Look either in the trunk left side behind panel or behind the kick panels in the passenger compartment
I have a 1999 blazer. The heater core clogs up about once a year from the Dexcool. Try having it (heater core) flushed and use Prestone (Extended life) instead of Texaco.
It could be a head gasket or a cracked head. Look at the exhaust manifold for each cylinder on the side that has the white smoke, the cylinder that has the leak will cause that port on the manifold to get super hot. One way to quickly identify which port is to spray some cheap black (or color of choice) paint on the exhaust manifold and fill the radiator and start the engine. The paint on the bad cylinder will burn off first.
It is a device that cycles the compressor depending on the line pressure coming out of the evaporator. Some vehicles have the switch located over on the high "condenser" side of the system.
MIGHT NEED A NEW SPEED SENSOR I posted the original question. I paid to have the symptoms diagnosed. It was actually a worn plastic gear set on the end of the speed sensor / speedometer cable and the mating gear in the transmission. The one inside the transmission requires tear-down of entire transmission... bad news.