A/C high speed fan switch..which one
 

Who knows a thing or two about air conditioning? Last year I broke down and had a new compressor installed, the a/c had not been operational in probably 7 years. Anyways..when I turn on the a/c, runs great by the way..cold air blows great....isn't the high speed fan supposed to come on?..or does it come on by pressure in the system or by temperature ? The reason I ask is because, the high speed fan will come on about 10 seconds after I hit the a/c switch..and then it goes off and on, off and on very internittantly..until..if I raise the rpms it seems to stay on and running fine..mind you it does this..first start in the morning.when the engine is cold So there are two switches connected to the rec/drier..I'm figuring one of those is just bad from it not being used in 7-8 years..and probably gummed up..before I had the system operational again..SO WHICH ONE CONTROLS THE OPERATION OF THE HIGH SPEED FAN ?? The top one or the lower one..I've disconnected the wires and made sure contacts are clean. could the freon charge be low and causing this? My mechanic said the high speed fan would not come on at all if the freon was low.

btw..87 944 n/a..141,000 miles and runs strong

Fans should run in slow speed when you turn on a/c. Then when in traffic, and high side pressure goes up beyond maybe 250 psi, the fans run in high speed. If it is not running in slow speed, your fan slow speed resistors could be fried or open.
Hope that helps.