it in my not fully awake state, but can you describe what happens? Is the integrated heat pump, digital thermostat and furnace only available in certain models? Could I upgrade to that (and would I want to)?

Learning something new everyday,
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Old 11-27-2004, 02:04 PM   #13
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Quote:
Originally Posted by silverback
This fascinating thread is really making me scratch my head. First, we don't have a digital thermostat. Just the old syle analog variety that must only control the furnace. In our house I replaced the old style analog thermostat with a digital programmable one. Can I replace the one in the trailer too?
Learning something new everyday,
Ken
Ken,
You can replace the thermostat. Here's an old thread regarding replacing the factory Atwood with a low cost Hunter unit.
http://www.airforums.com/forum...=&threadid=246

Regards,

Jack
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Old 11-27-2004, 02:13 PM   #14
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The problem with the heat pump defrost cycle is that it can't account for humidity and only activates by cold outside temperatures. (I also think about 35 degrees is the trigger and 30 minutes of continous run time.) In cases of high outdoor humidity and cold temperatures, the outer coils will freeze with moisture present in the air. Here is a picture of my freeze up last month in Branson. Outside air temps were in the low 40's. I came back from dinner out and found the trailer cold inside and the fan and compressor running. This was after two days of rain. Once the outside humidity subsided, the heat pump worked fine.

Jack
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