lPlB, Phil Here. I had the same problem with my Sweet 92 SL, For me it was a stupid simple thing. On my Dash I have a " Roller " temperature switch, If I roll it down beyond the " Blue Limit" and feel a "Click" your compressor will not come on. You can then run your system on Economy.
I think this is the way the car was built. It worked for me.

1992 Sweet 500SL Phil Justice