190e A/C - cold in the middle - warm on the ends?

[2benzman]

My 190e 2.6 is intermittently blowing warm air from the outside vents (driver and passenger) with the A/C on. I'm still using R-12, took it to a shop and had it tested. It was a little low (~10 oz.), but topped it up and seems to work well - no bubbles in the site glass. Problem still there.

I read some threads about the monovalve. Is this the valve that is between the Aux pump and the heater core on the passenger side? Has an inlet/outlet and a vaccuum line on top?

As a diagnostic, can I shut off the Aux pump and block this line?

Any other diags would be helpful. Sometimes the A/C blows ice cold.