Am getting both warm and cold air out of the left and center left vents when cruising at above 55 MPH. Thus, the air feels slightly warm. This is just happening out of the left two vents and not all four. Cold air is coming out of the two right vents. Seems the heat is overpowering the A/C on the left side at higher speeds, so something is opening that shouldn't be at the higher speeds.

Recently replaced the servos/diaphragms under the dash, but don't know if the problem existed before that because I wasn't getting air out of the center vents. Replaced the CCU this weekend thinking this might be the problem, but no change. So, is this a monovalve problem, or something else?

Tried a search on the topic, but didn't see anything that directly addressed this problem.

Car is an '81 300D.

Thanks,

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Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000