No hot air coming from the center console vent?

1996 MERCEDES BENZ S320
286,838 MILES • 3.2L • 6 CYL • 4WD • AUTOMATIC
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SUHAILKADER
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replace entire heater assembly, but hot air does not come out of center dashboard heater vent. left and right vents a working but hot air flow is not optimum level.
Work history: bypassed heater control valve and directly connected hose to the water pump. The other 2 hoses are closed by using stopper.

Looking forward for some suggestions.
thank you
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Jan 19, 2024 at 11:18 PM
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STRAILER
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Are you getting vacuum to the main air flap when the HVAC is in the face vent setting? Also, there is a main air flap upgrade. If you are not getting vacuum to the main air flap but you have vacuum to the other flaps, then the main HVAC controller has gone out or the line has a break in it. Here are diagrams of the system so you can check it out. Make sure you have vacuum to the main control head as well. Check out the images (below). Please upload pictures or videos in your response to the problem so we can see what's going on.
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Jan 21, 2024 at 9:59 AM