My understanding is that the VSV (Vacuum Switching Valve) handle heavy
acceleration cut off of compressor. Ever see old cars of the 40's with
vacuum windshield wipers where the faster you accelerated the slower the
wipers went? A vacuum completes the circuit and compressor engages and low
vacuum (heavy acceleration) opens it disengaging the compressor.
The VSV that is connected with the A/C system is to boost the idle speed via the
idle-up valve. It works in conjunction with the A/C amplifier to keep the
engine from idling at too low a speed and thereby turning the compressor at too
low a speed to work
properly. Since my A/C compressor is disconnected right now, I was able to
utilize the A/C idle-up VSV to effect a push button fast idle setup. With the
A/C clutch disconnected and a jumper in the low pressure switch, hitting the A/C
button will cause
the VSV to open and let vacuum flow to the idle-up valve and the idle rises as
dictated by the setting of the whte knob atop the idle-up valve.
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