HydraFlame 8500-II Issues

The computer with the file on it is .. Dead battery. Just now.. This one does not have storage space to speak of.

When the T-Stat calls for HEAT it talks to the mother board on the furnace, and yes it's a MOTHER often as not, also about 250 dollars to replace (OEM) or half that if you buy from Dinosaur Boards and better quality in this electroncs Trained person's opinion. More on that later.

The T-Stat talks to the control (mother) board and calls for HEAT
The board then starts the fan.. Waits a bit and when the fan is up to speed it opens the gas valve and makes with the sparks to ignight.

Since we are not getting to this point I'll stop here

You can download the wiring diagram for the unit from Atwood (I DID) and then you will find....

On the Circuit board connector there are two blue wires.. Should show 12 volt (referenced to ground) on one of 'em.. the other one is the T-Stat lead and if the T-Stat is calling for heat it too will show 12 volts.

Then you need to find the wires to the blower.. they are rather heavy. measure voltage on those wires.. Turn the SWITCH atop the blower (Oh, it is also a circuit breaker) OFF, wait 5 seconds and back on.. IF the T-stat is calling for heat you should see 12 volt on the blower leads within 1 second.. IF YOU DO and the motor is not running.. YOu have narrrowed the problem to the motor or the motor leads

If you do not. then get a new Dino Board.. DOUBLE CHECK THIS but I think it's a fan-50 for that furnace.. NOT 100% sure of that though so go to the factory web site and double check

American RV in California is where I got my Dino Board... .Back in 2012. Still working fine.

It says you can use any thermostat "suitable for 12 or 24v systems" so IMO be a good idea to replace it.

I have had to replace the water heater propane switch that has that red light on it in the 5er. Those switches wear out but can work sometimes first before not working at all. Hard to tell if it the switch or the actual ignition etc. Switch is easy fix. Same as the other thing, jumper the wires to it to see if the thing then works.

The MH, has the monitor panel on the range hood. It had 12v ok for the water pump and light, but no lights for the levels. Needed a new "momentary" rocker switch in the panel. Easy to pry the panel out from the range hood front to get at it all. It has a level light for the big propane tank, so we'll see if it is telling the truth about that level. No red/green indicator like before with the two 30lb tanks in the 5er.

The MH came with a 6300 converter. I did the fuse panel jumper trick and by-passed the 6300 converter part to use a newer type deck mount converter that does not need a battery to act as a filter.

I have not got the television antenna working yet. It is a sort of weird batwing but has no amp in it--the amp is in the wall panel. The panel has 12v ok but the amp seems dead. Anyway, I can see a Jack going in there soon. :)

Well it works again.
After much trouble-shooting and verifying that everything in the back of the furnace worked, I took the stat off the wall (the one he twisted the wires together from...) and put a jumper between the two wires.
It fired right up.

Then he told me the water heater quit again.
Ugh.


Thanks again for all your help.

Thanks OB. As usual your knowledge and advice are priceless.

Scott.......

The components on fan cover are:
*Far Left ------ON/OFF Switch--Circuit Breaker
(12V DC POS comes from Fuse on DC Dist Panel----to On/Off CB --to 'timed delay relay' --- to motor)

*Far Right -----'timed delay relay'
(coil inside gets hot allowing DC to start motor for purge cycle....then later allows motor to run cool down cycle until coil cools of stopping DC to motor)

*Center ------Ground block

***White wires going thru grommet inside motor cover go to the Sail Switch

Pg 11 for 85-ii wiring schematic

The owner's manual I have for our 8500 II might be on-line but all I can find is for the IV. I didn't check to see if it is similar.

Yes, check inside the thermostat. The off switch matters! However if the furnace was working and then didn't, it could be several things. A fuse, a circuit breaker, the blower relay, etc.

I can't tell which thing is which, but some of the things don't come on till others do so I don't think a meter can tell much if the voltages are right unless it is running? I don't know.

The thermostat gets the blower relay going after a time delay up to a minute, and that gets the sail switch to close once there is enough blow, and that energizes the DSI Board, which has a 20 second delay for a furnace purge, then the gas valve opens, and an ignition spark. If no flame after a few seconds of sparking, the DSI Board shuts off the gas valve. There is a limit switch to shut it down if it all gets too hot --like from an air circulation restriction (like wasp nests in the exhaust?).

BFL13 wrote:
Note the thermostat can have a tiny on/off switch at the bottom besides just turning up the heat lever.

It does have that switch - I couldn't even read the writing on it!
But he removed it and twisted the wires together, or at least he said he did. He's had at least three tramatic brain injuries and often has a hard time thinking straight about anything technical.
Maybe I should double check the stat's operation.

I'm curious what the second and third things with wires on the side of the blower housing are and how to test them.

Note the thermostat can have a tiny on/off switch at the bottom besides just turning up the heat lever.

BFL13 wrote:
The 1991 MH we just got had that issue where it seemed that it ought to run since the usual checks came out ok, but it would not. I eventually found the external exhaust (bottom right in photo) was full of wasp nest combs and dead and half dead wasps. Poked it all out with a long rod and all of a sudden the whole thing started to work. Then the strong exhaust blew out some more wasp stuff that I had broken up with the rod.

Thanks for the tip - I'll check that out tomorrow!

Scott

The 1991 MH we just got had that issue where it seemed that it ought to run since the usual checks came out ok, but it would not. I eventually found the external exhaust (bottom right in photo) was full of wasp nest combs and dead and half dead wasps. Poked it all out with a long rod and all of a sudden the whole thing started to work. Then the strong exhaust blew out some more wasp stuff that I had broken up with the rod.