Dometic dfds12 furnace question

[KevinK]

Hi -

I saw on youtube that the outside exhaust vent on the furnace needs to be in place, for the furnace to ignite and stay lit. Well I tested the claim, and the furnace in fact would not keep a flame when removing the exhaust plate. What is the technical reason this happens ? I do not see any sensor on the schematic that senses the heat vent in terms of a photo cell or continuity, does it have something to do with the back pressure or restriction the valve senses , etc ? Any insight appreciated.

Thanks

[Morich]

I've not studied that model very close to see but I do see it has a sail switch.
Most RV furnace have this switch in the airflow as a safety item.
First step to lighting is the fan comes on, establishes that the sail switch senses good air flow before the gas valve opens.
This keeps the propane from building up in the RV if there is not good air to move it outside! A very good thing!

So if the venting is not good, I would guess the airflow is not there and the sail switch doesn't let the gas valve open. End of cycle until the air flow is corrected.

One big thing that often happens if we are not aware, is the vent gets restricted when something like a wasp, mud dauber, or spider builds a nest in the vent if we don't add a screen to keep them out.

[CharlesMoore]

Originally Posted by Morich

I've not studied that model very close to see but I do see it has a sail switch.
Most RV furnace have this switch in the airflow as a safety item.
First step to lighting is the fan comes on, establishes that the sail switch senses good air flow before the gas valve opens.
This keeps the propane from building up in the RV if there is not good air to move it outside! A very good thing!

So if the venting is not good, I would guess the airflow is not there and the sail switch doesn't let the gas valve open. End of cycle until the air flow is corrected.

One big thing that often happens if we are not aware, is the vent gets restricted when something like a wasp, mud dauber, or spider builds a nest in the vent if we don't add a screen to keep them out.

Very good reply & my experience also.