The compressor micro switch installs as shown here on a '67-'68 Mustang. Mark and drill a 1/8-inch screw hole. When the heater controls are moved to the "off" position, it closes the micro switch to begin current flow to the compressor clutch. With the fan off, there's no compressor-clutch engagement. If box temperature is below engagement value, then no compressor-clutch engagement will occur. And finally, if the pressure switch is open due to high or low pressure, no cigar there either. All switches in the chain must be closed for clutch engagement. Old Air Products also provides the fan switch necessary for Hurricane operation. This is a three-speed switch that, ironically, is the same basic design found in classic Fords. It has a three-pin plug that ties it to the blower motor.