My 1984 764 had three temp sensors r/t the ACC. One for the outside temp is mounted in the intake plenum above the fan. You can get to it by removing the cowl cover...that covers the wiper motor- most likely not you problem. Then there is the one mounted in the dash behind the mini grill above the glove compartment that has a tube venturi that draws air into it and measures the inside temp. The one you are looking for is actually a temputure switch that is mounted in the heater hose and allows the system to start in auto mode after it reaches a certain temp.- this is near the coolant flow valve behind the engine near the firewall. If you hit the defroster that overrides this sensor. However in auto this sensor or switch needs to reach a certain temp for the system to start in AUTO. Mine was a V6 car but I have looked at several of these over the years and this is what I remember. One guy I knew had a problem with the "programmer" which is nothing more than a motorized vacuum control mounted behind the glovebox. He said he was able to take it apart and lube the motor and valves to fix his problem. In 1988 they came out with the ECC which was a totally different system. However it also had a delay that would wait until a certain temp was reached before the fan would come on and slowly sped up as the temp increased. This is also how your owners manual will explain the AUTO mode. I would think you could "bypass" that sensor and trick the system into thinking there is warm water...Good Luck Scot