The settings should be the same before switching the AC on.

When you do switch it on you should be getting the values given here for high and low lines.

Whats the temperature inside of the cabin?

A blocked/broken condenser or bad reciver should be considered.

Did he put a BLACK light on the system??

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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

The temperature inside the car was above 90. When I say hot air is blowing out of the vents, I mean HOT air coming out. Therefore, I also suspect the monovalve is not working properly...

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J.H.
'86 300E