Thanks for the replies. I am sorry that I mistakenly wrote the wrong year for my 87 560sel. 88 is for my 300ce. So here is the green sensor in my car:

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2AV19LFDZ2AV19LKHY&year=1987&make=MB&model=560-SEL-001&category=G&part=Engine+Temp.+Sensor

In my first post I said I unplugged the auxiliary fan switch. Now I realized it was the green sensor that I unplugged. So Arthur Dalton you nailed it right on the head that the sensor is shorted and unplugging it stops the auxiliary fan and allows AC compressor to start. A new green sensor is what I need.

Thanks for your swift informative replies.

Rick