77Monaco
Member
I hope this is the right for this but I'm looking to replace the furnace and don't know what to replace it with.
Atwood 8535-II furnace
- Thread starter 77Monaco
- Start date
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Gary RV_Wizard
Site Team
Why replace it? Just about everything is repairable and parts are readily available. Or are you looking for some alternative form of heating, e.g. electric or diesel?
If you feel it is truly a goner, why not a newer 8535? Dometic/Atwood has renamed all the previous Atwood models, but they are essentially unchanged. The 8535 is 35k btus, what Dometic now calls a "large furnace". The two-speed versions are really nice if you want the top-line features - on "low" they are quiet yet still produce good heat and keep an RV comfortable in most weather.
If you feel it is truly a goner, why not a newer 8535? Dometic/Atwood has renamed all the previous Atwood models, but they are essentially unchanged. The 8535 is 35k btus, what Dometic now calls a "large furnace". The two-speed versions are really nice if you want the top-line features - on "low" they are quiet yet still produce good heat and keep an RV comfortable in most weather.
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77Monaco
Member
Thanks for the input. So far the thermal switch, igniter board, and rewired according to the updated wiring bypassing the relay. Nothing goes as if there is no power going to the board. I'm frustrated.
Old_Crow
Well-known member
A few years back I had the gas valve go on my 8535. When I got the new valve, everything was so corroded I couldn't get it apart without damaging it. Ended up buying a good used unit from Colaw Salvage in Missouri for 1/2 of what they wanted for a new one.
Kirk
Well-known member
What sort of voltage readings are you getting? What troubleshooting have you done?
Atwood 8535 furnace service manual
77Monaco
Member
When I bought the motor home the furnace was missing the circuit board.
I had my son in law( ase mechanic) put in a new one. The new bypassed the relay which was mickey moused in to the wiring. He wired the new board according to instructions but seemingly no power. He could not find where the problem is. There is power to the board but intermitant power every else.
I had my son in law( ase mechanic) put in a new one. The new bypassed the relay which was mickey moused in to the wiring. He wired the new board according to instructions but seemingly no power. He could not find where the problem is. There is power to the board but intermitant power every else.
Lou Schneider
Site Team
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- Mar 14, 2005
- Posts
- 13,249
There's a precise startup sequence in the service manual. In a nutshell, closing the thermostat contacts is supposed to start the fan motor. Nothing else happens until the fan provides sufficient airflow to close the sail switch contacts, then after a time delay the ignitor starts sparking and the board commands the gas valve to open.
If you have a combined heating and air conditioning thermostat, the thermostat communicates with an interface chassis inside the air conditioner plenum (on the ceiling), which provides the contact closure to the furnace control board. Try jumpering the thermostat input directly at the furnace to isolate the problem area.
If you have a combined heating and air conditioning thermostat, the thermostat communicates with an interface chassis inside the air conditioner plenum (on the ceiling), which provides the contact closure to the furnace control board. Try jumpering the thermostat input directly at the furnace to isolate the problem area.
77Monaco
Member
The other issue is there are two thermostats and two air conditioners.
Kirk
Well-known member
If there is only 1 furnace then the front thermostat controls it and the paired air conditioner and the rear thermostat only controls the air conditioner. That is not unusual. But the front thermostat still passes it's signal to a control circuit board that is located in the air conditioner, as Lou has suggested.
77Monaco
Member
Sorry I took so long to reply. After all this I am taking the furnace out and taking it to a shop. It seems around here techs don't want to travel to an old rv to work on.
Kirk
Well-known member
The key thing to remember is that if your problem is caused by a lack of signal from the thermostat, the issue could be either the thermostat, or it could be in the control circuitry in the associated air conditioner.
