u/Technical_Ad5375

Recently bought this used 2021 Keystone Cougar 368MBI. I tried to turn the heater on with no luck. On the inside it blows air for a few seconds, then cuts off.

Outside, the exhaust blows hot hot air for a few seconds, cuts off and then makes this high pitched noise coming from the circuit board as soon as the sail switch engages (see video).

There is a red light on the circuit board that flashes once every 3 seconds. The sticker says it means "Air flow / limit fault"

So far I have change the Sail Switch, the high limit fuse, and the circuit board, but it still does the exact same thing.

Any other ideas?