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Old 02-20-2022, 12:59 PM   #1
Sideways34
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Furnace help!!!

Long post warning!

I have a 2013 Keystone cougar with which due to unfortunate circumstances I have had to full time now. I have a problem with the furnace. It started close to a year ago and I am at my wits end. Was having problems with it intermittently not working. It finally gave up the ghost completely. So I did some digging and found a "technician" to work on my rv. Now for the fun part!

The technician said it was the sail switch. He pulled out the furnace and had to cut wires to do so. Ray with "love your rv" told us how to do it. He cleaned the sail switch, it had fluffies on it. While said technician was stripping the 4 wires to reconnect them he pulled 1 of the blue wires completely out. Upon inspection the end he pulled out was not stripped, just clipped. The wires run up behind the fridge. We pulled the fridge panel off and found that the wire was encased in expanding spray foam. There is no blank wire it could have been connected to. We hooked the 3 remaining wires back together and it worked. (Kinda) Said technician also brought his dog with him who knocked the unit over while it was out breaking the squirl cage cover. So a little super glue,$250, he put it back together and was on his way.

The furnace would power on and run 1 heat cycle then shut down and not cycle again until the t-stat was reset.

I went to an rv dealer and picked up a control board, a sail switch, a thermal switch and a squirl cage cover. $289

I installed the new control board and cage cover and it still acted the same way. I few days later i also purchased a regulator $108 and installed it. Same problem. Frustrated, I contacted a different technician.

Que tech #2. He said it was the sail switch. He replaced the sail switch and unloaded me for $250 with my parts. Still same problem. I installed the thermal switch, same problem. I called tech #2 and told him it didn't work. He said it was the ignitor. He said he wouldn't charge me a service call for the second time. He came out and installed an ignitor while unloading me for $193. This time it was a little better. Would recycle but would not run all night. I have to get up about 5 or 6 times a night to get warm again every time.

Frustrated even further I purchased a complete new furnace.

Now for this weekend, I uninstalled the existing SF-30FQ and installed a new RP-35Q/FQ. The price was right $400 I know it's not the exact same but it is close enough, if not an upgrade. I wired in the new one and the 3 wire configuration doesn't work. Uninstalled the RP and reinstalled the SF. Low and behold the SF no longer works with the 3 wire configuration. Im frustrated and angered enough to spit fire. Can anyone help?
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Old 02-20-2022, 02:15 PM   #2
chuckster57
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Welcome to the forum

So sorry you have had all this trouble. If your trailer DOES NOT have incommand then the two blue wires are needed. They are the signal to/from the thermostat for heat. the four wires are:

12V positive to control board
12V negative to control board
Blue signal TO thermostat
blue signal FROM thermostat

With either unit, put 12V to the power and ground, then jumper the two blue together and see what happens. IF the furnace fires up and runs then the issue is the "missing" blue wire.
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Old 02-20-2022, 02:26 PM   #3
Sideways34
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Thank you for the welcome.

So yes, when I connect the blue wires on both furnaces they both run and cycle as they should.

On the SF both wires are blue and 1 has 13.65v. The other one has nothing. So when the hot is touched to the dead, it works. Now to the tstat wire, it has 13.40v when tstat says heat on. When I hook the tstat sig wire to the dead side it won't fire. I am confused by this because the ground is held through the 12v neg for both.

I also can't figure out why it ran in the 3 wire configuration for 5 months and now won't.

Next question is, what is incommand?
Thank you very much
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Old 02-20-2022, 02:34 PM   #4
Sideways34
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Here are pics of the wire that got pulled out
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Old 02-20-2022, 02:38 PM   #5
Sideways34
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Here is a better pic of the end
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Old 02-20-2022, 02:45 PM   #6
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In command is A system built by ASA (Jensen) for central control of the trailers different systems, since you don’t have it, count your blessings.

Blue wires: the one with 12V is coming out of the furnace control board, and if you connect them the furnace should run and NOT shut off until you disconnect them from each other.

Simple explanation: you turn thermostat to heat, turn it up, when you turn it UP the circuit is completed and 12V is sent back to the board telling it to go ahead. When set temp is reached, the circuit is broken and the control board goes into cool down/shut off mode.

I have no explanation as to why it worked with only 3 of the 4 wires hooked up.
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Old 02-20-2022, 02:56 PM   #7
Sideways34
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Do you know or know where I can find where the 4 wires run or what they are hooked to behind the fridge? I can see 3 and where they go but the 4th is a complete mystery?

I also, in my wonderings of the interwebs found a mention of "forced voltage" using 3 wires for this use but can not find anything more about it.
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Old 02-20-2022, 03:08 PM   #8
Sideways34
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Another thing that has my attention is the gauge of wire coming out of my tstat is way smaller than the gauge of wire into the furnace. I would like to find out where and why the transition?
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Old 02-20-2022, 03:08 PM   #9
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I believe this wiring diagram will better explain the 2 blue wires. Remember, they don't go "directly to the thermostat" but rather are routed from the furnace to the control box in the overhead air conditioner. That is probably where the wire gauge transition occurs..

As an observation. It looks to me like the blue wire in your photo that "appears not to have been used" because the insulation isn't stripped away, probably was connected to a "knife blade type" electrical connector, possibly on the gas valve.
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Old 02-20-2022, 03:12 PM   #10
Sideways34
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JRTJH, Awesome. Thank you. I have that schematic and the one for the RP model. The wire was pulled from behind the fridge. The gas valve wiring is intact. But thank you for the a/c idea. I'm on checking that when I get back from buying another electric heater. It's going to get cold next week in Colorado.
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