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Furnace Doesn't Work In Sub-freezing Weather

furnace

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13 replies to this topic

#1 greencurry

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Posted 13 December 2011 - 06:48 PM

I have a 2005 Monaco La Palma and the furnace will not work in very cold weather. When the outside temp drops to the teens or twenties, the furnace will try to ignite and then quit. It will try for two more times before it quits trying. Since it only fails to ignite in cold temps, it is hard to replicate at the repair shop. I works fine when the temps are not so low. Any ideas?
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#2 vtbigdog

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Posted 13 December 2011 - 09:49 PM

Assuming you have access to the ignitor, I would check to see if you can see or hear the spark . If it is sparking I would have the propane feed checked or adjusted.

If you have the make and model or the furnace I would check the manufacturers site as they will have top-notch manuals for diagnosis.
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#3 wolfe10

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Posted 13 December 2011 - 10:05 PM

Since the furnace ignites, then quits, you can (at least temporarily) rule out low battery voltage, bad sail switch, etc.

First place I would start is to test propane pressure with a manometer. It is not unusual for the heavier hydrocarbon contaminants in propane to clog a regulator and the colder the temperature, the more that light viscosity grease-like substance thickens and can reduce gas pressure.

If you don't have a manometer, make one OR just replace the propane regulator-- under $25. Be sure to get the correct one-- there are two styles. The vent (quarter sized screen part) MUST, repeat MUST point down. So, if the regulator is installed horizontally , the vent will be perpendicular to the regulator's long axis. If installed vertically, the vent will be in line with the long axis of the regulator.
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#4 Guest_BillAdams_*

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Posted 14 December 2011 - 12:17 AM

Do you have a propane cooktop? If so, turn it on and let the flame run for a bit and then try lighting the furnace again. If the regulator is working properly the stove should remain lit (try both burners just for fun). If they do it's unlikely that the regulator is a problem. There is a "sail switch" in the circuit. This switch is blown open by the air flow which is required before the furnace will come on. Are you getting good air flow as soon as you turn the furnace on? If you can locate the sail switch, does it click when moved?
Do you have any additional information?

#5 chucknewman

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Posted 14 December 2011 - 01:52 AM

If the sail switch is defective, the furnace's control board's starting sequence will not get to the spark function. When it does spark, it will try three times. If no current from the flame sensor, the board locks out. A safety design.

You may have a regulator issue when very cold and Bill's suggestion with the burner is good. You should have a mostly blue flame with a small blue cone within the larger flame. If the flame does not look right, then I agree you need a manometer check.

What I have experienced in cold weather are sticking solenoid LPG vapor valves. The control board opens this valve as it begins the spark sequence -- lighting the burner in normal operation.

Assuming you have good DC voltage, the next time it sparks but no flame, warm the fuel line solenoid with a heat gun or hair dryer until it is fairly warm to the touch. Then start the furnace. On some solenoids you will hear it "click" to the open position.

It that doesn't work, you need to manometer the LPG system. If that is OK, you will require volt and ohm testing of the board, switches, and solenoid.

Most solids contract as they get colder and poor solder joints and/or crimp connections sometimes open or increase resistance to upset the logic circuits on the board. Tell the shop to get a can of "circuit freeze" or something similar at their local electronic part store. It cools circuits and components quickly. Great stuff for troubleshooting cold related problems.

Chuck
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#6 StellersJay

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Posted 14 December 2011 - 06:49 AM

Greencurry,

I had a similar problem with my motorhome during the first winter I had it. The furnace worked fine when the temps were warmer, but when they approached freezing, the furnace would not light. The furnace went through the same lighting sequence you described. It was too cold for me to work on the furnace, so I took it to an RV service shop near us. They found that the air passage through the heat exchanger was clogged with dirt dobber nests. The previous owner of our motorhome must have stored it in an area with lots of dirt dobbers, since they had build their mud nests in many concealed places on the coach. Apparently, when the ambient temps were warmer and the air lighter, the fan could push enough air through the heat exchanger to activate the sail switch. With the cold, heavy air, the furnace fan couldn't force enough air through the restricted heat exchanger to open the sail switch. The RV shop cleaned the heat exchanger, I installed a screen over the air inlet/outlet on the furnace heat exchanger, and all has worked well since.

This may not be your problem, but I pass it on for what it's worth.

Sam
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#7 wolfe10

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Posted 14 December 2011 - 09:48 AM

Sam,

A slight clarification. The dobber nests, would, as you say be in the combustion chamber/heat exchanger section of the furnace. In other words the part of the furnace system accessible to and only to the outside of the coach. The sail switch is in a totally different air flow area/fan area where inside air is forced through the "inside part" of the furnace and back into the coach.

There is absolutely no connection between the two areas-- if there were you would have combustion gasses getting into the coach. I have never seen dobber nests in the "inside part" of a furnace. I there are, they have to enter and leave through the interior of the coach.

It is quite possible that the dobber nests degraded furnace performance at one of several key areas that would account for your symptoms. Burner/ gas jets obstructed so thermocouple would not get hot enough to keep the furnace lit. Thermocouple itself "insulated" by dobber nest, etc.

Brett
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#8 StellersJay

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Posted 15 December 2011 - 06:27 AM

Brett, of course, you are correct. The sail switch is on the "clean" air side of the heat exchanger. The air inside and outside the heat exchanger do not mix (unless there is a hole in the heat exchanger due to rust through or another defect). My partial plug-up with dirt daubber nests was on the gas side (side accessable from the two ports on the outside of the coach at the furnace door - on our rig).

Thanks for clarifying my post!

Sam
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#9 smokeater75

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Posted 15 December 2011 - 02:14 PM

I take my motorhome out every 2 wks in some pretty cold weather, -15 to -36 I found that when it was really cold that my furnaces seem to cycle on then off a few times before they finally stayed lit. When I took it in for my yearly appliance test, I mentioned this to the tech. He told me to start up my two burner gas stove first and let it run for a few minutes and then start my furnaces. It seemed to do the trick. Last time I took the motorhome out for a run it was -28 with a -39 wind chill and they worked just fine. Good luck, Smokeater75.
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#10 Koliver

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Posted 15 December 2011 - 03:01 PM

I will assume that you have a diesel furnace. I had one on my boat that behaved the same, ie poor ignition in cold weather, to no ignition in really cold weather. Exactly when you need it most. Eventually realized that it would ignite fine after running for a while, long enough to warm the fuel in the tank that was luckily located in the engine room, alongside the furnace. I then tried using kerosene instead of diesel from the main tanks, to prove the theory. If you have only diesel #2 in your fuel tank, you will continue to have the problem. If you can move up to #1, or Home heating fuel, your furnace will perform better. I don't know if you can get an igniter that is better suited to running #2. Check with the furnace mfg. For a temp fix, try a jug of kerosene.
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#11 wolfe10

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Posted 15 December 2011 - 04:41 PM

Koliver,

Actually, I suspect the OP has a propane furnace.

Brett
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#12 chucknewman

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Posted 16 December 2011 - 01:32 AM

Rather than change to #1 diesel just put an additive into your #2 so it won't gel at really low temps. Available at all truck stops.

Keep in mind some home furnaces (NG or LPG) use the equivalent of a sail switch in the burner compartment to sense exhaust air flow. It actually is a vacuum switch connected to the fire box by a 1/8" vacuum line. When these units will not light the problem frequently is soot, dirt, or bugs in the vacuum line. Has saved me a service call on several occasions.

Chuck
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#13 wolfe10

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Posted 16 December 2011 - 08:29 AM

I have sent the OP a Private Message asking for clarification on that furnace he has, as we are following two very different lines of ASSUMPTIONS on what he has.

Brett
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#14 Guest_BillAdams_*

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Posted 16 December 2011 - 11:26 AM

As an aside, using home heating oil in your RV is quite illegal as you would be avoiding the required over-the-road taxes so I highly recommend against this option.
It also appears that the 2005 version of the La Palma has a gas engine which would dictate a propane furnace.





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