Furnace Connections

[Repo]

While replacing the board on my 8535-IV furnace the red, white and blue wires detached from the plug. The board is labeled Air,TH,NC, VI,Test,Ground. The yellow wire did not detach and matches up with ground. I believe the red comes from the gas valve and the blue is 12v to thermostat. The yellow appears to go to the sail switch. I am also curious what designations Air, TH, NC, VI represent. I look forward to any and all replies.

[Repo]

I bought a replacement board last year but was unable to get furnace to work. I discovered the on/off rocker switch was shot when I accidentally shorted the board out. This was also due to having just enough knowledge to be dangerous while working on the furnace. I had the circuit soldered and then was not sure if I now had two good or two bad boards. Factor in the wiring problem dyslexia learning disability and a good measure of stupidity and frustration. Now you are starting to get the picture. If it wasn't for the fact that a neighbor tipped me off to this site when my Refer was only working on gas I'd still be scratching my as- on this one. Thanks again and again and again.

[Old-Biscuit]

:S Murphy was an optimist. It's never a question of 'IF' it's always 'when' :B

Why were you having to replace board in first place?
What board did you use to do initial replacement?
WHY do you have so many boards????? :B

Glad that it is now not only working but very clean.........and you now have a good hands on experience with it.

Good Job!

[Repo]

8535-IV Update I made all the connections as suggested with another board I had and everything worked perfectly. ALL I had left to do was put the dam wing nut on that holds the circuit board in place before replacing the outside cover. 4 measly screws to completion. THEN IT HAPPENED... What's that saying. MURPHY'S LAW... The !@&$"@ wind nut fell into the blower assembly. Only to make a bad thing worse it fell inside the housing. All I had to do to retrieve it was pull the whole dam furnace out. at least I got a chance to inspect all the pertinent parts a second time. I should be able to pull this apart in my sleep next time. Thanks again for the help Old Biscuit and my buddy James.

[Repo]

Thanks a million. I will probably get to work on it this weekend. When my neighbor inquired about my resolution to this problem I told him I was waiting to hear from an old biscuit. I don't think he believed me.

[Old-Biscuit]

The way you have it wired is so wrong!!

You are keeping power on the gas valve via 12V thru t-stat contacts and not thru circuit board.
If main flame where to go out the gas valve would stay open due to direct power from t-stat, until you turned t-stat off.
The fault light is because the circuit thru sail switch/high limit switch is dead......but with direct power to gas valve furnace continues to run.

The problem with main flame going out after 5 seconds when the wiring was correct is because main flame is not being proved back to circuit board which then shuts off power to gas valve so it doesn't stay open without a proven flame.

Flame proving is done via the spark electrode.
*Main flame has to engulf electrode.....heats electrode and induces a milivolt signal back to circuit board proving main flame
*Electrode has to be clean
*Electrode has to be properly positioned...should be fixed when installed but should have a 1/8" gap between electrode and ground rod. The ceramic should not have any cracks.
*The wire between electrode and board could be grounded or bad
*The exhaust could be blocked causing unbalanced air pressure
*Gas pressure could be low causing improper flame height/temp (should be 11" WC with at least 50% of other propane appliances in service)
*Connector on circuit board not making proper contact

Here is a service manual for Hydro-Flame Furnaces........pg. 10 shows wiring for 8500 Series. LINK

[Repo]

Thanks for the input guys. My original notes indicated WHITE to AIR, BLUE to TH, open slot to NC, RED to VI, open slot to TEST, YELLOW to GROUND. NOW here is where it gets interesting? The flame ignites for no more than 5 seconds with the aforementioned wiring. The only way to make the burner stay lit is to run RED to the first position marked AIR and put the WHITE in the third position on the board marked NC. The furnace works great but there is a fault lite every 12 seconds indicating a problem with the sail switch. The furnace has only been run about 2 hours since I bought the trailer new because it would hardly ever ignite. I have not been able to obtain any diagram of the wiring online. I am using oil filled radiators in the meantime. They provide quiet constant economical heat. Looking forward to your thoughts....

[Old-Biscuit]

Red....gas valve
Blue....t-stat
White....Sail Switch
Yellow...ground

Air......Sail Switch (White)
TH.......T-stat (Blue)
NC.......N/A
VI.......gas valve (Red)

[jimw606]

This may help.
http://www.atwoodmobile.com/manuals/furnaces/MPD%2033179%20SP%201.08.pdf

[Mandalay_Parr]

Can you find an electrical schematic either on the cover etc or online? We could help you better if you had one.

[Repo]

CORRECTION...the white appears to go to the sail switch