about 5 years ago my climate control unit didn't change modes so i took a shot in the dark and replaced it with a rebuild unit and it worked. the other day i went to switch modes heard a big clunk and nothing. now it no longer switches modes, just fan speeds.

my question is how do i troubleshoot this? did the rebuild climate control unit fail? is it some other door or something stuck/broken?

Thanks

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1987 420 SEL | 87k miles
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Hello - take a look at the link below to an older thread where this is discussed. Hope this helps and best of luck!

Something wrong with w126 climate control system?

ugh... my takeaway from that thread is...replace everything.

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1987 420 SEL | 87k miles
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I think we need a better picture of whats not working on the system.

Blower motor can change speeds.
Does the temperature wheel have any effect on the system's output air temp?
When you press the button on the push button unit do ANY of the vents outputs change?

The HVAC system uses vacuum pods to adjust dampeners. The pods are controlled electrically through the push button unit but the actual moving of the dampeners is carried out by vacuum. If the vacuum supply is no longer connector or is super leaky then that would easily defeat the whole system. You might have this problem.

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UPDATED

- blower speeds change with buttons
- temperature wheel has no effect on system output air temp (always warm)
- pushing buttons to change vent output, i get defroster mode and the white up white down arrows mode where air comes out everywhere except defroster.

If i just focus on the temp wheel issue. what should i be looking for? thx

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1987 420 SEL | 87k miles
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The problem was a blown out rubber diaphragm inside the Vacuum Element - Main Air Flap Control (the one on the right side when looking at it from the passenger seat. You can access all three of these vacuum valves after removing the glove box insert.

Once you remove the valves, either disassemble them and inspect OR plug the holes and see if they hold vacuum after pulling / pushing the rod.

Ordered Part #: 000-800-57-75-M22 from Pelican Parts.

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1987 420 SEL | 87k miles
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