TOM WALKER wrote to ROY WITT:   
      
    RW>> So, you're just now getting around to re-charging the system, why?   
      
    RW>> In today's cars, if there is no freon in the system, the compressor   
    RW>> is locked out ot the system by the CPU and won't engage the clutch   
    RW>> at all. This affects the cooling fans and when they come on, the   
    RW>> engine runs hotter and that also affects emissions...   
      
    TW> So you are tellng us that IF the computer system sees an undercharges   
    TW> AC system the radiator fan is NO longer controled by the engine block   
    TW> temperature sensor??   
      
   That is my experience, yes.   
      
    TW> I do not believe that.   
      
   Believe what you will. When the compressor on my Z28 leaked all of the   
   freon and the compressor oil, the engine over heated because the radiator   
   fans were not engaging. Checking the engine coolant tank, it was full. The   
   engine cooled down after the vehicle began to move, but when in traffic,   
   the fans didn't engage when the temp gauge got to where they usually do   
   engage. Refilling the AC system, the fans began to work as usual.   
      
   Dunno why they build them that way, but the above is fact and not fiction.   
      
   Looking at the schematic, today's AC systems are tied to the PCM through   
   sensors on the AC refrigerant pressure sensor and evaporator tempurature   
   sensor. The PCM also controls the AC compressor relay (clutch) and an AC   
   malfunction indicator on the dash. Tracing beyond the PCM is impossible,   
   unless you have a schematic of the PCM's inner circuits. Not even factory   
   manuals have that feature. Aftermarket manuals won't even go into the AC   
   system, as the system can be dangerous for the ordinary mechanic to work   
   on. They refer you to a certified AC technician.   
      
   If you have a better explanation, I'm all ears.   
      
      
            R\%/itt   
      
      
   --- GoldED+/W32 1.1.5-31012   
    * Origin: Texas Lone-Star - Texan, American, USAian  (1:387/22)