Had a problem yesterday on the drive to Houston where the A/C suddenly started blowing hot. Finally cooled down but the center vents weren't putting out air. (I'd also had some other weird things going on with it the last few weeks.) Under dash pods had recently been replaced. Last night we swapped the CCU and problem still existed. Luckily my son saw where the cannon plug to the A/C amp above the glove box had become disconnected. Plugged it back in and A/C now working like a champ.

So, your problem could be something as simple as what we ran across. I suppose the A/C amp might also be bad. However, I'm not technically sharp enough to diagnose.

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