furnace

Topic: furnace (Read 970 times) previous topic - next topic

furnace

October 26, 2013, 06:51:15 pm

I've read on this forum several times that the rear furnace on my 1991 U300 heats the water tanks in the basement so they won't freeze. Does anyone know where I can find a document that verifies this as a known fact? I just disassembled and cleaned my rear furnace in preparation for freezing weather but I can't see any evidence of heating ducts near the water tanks. I don't know where to find these basement ducts to visually verify it. My rear furnace was packed full of mud dauber nests, even around the electrode and inside the squirrel cage and all the passages where the gas and combustion air flow. I put it all back together and it lit right up and ran great on the first attempt. It hasn't run for many years so it stinks of burning dirt of course, but it works. Tomorrow I'll clean the front furnace, which sorta runs sometimes when it wants to... or sometimes it kabooms repeatedly shooting a spectacular blue flame out the exhaust causing my frightened neighbor to move his soft top Jeep further away... but I didn't burn his Jeep down... yet.

Re: furnace

Reply #1 – October 26, 2013, 08:13:10 pm

Scott,
You may know this but they make exhaust screens for the furnace that will keep the mud daubers out.

Mark

Re: furnace

Reply #2 – October 26, 2013, 08:21:43 pm

Scott, I seem to remember the front heater taking care of the tanks on our U280 and the ORED. I had to replace the front furnace on one of them because of a cracked heat chamber. Seems like there were ducts going everywhere from the front one under the sofa.

MAZ is right. Get those screens for sure.

Where are you now by the way?

Re: furnace

Reply #3 – October 26, 2013, 08:32:06 pm

My basements are connected with grills in the walls. You might follow the paths from compartment to compartment. I know on my newer U295, I have some heat vent tubes and grills. Some of the vent tubes are hidden behind the wet compartment, and tank cover panels.

Re: furnace

Reply #4 – October 26, 2013, 09:42:49 pm

I think I'll tape over the furnace exhaust vents in warm weather to keep the wasps out. There aren't any wasps in cold weather when I'll be using the furnaces. Now that I know how to take the furnaces apart and clean them it's no big deal anyway. It's a little tougher than cleaning the water heater. Maybe I'll call Foretravel next week to verify which furnace keeps the water tanks from freezing. I'd feel really stoopid if I froze the tanks cuz I ran the wrong furnace. It looks like I'll be spending the winter in beautiful (expensive) Santa Fe NM and it's supposed to freeze here next week.

Re: furnace

Reply #5 – October 26, 2013, 10:01:00 pm

Scott,
Here's how they are set up on a 95. They are plumbed from the rear heater and just dump onto the top of the water tank, into the waste valve area and the water pump area. Primitive but effective. Photo is of the waste tank compartment without the tanks.
jor

Re: furnace

Reply #6 – October 26, 2013, 11:26:41 pm

I didn't see any of those heat duct hoses on top of the water tanks in my coach when I looked today. I'll look again tomorrow now that I know what to look for. I've been running the rear furnace a little bit tonight trying to get the burnt dirt smell out of it. I noticed that it only lights the burner on about half the attempts. When it fails to light it runs the blower forever just circulating cold air until I turn it off and then back on again. The front furnace keeps attempting to light the burner forever if the flame fails. I wonder if the previous owner installed an aftermarket circuit board in the front furnace? The two units behave very differently even though they're apparently the same model.

Re: furnace

Reply #7 – October 27, 2013, 12:03:35 am

Scott, we had a furnace that was working great and then quit lighting. It would go through all the steps, but would not maintain a flame. It would keep blowing air, but would not provide heat.

It had been working in spite of some dauber nests, but part of the burner assembly was damaged by the nests and would no longer support a flame. Remedy was to install a new burner assembly and put on dauber screens.

Re: furnace

Reply #8 – October 27, 2013, 09:41:33 am

Greetings

I had to replace the igniter for the eletronic ignition on my 88. Same mud daubers, cleaned etc. The gas solenoid in the rear needed replacement, no flow of gas just fan running. Hope this helps.
The little screens that go over the exaust port are $5 and worth it.

Re: furnace

Reply #9 – October 27, 2013, 12:06:21 pm

I was actually considering removing the guard from the exhaust to increase the airflow in cold weather when I'm using the furnace. I'm at 7,000' elevation and the furnace has a tag that says it's designed for 4,400' and below, so the last thing I need is a screen creating additional restriction to airflow. I should probably install a smaller jet if the fuel mixture is too rich at this altitude. I'll probably borrow a Bacharach tester and do a carbon monoxide and oxygen test on the exhaust to see if it's burning efficiently. I'll definitely tape over the vents in warm weather when I'm not using the furnace from now on. I wish the previous owner had taped over them but it's been educational taking the furnace apart and cleaning it. It's actually a really good design. I noticed the intake air is preheated by being pulled in through the tube around the outside of the hot exhaust. That must boost burner efficiency considerably. I'm gonna clean the front furnace today and see if I can get it running properly, then I'll return to the rear furnace to see if it has a fuel problem or something. Maybe some dirt got into the jet or the gas valve?

Re: furnace

Reply #10 – October 27, 2013, 01:17:09 pm

Quote from: RRadio – October 26, 2013, 06:51:15 pm

I've read on this forum several times that the rear furnace on my 1991 U300 heats the water tanks in the basement so they won't freeze. Does anyone know where I can find a document that verifies this as a known fact?

I don't know of any documentation, but I do remember when I pulled my water heater I saw a heater vent right above it. It's the same ones that are used on the inside and is flush to the basement ceiling. I can see mine with a flashlight if I peek over the grey tank looking directly above the water heater.

Re: furnace

Reply #11 – October 27, 2013, 03:41:36 pm

I got the rear furnace to run again today and I looked in the water tank bay as the furnace was running. I can't see where the heat is coming from but I can feel heat blowing on my face from inside the bay. I'm sure I wasn't feeling the exhaust from the furnace. I guess that convinces me that the rear furnace is heating the water tanks, but I don't see the duct. As long as it doesn't freeze who cares how the heat gets in there. I just cleaned the front furnace and put it back together and it started right up. It's the same model as the rear furnace but it puts out a lot more heat. The front one only takes a few minutes to warm up the whole coach from stone cold to the point where I need to take my jacket off. The rear furnace warms the coach at a much more normal rate that I would expect. I noticed the front motor has a squeal in the bushings that goes away after a moment, perhaps due to age and lack of use. The rear motor has a barely noticeable little squeal just for a moment when it first starts. I'll probably have to replace one or both motors at some point. The motors say they've got permanently lubricated sealed bearings. Interestingly, the rear furnace started right up again today, it just won't start at night apparently. I wonder if I need to have a full tank of propane to get the furnaces to work properly. I'll see if I can find somewhere to top off my tank today. I have to go get groceries anyway and I want to start my coach and drive it every couple of weeks. I think I have about half a tank of propane currently. I can't think of any other reason why the furnace would run perfectly in the daytime but not at night.

Re: furnace

Reply #12 – October 27, 2013, 05:50:05 pm

The spec. sheet for your coach shows a smaller rear (16K btu) and larger (35K btu )front furnace. That would be why the coach warms faster with the front furnace, it being more than double the btu output.

When we have shore power included in our camp ground fees, we tend to use electric heat sources instead of our propane furnaces. When we have camped at below freezing temps, we use the furnaces and enjoy warmer floors as well.

Re: furnace

Reply #13 – October 27, 2013, 11:56:16 pm

Tank level won't make any difference. Could be bad thermostat or faulty sail switch but using the model number, download the manual with troubleshooting section and eliminate possibilities.

Pierce

Re: furnace

Reply #14 – October 28, 2013, 08:42:06 am

No bearings in the motor-- just bushings. Some have had success in oiling them with a light-viscosity non-detergent oil such as sewing machine oil.

Tell us how far into the cycle it gets. Here are the steps in order:

Thermostat "clicks"
Fan starts
Gas valve opens and ignitor clicks
Furnace runs and heats (until thermostat contacts open)

Brett

Re: furnace

Reply #15 – October 28, 2013, 08:51:49 am

Quote from: RRadio – October 26, 2013, 11:26:41 pm

I noticed that it only lights the burner on about half the attempts. When it fails to light it runs the blower forever just circulating cold air until I turn it off and then back on again. The front furnace keeps attempting to light the burner forever if the flame fails. I wonder if the previous owner installed an aftermarket circuit board in the front furnace? The two units behave very differently even though they're apparently the same model.

The front one might have a "Dinosaur" board installed? One of their advertised benefits is to fix the "forever circulating cold air" problem with OEM board.

Dinosaur Electronics Home. High quality circuit boards for RV appliances.

Re: furnace

Reply #16 – October 28, 2013, 10:57:15 pm

I went down to the propane dealer and he put 39 gallons in my 40 gallon tank

...oops! ...so let's see if the rear furnace will work in cold weather now that there's plenty of fuel. There's nothing wrong with the rear furnace when it's warm, so I think the problem was low gas pressure from the nearly empty tank. The rear furnace is at least 20' away from the gas regulator and the front furnace is much closer. By the way, don't trust the fuel gauge on the little TV tube, go out and look at the gauge on the tank itself. There's a circular window in the center of the tank with a tiny red indicator needle. When the needle is way over to the top right of the circular window the tank is full and when it's way over to the left side it's empty. The propane dude pointed it out to me today. Don't trust the diesel gauge on the dashboard either, look down into the fuel tank with a flashlight and see how many inches of fuel you have before the level goes below the fuel pickup tube. I just filled mine today and it was bone dry when I looked in there even though the gauge said I had about 1/8 tank of diesel... Yikes! ...on the positive side I filled up with diesel at $3.579 and propane at $2.50 ...which isn't too bad right now according to what I've read on the internet from around the country.

Re: furnace

Reply #17 – October 29, 2013, 10:19:32 pm

The rear furnace still doesn't work, even with a full tank of propane. I swapped the control boards but that's not the problem. The front furnace runs fine with the board from the rear furnace but the rear furnace still won't run with the board from the front furnace. I can hear the gas valve click open and I smell gas. I hear the ignitor sparking but it doesn't light. The only thing I can think of is the flame sensor rod might not be sensing the flame. I'll take the burner out and clean the flame sensor rod again. Maybe I'll order a new ignitor / flame sensor / burner assembly from the internet to see if that fixes it.

Re: furnace

Reply #18 – October 29, 2013, 10:34:59 pm

Those are exactly the symptoms I experienced on one of our furnaces. A new burner assembly fixed the problem. My recollection is that the old part had a screen that didn't look particularly bad, but was deformed because of improper heating caused by dauber nests.

Re: furnace

Reply #19 – October 29, 2013, 10:50:49 pm

Quote from: MAZ – October 26, 2013, 08:13:10 pm

Scott,
You may know this but they make exhaust screens for the furnace that will keep the mud daubers out.

Mark

As a side note, I saw a strainer at a Dollar Store and realized the screen was perfect to take out and use for an exhaust screen. I check it every now and then, but it is at least 5 years old and still looks just fine. I just poked it out of its frame and re-formed the stiff screen over the exhaust and closed the furnace cover.

Re: furnace

Reply #20 – October 29, 2013, 11:04:28 pm

Another option to keep critters out of the furnace and water heater when the coach is not in use is to buy a yard of cheap nylon screen at any hardware store.

Cut it to fit inside the outside appliance doors. Close the screen in. Be sure to remove before turning on the appliance.

Let's face it, they are not setting up housekeeping while you are using the coach-- it is only when NOT in use that they move in and build nests in the appliances.

$2 fix.

Brett

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