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Old 12-07-2005, 06:29 PM   #1
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I have 2 Atwood #8525-IV DCLP through the wall furnaces and one of them only blows cold air.
RV is at my house, plugged into 30amp electric service.

Here's what I've done so far:
1. Listened carefully to the bad furnace at startup. There is no sign of sparking or clicks and no propane smell of any kind. Assuming there is no attempt at ignition.
2. Checked the batteries - 2 12v Deep Cycles show good voltage on the panel, the interior lights are bright and the other furnace works properly. Didn't measure the voltage at the batteries
3. Checked the propane. Nearly 3/4 tank shows on the gauge(136lbs). All 3 stove burners turned on at once and all show good blue flame
4. Took the outside cover off and discovered that the wiring color code doesn't appear to match the diagram in my manual. Took a series of digital photos and am going to try to figure out what the differences are.

The ladder electric diagram shows the 12 volts goes through a limit switch and the sail switch to the integrated circuit board and from there to the electrode and propane valve coil. Tomorrow, I should be able to determine whether the board is seeing a strong 12 volts or not (as soon as I'm sure exactly which wire it is coming in on) and this should divide and conquer the switches. The only other thing that I considered is running an external ground jumper directly from the frame point just to eliminate that.

What are my odds? Sail switch? Limit Switch? Bad ICB? It is sleeting hard here now and we are not supposed to be above freezing until Friday. Unfortunately, this is the furnace that heats my tank enclosure. I have the back furnance on and a cermaic heater up front, too. I left the bad furance on so that the fan at least circulates the air through the tank enclosure. I'm hopeful this is something I can deal with fairly quickly.

Thanks for any thoughts that you can provide.
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Old 12-07-2005, 06:29 PM   #2
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I have 2 Atwood #8525-IV DCLP through the wall furnaces and one of them only blows cold air.
RV is at my house, plugged into 30amp electric service.

Here's what I've done so far:
1. Listened carefully to the bad furnace at startup. There is no sign of sparking or clicks and no propane smell of any kind. Assuming there is no attempt at ignition.
2. Checked the batteries - 2 12v Deep Cycles show good voltage on the panel, the interior lights are bright and the other furnace works properly. Didn't measure the voltage at the batteries
3. Checked the propane. Nearly 3/4 tank shows on the gauge(136lbs). All 3 stove burners turned on at once and all show good blue flame
4. Took the outside cover off and discovered that the wiring color code doesn't appear to match the diagram in my manual. Took a series of digital photos and am going to try to figure out what the differences are.

The ladder electric diagram shows the 12 volts goes through a limit switch and the sail switch to the integrated circuit board and from there to the electrode and propane valve coil. Tomorrow, I should be able to determine whether the board is seeing a strong 12 volts or not (as soon as I'm sure exactly which wire it is coming in on) and this should divide and conquer the switches. The only other thing that I considered is running an external ground jumper directly from the frame point just to eliminate that.

What are my odds? Sail switch? Limit Switch? Bad ICB? It is sleeting hard here now and we are not supposed to be above freezing until Friday. Unfortunately, this is the furnace that heats my tank enclosure. I have the back furnance on and a cermaic heater up front, too. I left the bad furance on so that the fan at least circulates the air through the tank enclosure. I'm hopeful this is something I can deal with fairly quickly.

Thanks for any thoughts that you can provide.
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Old 12-08-2005, 12:30 AM   #3
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Hopeully it is just a bad connection on the board. If you can get to the high limit thermal fuse, with power of and one wire removed; ohm it out, it should be closed. If not you will need a new one. Does the furnace motor run?
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Old 12-08-2005, 04:46 AM   #4
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Thanks for your response, Mike. Yes, the furance motor runs - sorry I wasn't more clear about that. When I left it on last night to circulate the air it was because the fan does come on. I have a supplemental electric heater at the return duct so it is pulling in warm air that I hope is being sent around the tanks.

I may be able to get to the high limit switch wiring but last night, while it was sleeting so hard, I couldn't trace that wire. As I said, the colors of wires used in the diagram definitely don't match the colors in the actual unit so I was having to compare them one at a time to make sure what I'm examining. From my digital photos, I think that I've figured out what goes to what so it should only take me a few minutes to do some isolation as you suggest.

I have a couple of MH dealers within a few miles of me. I can only hope that one of them will have the part(s) that I need. I did pull the connector off the board, clean it with DeOxit and put it back last night but that was no help (I'm never that lucky).

Thanks again,

Charlie
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Old 12-08-2005, 07:08 AM   #5
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We had the same problem on one of our Atwood furnaces. The blower fan would kick on, but the flame would not light. It turned out to be a bad sail switch. After I replaced the sail switch, we've had no further problems. Now the blower fan kicks on, and, after a 5-10 second delay, the igniter lights the LP gas.
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Old 12-08-2005, 02:08 PM   #6
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Thanks for the tip, Tom. I had a few minutes to work on this problem today. Here is what I now believe:
1. With my meter, I can see 12volts on the input to the ICB after a delay following the fan start. According to my diagram, the 12volts comes through the limit switch and the sail switch so both of them should be good.
2. I physically swapped the ICBs between furnances and the back one is running fine on the board that was in the front.
3. I pulled the burner on the front furnace, removed and carefully examined the orifice. It sure looks clear to the naked eye. I also examned the output and it isn't blocked either (I had mud daubber screens on).
4. I measured the ignitor with an ohm meter and it appears correct - not open or shorted. Since I hear no clicks or sparks, I'm still not sure about this.

I'm going to limp through again tonight with the back furnace and the supplemental heater. Hopefully, I get a chance to work on it a little more tomrrow. When I do, I want to check the coil on the propane valve. It is supposed to be above freezing by tomorrow afternoon and into the 60s over the weekend. That should make the troubleshooting process a little more bearable.

The biggest puzzle for me is that I cannot smell propane. If the board is trying to trying to light the burner and it fails, I would think that I would get at least a whiff of propane at the output. I've never smelled anything. I've toyed with pulling the wire off the ignitor on the rear furnace, just to see the results. If I really get frustrated, I might swap the burner units between furnaces, too.

Any other thoughts?

Charlie
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Old 12-09-2005, 06:13 AM   #7
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That "whiff of propane" can be very elusive and can easily be missed unless you can get a sniffer right down at the orifice.

Were you able to verify you have 12.6V at the propane valve relay?

The lack of clicking from the igniter is a bad sign. You don't always hear it when the covers are on, but with the unit opened up you should hear it. Since the circuit board works and you have power through the sail switch, I would guess either a bad connection to the igniter or a bad igniter. I don't recall the ohms spec for the igniter, but they can be bad without showing a dead short or open.
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Old 12-09-2005, 08:00 AM   #8
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Thanks for your ideas, Gary. Today's troubleshooting will include using an RMS meter instead of my standard one and I want to focus on the 12.6 volts at the propane valve. I cannot hear the ignitor on the working furnace either but I'm assuming that it only clicks once because that furnace fires with no hesitation. I have a professional combustion gas dectector that I've used for natual gas inside my home (I've put in gas logs, gas dryers and gas water heaters) and plan to try that to see if it can detect any propane smell on the bad furnace. I cannot tell whether the board is trying 3 times or just once to ignite before shutting down. The fan doesn't run for too long though.

Worst case, I have the ignitor from the working furnace and can swap it to the bad furnace, though that will be pain. I've had the connector off of the ignitor a couple of times so I don't think that my problem is a poor connection there. The gap is more than 1/8" and I want to go back over my manual to double check what that gap should be.

Hopefully, the weather forecast of mid-50s for today will be accurate. That will be a lot easier to work in than the low 20s have been.

Charlie
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Old 12-10-2005, 09:23 AM   #9
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Update: Today, in a little warmer conditions, I started troubleshooting the furnace again. I initially lead myself astray by measuring the input voltage to the ICB with the connector off. In that condition, it would read 12.6. With the connector on the board, the voltage dropped. I discovered that problem is in the sail switch and am ordering one on Monday. There is obviously some sort of damage to the internal contacts on that switch.

Thanks for all of your help.

Charlie
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Old 12-10-2005, 10:41 AM   #10
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Charlie,

Glad to hear that you've narrowed down the problem to a bad sail switch. Our sail switch went bad too; I guess the internal contacts wear out over time. I even tried running some cleaning solvent inside the sail switch, without any success. Our furnaces are circa 1992 so we got our moneys worth out of them.
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Old 12-10-2005, 04:21 PM   #11
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Charlie: Thanks for the follow-up, something to file away 'just in case'.
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Old 12-11-2005, 07:28 PM   #12
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Looks like you got it figured out but I was going to suggest the sail switch. I had the same problem and after playing with the sail switch it started working. I guess a bit of dust got in the contacts. The ironic thing about when mine failed, it not only got really cold that night and the heater was blowing cold air, but I also left a window wide open that night. We were nice and cozy the next night after I figured it out.
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Old 12-15-2005, 07:51 PM   #13
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Update: my wife picked up the new sail switches for me while I was on a business trip this week and I installed the one in the bad furnace this evening. While I had it apart the last time, I did the yearly maintenance routine described in the manual and adjusted the igniter contact gap. With the new switch in, the furnance fired right up and ran through a couple of cycles with no problems. I'm putting the second switch in my goodie box in case the back furnace decides to do the same thing. I ended up paying $4.15 for both switches ($2 each) so this has got to be one of the cheapest repairs that I've done on the MH. And, I managed to finish it just in time for the next cold snap.
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