Furnace not working (Atwood/Hydro 8531-IV)

1) Sail switch stuck.
2) As furnace is 12 volt I would check for a blown fuse
3) apply power to the relay terminals and see if you get continuity across the circuit you are trying to control. Usually with a VOM.
Since you are rather careless I would call a good RV repair guy to come to you and diagnose the problem
MAY BE CHEAPER IN THE LONG RUN

Google "how to diagnose RV furnace" - lots of articles/youtubes etc. Here's one that might help. https://www.rvda.org/App_Themes/RVDAMercury/docs/Sept_Oct_2014_RVTech_FINAL.pdf.

Edit: Here's an Atwood Service Manual courtesy of Bryantrv.com
http://bryantrv.com/docs2/docs/hflamefurn04.pdf

Alright - I've read pretty much everything I could on this furnace. Which is why I was even trying to hot-wire it in the first place.

Long story short - got the blower working again. Plug had a pin lose. Makes sense - when it was in the trailer it would come and go.

Problem is - still no ignition.

I had the Electrode out and fired it up - blower worked, heard clicks, sail switch closed, but no spark from electrode.

So I think at this point it's either the ignition module on the DSI board that the wire plugs into that goes directly into the electrode or the electrode itself (which looks good).

So - follow up questions if anyone has any knowledge on this:

How would I check if the electrode is working?

Or how would I check if the ignition module is working?

Just for clarification (in case I didn't explain coherently) this is the part I am talking about:



Electrode is cheap (Around 20$) but the DSI board is around 200$.

The electrode needs to be adjusted so that an arc ensues. The limit switch could cause no ignition. It can be bypassed for testing. All connections to/on the circuit board need to be solid and clean.
You could check that both solenoids of the gas valve are powered.

This document was created while I was diagnosing MY furnace.. I am told I missed one possible issue... Sadly I forget if I updated the document or not and the issue Bad connections anywhere along the line can lower voltage

When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)

*: At nearly every step the control board is involved. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.

1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid, Clogged Gas Jet
4: .1: Bad ignition circuit (high voltage) on control board. .2: Points too wide (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.

* applies to all steps by the way So does bad wire/connection.

westend wrote:
The electrode needs to be adjusted so that an arc ensues. The limit switch could cause no ignition. It can be bypassed for testing. All connections to/on the circuit board need to be solid and clean.
You could check that both solenoids of the gas valve are powered.

I adjusted the electrode already so the gap is where it needs to be.

The limit switch I didn't test yet (will be testing it shortly). How could I bypass it entirely, though? I was just going to use a meter to read voltage.

Circuit board looks good - not broken solder, no lose resistors or capacitors. It has a light on it that continues to spark when the furnace is turned on.

All connections were cleaned up and secured.

I can hear the click of the gas value opening up (at least that's what I think it is - it's coming from that direction and there isn't anything else over there that would make a noise)

So you all might think me a huge dumbass - and I honestly couldn't defend myself against that - but I 'tested' the module on the board by doing the following:

I plugged one end of the meter into the plug coming from the ignition module, and then clamped the other end on the electrode and turned the meter to DC Voltage.

I figured if I was getting a voltage reading it meant the electrode was getting voltage from the module - if it was getting voltage and not sparking tt would point to electrode.

Well - I got a voltage reading. It sometimes spiked really high (seen number as high as 1782) but was generally sitting at around 1.5 to 2.3 volts.

At this point I'm thinking what I did was just dumb and didn't tell me anything, lol.

Is there anyway to test the module on the board?

In order for me to get a new board I'd have to order it - I'm looking at around 250$+ and then a very large waiting period for it to get here - so I really want to be sure the board needs to be replaced before I do that.

Hot wired a spark plug to it and seen spark.

Basically, wire from ignition module into spark plug via clamp - seen spark.

Telling me it's electrode. Is there a possibility of ignition module not sending enough volts to spark the electrode but plenty to give a spark plug a great spark?

Going to replace electrode anyway to see.