A/C and heater inoperative

1990 MERCEDES BENZ 420SEL
210,126 MILES • V8 • 2WD • AUTOMATIC
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LEEBK
  • MEMBER
  • 2 POSTS
I have no heat or A/C. I have replaced the mono valve, condenser, compressor and climate control, and nothing has changed. What else could be wrong?
Jul 17, 2018 at 10:54 AM
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STRAILER
  • CERTIFIED EXPERT
  • 53,854 POSTS
Can you explain? So you do not have any air coming out or the cold and hot are not working?

Please let us know, Ken
Jul 18, 2018 at 5:57 PM
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LEEBK
  • MEMBER
  • 2 POSTS
I have no heat or cold air. The fan works and is passing air through the vents, but the air will not change temperature.
Jul 18, 2018 at 6:45 PM
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STRAILER
  • CERTIFIED EXPERT
  • 53,854 POSTS
This system is vacuum operated. Here are the diagrams to show you how it works it sounds like you have a leak which is not holding vacuum and not moving the doors. Also, check under the hood to make sure the vacuum feed line is intact.

Check out the diagrams (below). Please let us know what you find.

Cheers, Ken
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Jul 19, 2018 at 10:49 AM