Atwood furnace low voltage issue

[Jim McGarvie]

We've had some instances of our Atwood 8535-IV-DCLP not lighting when the batteries have been low. The blower runs, I can hear the gas valve opening and I think I hear the igniter clicking, but no burner light. I understand the furnace won't function properly at very low battery voltage, but I thought it would work down to maybe 11.0V or even lower, but our issue was with a battery voltage of 12.0 and 12.1 volts. Anything above that it works fine.

My question is this: What component of the furnace is voltage-critical, that I should try replacing? Or might the problem be unrelated to voltage and just a coincidence?

Thanks.

Jim

[Walker]

I was having similar problems with mine.  Mine had some t-tap connections that were not in the the best of shape(loose crimps and corrosion).   I replaced them and a few of the spade connectors. That fixed it for me.

[Jim McGarvie]

4 hours ago, Walker said:

I was having similar problems with mine.  Mine had some t-tap connections that were not in the the best of shape(loose crimps and corrosion).   I replaced them and a few of the spade connectors. That fixed it for me.

Thanks Matt. I cleaned up all of our connections, but haven't had the same low voltage situation since. Hopefully that fixed it for us as well.

[Harvey Babb]

I had this happen when the gas valve was not opening. It did "click", but sounded muted and was not actually delivering gas. This problem caused me many nights waking to a freezing bedroom and resulted in me getting to know the furnace WAY better than I'd like!

While it's working right listen to the operation carefully so you know what a normal start sounds like and see if you can detect a difference when it acts up.

You might try standing by while its trying to start and giving the gas valve a whack with a screwdriver handle.

What I learned standing in the cold darkness was that the sequence of operation programmed into the control board goes as like this:

Thermostat wants heat so supplies control power to the blower relay, the overheat shutdown switch and the sail switch.

After a few seconds (up to ten or more if it's cold) the blower relay clicks and starts the blower.

Almost immediately the sail switch detects air flow and feeds control power to the control board.

The control board starts the purge timer while the blower clears out any gas present and waits until the purge timer is satisfied.

When the purge timer is satisfied the abort timer is started, the gas valve is powered "On" and the spark igniter starts clicking.

The burner ignites with a slight "whump" and flame can be heard.

The flame detector circuit detects current flowing through the flame probe to the flame proving it's burning, and the spark igniter turns off.

(If no flame is detected before the abort timer times out, the gas valve is turned off and the control drops back to purging again. It will continue to cycle through "Purge, Gas On, Ignite" until it successfully lights or you get tired of it blowing cold air and turn it off.)

(If there is insufficient air moving around the firebox the overheat shutdown switch will turn off power to the control board until the temperature drops and then drop back to purging again. It will continue to cycle the burner off and on for as long as it keeps overheating.)

When temperature in the coach satisfies the thermostat control voltage turns off, closing the gas valve.

After a period of 10 or more seconds the blower relay drops out and stops the blower.

Note that the blower motor turns TWO blowers: the big one for circulating cabin air around the firebox and a small one that supplies combustion air to the burner.

 

 

 

[TimSpencer]

Low voltage could cause many issues. Including not keeping gas valve solenoid open, poor controller operations and poor draft motor and or blower motor performance. The controller is going to look for feedback from safeties and if the voltage is low it can perceive that as a safety being open. This is why bad or loose connections can cause issues as well.