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Old 12-03-2009, 06:34 PM   #1
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1970 27' Overlander
Ketchum Idaho , Idaho
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Heater turning to cold air in middle of night

our 70' Overlander orig heater works great except that sometime in the middle of the night it turns to cold air....

its going to get to freezing tonight...

we need some help figuring this one out



Thanks!
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Old 12-03-2009, 07:18 PM   #2
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All heaters will blow cold air at the end of a cycle. This is to cool the heat exchanger before the fan goes off. That should last about 1 min.

If your heater is blowing cold air for a longer period it may be an over heat switch opening. If that is the case it is time to have someone look at the heater as the over heat switch is a safety and realy should not have to come on unless something is wrong.
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Old 12-03-2009, 07:22 PM   #3
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St. Cloud , Minnesota
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Copper plumbing is more susceptible to frost damage.

weather.com says Carson City is headed to 22 degrees tomorrow (probably pre-dawn), 16 degrees on Saturday and 21 degrees on Sunday.

Your furnace has ducts that go down to the tanks - coverage may miss some spots if you are really borderline -- I qualify that as temps in the teens or below.

A furnace that is not working? Member Leipper (Reno?) measured temps in his Airstream after temps around 20 degrees overnight. His experience - without wind outside, you may not see temps inside go below freezing. But always judge that down at floor level. You actually are going lower by Saturday.

What I would do? Buy some RV antifreeze and fill your traps -- especially those at the floor; eg shower. Drain your fresh water tank -- add back a couple gallons of water and $20-30 of the cheapest vodka you can find. Run the pump, emphasizing the outside lines most. For instance, shower mixer valves in outside walls are more susceptible to freeze damage -- and extraordinarily hard to access once ruined. Unreliable furnace? Get an inexpensive space heater, plug in to 120 volts, and run the space heater with lower cabinet doors near plumbing opened.

Put a thermometer at floor level near your plumbing. Monitor it in the mornings to see what effect you are having. Vodka in the fresh water tank is easier to purge than RV antifreeze -- and potentially more interesting for the goldfish...
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Old 12-04-2009, 07:13 AM   #4
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A space heater with the AS furnace fan running will distribute the heat through out the trailer via the duct work.
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Old 05-04-2012, 10:48 PM   #5
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1975 31' Excella 500
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I have a problem with my furnace. When it is running it will blow somewhat cold air out of the inside vents and the exhaust outside is somewhat hot. Does anyone know what the problem might be? There is a flame but it looks like it may need to be adjusted because it is partially yellow.
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Old 05-04-2012, 11:20 PM   #6
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Quote:
Originally Posted by zenarmy View Post
our 70' Overlander orig heater works great except that sometime in the middle of the night it turns to cold air....

Thanks!
Pretty common problem on the older furnaces. Two or three things may be causing it.

1: low voltage. When the battery gets down, the voltage drops below the necessary range to keep the gas valve open. That is generally 10.5 volts. Cause is a low battery, poor connections, poor grounds etc. You will need as high a voltage AT THE FURNACE as possible. Voltage drop through the wiring makes it important to measure it at the furnace.

2: Slow blower speed due to low voltage (see above) which causes the sail switch to drop out, shutting the power off to the gas valve. Also, the blower speed might be slow, just due to old age.

3: This is the hardest one to find, and is generally solved by replacement rather than testing.... the high limit over temp klickson switch has become interminent. On your original no circuit board furnace, if the temp of the interior of the furnace goes too high (and this is common, due to small ducts and low blower speeds) there is a little switch called a Klickson (brand name) which will shut the gas valve off until the heat is dissipated by the blower. The real name is the "high temperature limit switch" These switches get old and tired and when they open, they shut the gas off, but when they close, the contact does not make good and the gas valve will not come back on. Often, when completely cool, and run through another cycle from scratch, they will start to work again, but then fail again. In other words they become intermintent, which can drive you crazy finding the problem.

So, on your old pilot light furnace, I am pretty sure one of those three things is causing your problem. There is a slight possibility that the gas valve itself is defective and is temp sensitive, but that is not too common.

Have fun!
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Old 05-04-2012, 11:49 PM   #7
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Quote:
Originally Posted by PotatoPeach View Post
I have a problem with my furnace. When it is running it will blow somewhat cold air out of the inside vents and the exhaust outside is somewhat hot. Does anyone know what the problem might be? There is a flame but it looks like it may need to be adjusted because it is partially yellow.
Get an air compressor or a clean out brush and make sure you haven't got a little spider-nest or something blocking the burner. After periods of non-use you can get things like that happening. Yellow flame means not enough air...
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