Greetings everyone,

What are some common symptoms of a bad temperature regulator?

I ask, because my auxiliary water pump has bit the dust recently and I'm concerned that my hvac system may have been damaged as a result.

The symptoms are: all vent flaps are fully open no matter what button on the push button unit (PBU) is pressed. The PBU functions as it should, all of the buttons work. Pressing the EC turns off the compressor, hi/auto/lo buttons work as expected, and defrost defrost blows full heat ( even with a disconnected aux pump, albeit a bit weak).

I have tested each vacuum line and confirmed the vacuum system is functioning as it should (no leaks).

The climate control system is an ACIII system on an 84 380SL, but let's just pretend it's an 84 300D so I can get more eye balls on my query. Not to mention, the hvac systems seem pretty identical given that the FSM articles are practically the same and the parts interchangeable.

As always, I really appreciate the help and advice.

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-Typos courtesy of my mobile phone.

I take it all back. It's my push button unit. Total face palm. I finally found a wiring diagram that explains it all.

__________________
-Typos courtesy of my mobile phone.

If I'm not mistaken, the pre-'86 ACC has a separate module behind the glovebox that does all the actual "control" switching. The Pushbutton unit is more or less just that. The "brains" are actually in a box behind it.

The later style with square "Auto" button (same size as the fan buttons) is all integrated into one unit.

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The aux pump does not have a fuse. If it fails and draws too much current it will burn out a trace on the push button PCB. Depending where this happened on the board you may not have power to the rest of the push buttons.

If you replace the aux pump be sure to add an inline fuse at the connector to the new pump. There is a thread on this here and after repairing several damaged push button assemblies I highly recommend a fuse.

If has been suggested that an aux pump short can cause a fire. I believe this can happen but I suspect it can only happen on a car with a repaired push button unit. This is because the wire used for the repair is nearly always heavier gauge than the board trace and will generate far more heat before it melts open. In my opinion if you patch the board you must add the fuse.

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