Strange Atwood Heater Symptoms

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CncDean

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Vernon FL
Hello,
So I have an Atwood 8535 in a 2001 Four Winds 38’ Toy Hauler.

It’s been working fine for a month or so. It recently had a new motherboard put in by old owner.
I put a new igniter electrode In it when I got it. It’s been working fine ever sense.
On start up the blower motor would squeal. I sprayed the center wheel arbor with penetrating lubricant and it quieted up.
Most recently it was running but kept going out. I thought the tank was out so I switched it to the other full tank. It was still lighting for a few seconds and going out. Then trying again. It was constantly doing this, more than 3 times and a lock out, until eventually it would catch and stay lit.
But even while lit, it’s BARELY warming the camper up. It’s usually very quick. The air flow from the vents are low. There’s warm air coming from them but it’s usually hot. Too hot to stand on while it’s going.
What does this sound like to you?
The constant on and off made me think of flame sensor. But the low flow makes me think the blower motor is on its way out. I sprayed the blower again because it felt like there was some resistance when I spun it by hand. But if the blower wasn’t strong enough, wouldn’t that cause an over heating problem? It’s been running for an hour now.
If this is a blower problem then fine, I’ll replace it. But the constant on and off until it stayed lit made me think of another problem.
Any thoughts?
Thanks
 

NY_Dutch

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A dragging blower motor could drop the air flow low enough to open the sail switch shutting off the gas valve. If the flow is marginal, it could be opening the switch until the fan speeds up again closing it, allowing the valve to reopen and the gas to relight.
 

CncDean

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I think either way I’ll buy a new blower because it was always on my list of to dos since it was squealing.
 

CncDean

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Vernon FL
Could this be a bad regulator at the tanks?
I noticed that the automatic switch window is always red even when it’s full. Sometimes it makes a squealing noise at the regulator.
 
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Kirk

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I suggest that before you work on it too much, download a copy of this Atwood service manual from Bryant RV Service.

Your furnace has what is called a sail switch which is a switch that is actuated by air movement from the blower to make sure that there is sufficient air movement before it will allow the propane supply valve to open or the ignition probe to fire. If the blower were not moving enough air the furnace would never open the propane supply valve or attempt to light the fire. If it is starting the fire at all, then the sail switch must be closing and and so the blower has to be working.
Could this be a bad regulator at the tanks?
Absolutely it could. In fact, too little propane would cause exactly the symptoms that you have. Have the propane supply pressure checked by a qualified RV tech as it is quite likely the regulator is the problem.
 

CncDean

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I called a local tech and he said that regulators are in short supply but he has one. He wanted to make sure that it may be that as a problem. He suggested that I turn on the stove top and watch the flames when the furnace kicks on.
When I did this there was no change in the flame so he said that it’s not a restriction in the regulator. He does think that it should eventually be replaced in the future because the site glass for an empty tank always shows red.
He thinks it’s more plausible that the weak fan is the culprit but also thinks that there could be a problem in the gas line pigtails at the tank since they’re making a high pitch squealing noise that is probably the check ball.

So for now I’m going to wait until the blower motor comes in and I also ordered some new pigtails. I’ll wait on the regulator for now.
 

8Muddypaws

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Do you or the previous owner have pets? Pet fur has a way of slowing fans. I've recently had the pleasure of disassembling two heaters to remove the fur wrapped around the spinning parts. They worked fine afterwards.
 

Rob&Deryl

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I filled a propane tank this morning at a propane supplier - ya know, big tanks a delivery tank trucks.
While in the office paying, I noticed a large number of regulators and switch over valves on shelves. They had everything.

Could be RV dealers are short because they didn’t stock much and after using up the few they had, are now waiting for resupply.

I notice the the Camping Worlds seem to be out of everything but other sources seem have availability. For example, I need a replacement Furion thing. None of the rv places have em but I can get one through Amazon in 4 days.
 

CncDean

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Do you or the previous owner have pets? Pet fur has a way of slowing fans. I've recently had the pleasure of disassembling two heaters to remove the fur wrapped around the spinning parts. They worked fine afterwards.
I’m unsure whether the previous owners had pets and yes we have some pets ourselves. When I got the camper there was an issue and I took the unit out and cleaned it thoroughly.
I think the blower motor just saw the end of its days.
 

CncDean

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UPDATE:
So I put the new blower motor in and replaced both LP pigtailed at the tank.
Same problem.
Ignition, a little poof from the flame, then nothing. It continues to try to start it with no luck.

I checked the burner while I had it apart and it’s in good condition. No holes or excessive rust.
So what does that leave us with?
The regulator? The technician said it’s probably not the regulator since we put the stove on and there wasn’t a drop in the flame. But that’s all I can think of.
Any thoughts?
 

JayArr

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Does the fan run at full speed/volume when it tries to start?

Maybe it's not getting a full 12V and is running slow causing the sail switch to disengage. This may be a battery or wiring problem.

When you installed the new fan was there any way to add a pair of wires and run them out of the furnace to monitor the voltage while it's running? An old power cord would do. That way you could put the furnace back in but also put a voltmeter on the wires and measure what the voltage to the fan is when the furnace kicks on.
 

CncDean

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The motor runs and blows smooth and forcefully. I’m not sure that the fan is the problem here since the gas and igniter are activating.
My assumption is either the regulator or maybe the flame sensor. Although I did replace the igniter/sensor about 6 months ago. Not to say that it couldn’t be faulty.
I suppose that the only way to know about the regulator is to either have the volume/pressure of it tested, or get a manometer and test it myself. But in that case I’d be paying like $30 for a cheap one and if it is a regulator issue, another $70 for that. I would probably just buy another one since the one I have, the site glass to indicate a full and empty tank is always reading red. So something funky is going on there.
 

CncDean

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Does the fan run at full speed/volume when it tries to start?

Maybe it's not getting a full 12V and is running slow causing the sail switch to disengage. This may be a battery or wiring problem.

When you installed the new fan was there any way to add a pair of wires and run them out of the furnace to monitor the voltage while it's running? An old power cord would do. That way you could put the furnace back in but also put a voltmeter on the wires and measure what the voltage to the fan is when the furnace kicks on.
I tested the volts at the two wires from the motor. It’s 11v. I’m connected to shore power and battery volts are over 13v.
What could cause low volts to the motor? I’ll read around.
 

CncDean

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That’s the only way? Nothing to do with the control board that I should worry about?
It was working perfectly fine for over a month and then just one day it started doing this.
 

CncDean

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Is there any test I can do to trace where the voltage drop is coming from?
I’m going to try to hook the fan to a battery and see if it stays lit. If it does then I’ll start hunting down grounds.
 

CncDean

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So after hooking the blower wires to a battery the result is the same. Clicks and puffs but won’t stay lit.
Is the final assumption that it’s not getting enough gas?
There’s not much more that can cause a no start but have spark, gas, and temporary combustion.
Other than a flame sensor which was replaced 6 months ago and looks good.
 

TonyL

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A damp or cracked probe will allow high voltage to spark and ignite, but not conduct the milliamp signal that shows the furnace has lit.
 

Kirk

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I have seen an ignition probe with a cracked ceramic supply the spark to start the flame burning but then after a short time as it heats up the carbon in the crack shorts out the tiny voltage that it returns to the control circuit board and so it thinks that the flame has gone out and turns off the propane. If it were mine, I'd try a new ignition probe.
 
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