I'm not a professional, but have a good bit of experience in A/C. I am very familair right now with my 92 500SL and my 92 400E is very similar. I would expect the 92 and 93 400E to be the same. From what I've seen, when the clutch slippage is sensed, the A/C locks out for a period of time. This seems to be several minutes before it tries again. Restarting will bypass that lockout. I would think that if it sensed high pressure, it might not retry at all. Do you know if it engages at all when you first start the car before it fails?

On the drier are two pressure switches. The one that is colored plastic and has pigtails should be the high pressure switch. (It is red on my 400E and is green on my SL.) If it were mine, I would consider that switch to possibly be faulty. I think you have to evacuate the system to change it.

I believe that a clogged receiver/drier or expansion valve could cause high pressure. The expansion valve should not care about the ambient temperature. Could the drier clog when hot? Not very likely, I would think.

Is "A/C Lockout" the only code it throws up? I think there is a separate code for high pressure.

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)