Quote:
Originally Posted by daw_two
Which car? I would say......it depends.
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100%.
In an 80s-00s MB: a valve opens to let hot coolant through the heater core. Air always flows through the heater core.
In an 85+ VW: hot coolant always flows through the heater core. A blend door directs air to and from the heater core to control temp.
In a 92 Dodge Ram: hot coolant normally flows through the heater core. A blend door directs air to and from the heater core to control temp. A vacuum valve shuts off the coolant flow when Max AC is selected.
The blend door system has one advantage: You can change the temp very quickly from full cold, to full hot, back to full cold. In the MB system you have to wait for the heater core to warm up (this happens quickly), then cool back off again (this takes longer).
-J