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Webasto Circ Pump-Liberty
Why does the Webasto circulation pump run 100% of the time in a Liberty? The coach has a DBW 2020 Webasto. The heating system wiring drawing shows the pump wired to terminals 1 & 2 of the A socket of the controller. The timing diagrams in the service manual indicate this circ pump output shuts down after the completion of the cool down cycle. Yet many post’s confirm Liberty circ pumps run all the time when the power switch is on.
Roger
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3 Replies
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Yep, Liberty has the pump running full time, I’ve had 2 of them. My Marathon shuts down the pump during the cycle. Your inverter bay cooling fans run full time as well as opposed to being on a thermostat. There are differences in the way Converters do things, but they all work.
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I’m not defending or criticizing the Liberty choice of running the Webasto circulating pump full time, but I am wondering if there are any benefits or drawbacks.
A burner does not burn full time because when the coolant is at a certain temperature it shuts down until coolant temperature drops to the kick in point. If every time the burner shut off the circulating pump shut off, the heat exchanger coolant would get very cool very fast because if the area needed heat that heat exchanger fan would be running. Before more heat came out of the heat exchanger the burner would have to kick back on and the coolant would have to replace the now cold coolant in the heat exchanger. That’s a plus for the continuous running.
An alternative would be to only have circulating pumps operate until the house or engine block heat is satisfied. As long as any thermostat in the house or bay needed heat the pump would run, but shut off when no heat is required. That would work also, but might involve a more complex control system. Maybe that is how Marathon does it.
I have learned that most of the systems converters design are well thought out and they have given a lot of thought to various conditions. Remember, our coaches are not much more than a great number of compromises about how to use space, how to design systems and what things have to be sacrificed to get the best combination of reliability, operating characteristics and quality.
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I agree with both Tom & Jon. The real discrepancy was in the Webasto service manual. Manual suggests that the ECU recirc pump output terminals are switched to correlate to the complete burn cycle as shown in the timing diagram. Tech support confirmed that the recirc pump terminals are simply a pass thru of the power switch. No cycling of the pump. Hence the pump is on when ever the power switch is on.
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