Atwood Furnace - Blower Won't Start

[SteveZ494]

I have a 2006 Bounder with a Atwood 8535-IV-DCLP furnace.

Last fall, the fan would come on, but no heat would be generated. Being I was putting it away for the season, I figured I would dive into it when spring arrived.

Spring has arrived and I dove into it. However now the fan won't start.
Troubleshooted it down to the circuit board. Had the board tested and confirmed it was bad. Installed brand new Dinoaur board but blower still won't start.

Confirmed 12.9v to thermostat and furnace.
12V directly to blower motor confirms blower is good.
Confirmed that furnace switch/breaker is good.
All breakers and fuses appear ok.
Do not see any fan relay to test.

Figured I had it tracked down to a bad thermostat, so I bypassed the thermostat at the furnace, waited 30 to 60 seconds but fan still does not come on.

So now my level of "some knowledge is dangerous" is maxed out and I'm perplexed on where to look next.

Green LED on Dinosaur board is steady on. Is this normal or indicating a fault?

I obviously need to get the fan initiated to determine if the original problem of the furnace not igniting will still exist or not. (Maybe the new board will have fixed this original problem..........maybe not.) <sigh>

Thanks in advance for any help!

[powercat_ras]

I would see if you can read 12 volts coming from the board to the blower motor, and see if you can confirm the blower motor to ground is good.

Green steady on is indicating the board is trying to spin up the blower motor, and is waiting for the sail switch to indicate that the blower is moving enough air to make it safe to start the ignitor sparking and turn on propane. When it starts trying to do that the light will flash or flicker and you will hear the spark.

[Old-Biscuit]

Did you use a Dino 'UIB S' circuit board for replacement?

LED Green ON...all good
LED GREEN OFF----Limit switch, Sail switch or 5A fuse on board
LED RED ...gas valve open

S/B a timed delay relay.......
Red wire from the local On/Off CB on furnace frame goes to it
Blue wire from t-stat goes to it
RED wire from Relay goes to motor
Yellow wire from Relay goes to ground

See pg 10 (blower control board AND Time Delay 85-IV
http://bryantrv.com/docs2/docs/hflamefurn04.pdf



Unless old circuit board was changed to a 'retro kit' board (with fan control on board)
Atwood #38676 (no Dino Board)

[powercat_ras]

One more thing ... I assume you are able to easily spin the blower wheel by hand, if not you may have to pull the furnace out and resolve why, a common issue is insects like wasps nesting in the burner air intake port side of the blower. The furnace blower has two sides separated by a divider, a long side that blows inside air and a short side that moves the air direct heated by the burner flame thru a heat exchanger and out the exhaust port.

[SteveZ494]

Thank you for the replies. I will attempt to address the recommendations:

The blower motor does run when I apply 12V to the terminal. It runs normally. I believe that would indicate an intact ground and that it is free from any (insect) obstructions.

I am using the Fan 50 Plus Pins board with the jumpers left in their factory positions.

I am not visualizing a (time delay) relay unless it's mounted somewhere BEHIND the blower motor. Looking from the front of the furnace, I'm not seeing such. It appears that not all furnaces have such a relay? Is that correct?

[Gary RVRoamer]

The time delay could be built into the circuit board, rather than a separate component. I think that is the way newer furnaces are designed.

According to the Fan 50 plus instructions, the green LED will be on without the fan running IF the sail switch is stuck in the closed position.

http://www.dinosaurelectronics.com/I...n50PP_inst.pdf

[SteveZ494]

Just spoke with Dinosaur tech guy. He IMMEDIATELY stated that the steady green LED indicates a stuck sail switch. He was certain!

Now the search on how to get AT that sail switch! Hopefully a blow torch or the Jaws of Life will not be necessary. <grin>

I'll update my progress.

Thanks again.

[powercat_ras]

Atwood Sail Switch Troubleshooting

There are some great youtube videos of Atwood furnace guts out of RV being bench tested, I posted one link above. This should help you visualize where the sail switch is. I think you can see it and do some troubleshooting without taking the furnace guts out of the RV.

[SteveZ494]

The sail swithc was actually mounted to the front plastic housing covering the blower cage fan. Four screws and BOOM! There it was!

Switch was normally open (as it should be) but wouldn't close when activated.
Wire brushed the contacts and shot some contact cleaner in the switch. That resulted in the switch now operating. (Think the results was more from the spraying the contact cleaner than the wire brushing the contacts.)

Put everything back together and it's working like a champ!

A hearty THANK YOU to those that responded! I hope can can return the favor to the group.

Happy Camping to all!