Good morning!
Hope you can help.

I've got a 1991 300E with 175K on it. Love it!
Recently my a/c stopped working.
When it stopped, I had just filled up with gas. The a/c was working before the fillup but stopped upon restart. I noticed the air circulation function also stopped working when the a/c stopped. Hot air is blowing out of the windshield defrost vents with no way of turning it off or decreasing the amount of airflow. All the climate control buttons did not work. It was like this all day.
Upon restart the next day, everything was working fine. Later that day it just stopped again.
This has been the pattern for the last week. Currently it hasn't worked in 3 days.
Help!

Nick

Hmmm. The symptoms don't exactly match, but I suggest unplugging the auxilliary electric water pump to see if there is any change in operation. The electric pump is activated to feed hot coolant to the heater anytime the climate control decides to warm things up a bit. On a mildly warm day it will mix in a little heat to prevent the a/c from overcooling the cabin.

The electric pumps eventually seize up/short out. This puts the climate system in a sort of protection mode to avoid damage to the electronics. The symptoms are no a/c, no fan, hot air out the defrost and side dash vents.

Unfortunately I don't know exactly where the pump is located on your particular car. Hopefully someone will chime in with that information.

- JimY