On my '89 240, the A/C is a knob, as opposed to newer cars.

I can't quite understand why (functionally) the temp is regulated via the knob.

1.. As far as I know, there is a temp sensor running from the knob to the evap to detect how cold it is, right?

2.. Does this control the temp threshold at which the copressor kicks on? i.e. to regulate a certain amount of compression hence a certain amount or coldness to the evap?

3.. And most of all, from the 6 o'clock position to the 9 o'clock position it is RED (opposite to cold BLUE). Heat? Or is this just almost no turning on of the compressor? Why was this added to that control at all?

4.. Why did they not just put an A/C ON/OFF switch, and regulate the temp from the main temp control (heater control valve)?


If anyone understands the true reasoning behind this design, pls let me know.

Thanks,
Greg Mustang
Montreal - Ottawa
Canada