Daughter brings home car w/tale of woe, no a/c after winter.

Basic troubleshoot shows compressor not engaging.
Seems to have a charge but I do not have proper gauges.
Do not see where fuse is for compressor, not listed on any of the 3 fuse blocks.
I assume it is in-line somewhere?
EC button is lit and will not go out when button is pressed, bad switch or more ominous?
Compressor turns by hand.

Just for giggles, I checked duo-valve. Seems fine, no hang ups.

Anything else I can check before I take to a shop?
(A/C is about the only thing I farm out, hate doing it but no tools/equipment)

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1999 E320 (gave to daughter) 250K
1994 F150 (may be the end of its road) 240K
1989 560 SL (Reassembly after paint job) 160K
1986 560 SL (deceased., gave it's life protecting my wife)
1988 300 TE (departed)
1994 945T (still running strong with an upgraded cam) 349K
1986 242Ti (deceased)
1968 GT500KR (under restoration)