I have been watching my a/c slowly go crazy over the past week in my 1991 300D. I know my compressor is good and the blower fan was recently replaced. All worked well and then a short time later, the whole thing went insane. Here are the symptoms (assume temp dial is always at 75):

1) With a/c selected (middle button) at moderate temps (mid-upper 70s), a/c blows correctly out side vents and lightly in center (I think the center control pod may be bad, but lets hold that thought.) Fan speed seems sufficient and will increase if I lower temp dial.

2) When temps get near 80s, the system will suddenly shut off center vents redirecting to windshield, and blows cool (not cold) air on outside vents and to windshield - feels like cold a/c air has been reduced and there is more outside air. Fan reduces speed. Higher temps exhibit same behavior - fan will not increase speed as temp dial is moved - I can get it to turn on heat thought if I spin dial up high enough (do not try this with family in car on 90 degree day )

3) If I choose the switch just left of the middle one, no real change from symptom 2 above. Seems like middle button is acting like one to its left, but only during temps of 80+

Here is why I think my climate control has gone mad (it works on economy):

3) If I choose the economy switch (just right of center) with moderate to hot temps outside (anything above mid 70s) the fan kicks in high with ridiculous amount of air on side vents, windshield vents are shut off and there is some air movement coming from middle vent, but nowhere near the volume at the sides. Apart from a possible "middle vent pod" issue, this scenario appears to have everything functioning correctly (AFAIK.) Fan speed will adjust as temperature dial is moved (fan increases as dial temp moves away from current temperature.)

4) Generally, high fan switch doesn't produce the fastest fan speed - it is decent but not like the wind turbine effect when my economy switch is pressed and its in a hurry to catch up.

Based on this, does a faulty climate control or something other than "just pods" seem reasonable? Any ideas? Is there any other "control" for the system apart from the in-dash unit with the buttons?

I pulled out the climate control module, disassembled it, cleaned what I could and put it back in - no real change. Did notice some dark discoloration below a transistor on the circuit board (kind of a crusty, brown coating) - I am thinking the transistor might have cooked itself.

I am just wondering if I should pony up for the control module before hunting down the pods and the possible overhaul with the dash removal, etc. I haven't tested the pods with a vacuum pump where the 7? lines meet near the glove box - will do that in near future. Trying to decide on control module at the moment.

Thanks,
ThirstyValves