on the 103 there is tsb re idle with a/c on/off. this was
corrected by my mb dealership sometime ago free of
charge (89 300e). i was told that the rpm will dip
when you switch the a/c on, but will rise up to normal
level (600 - 700) immediately afterwards.

would suggest for you to visit your local dealership,
also reexamine your ac compressor for electrical draw.
is universal motors still around?

__________________
joel

Prayers bring forth enlightenment.