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


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 * Origin: Texas Lone-Star - Texan, American, USAian  (1:387/22)