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"So this switch is more of a safe-guard than boosting the cooling when you are in bumper to bumper traffic?"
Something like that, yes.
You have to consider how all three pressure switches operate - violet (high cut out), brown (high pressure) and grey (normal pressure). During AC operation the grey switch is normally used to turn on the radiator fan at low speed. In case of partially blocked orifice tube (which increases system pressure more than usual) the brown switch will operate (grey switch still operates but brown overrides grey at radiator fan relay). The radiator fan then turns at high speed to rapidly cool down the refrigerant to bring down pressure. However this does not translate into more cooling into the cabin. Well you can't have more cabin cooling while the orifice tube is partially blocked. In case all of these fails the violet switch will cut off the compressor. The violet switch is not wired to radiator fan. So at this time compressor will be off while the radiator fan still spins at high speed to continue bringing down pressure.
There's NO cooling boosting feature for this AC system (unlike more modern cars). Bumper to bumper traffic or setting the cabin fan to max, doesn't turn on the brown switch. If you want more cooling consider parking the car in shade before use and tint the windows. Adding one more fan in front of condenser (pusher fan) might help a bit but then you'll have to deal with the wiring setup. My observation was if you start with already hot car (parked in sun) the AC really takes time to cool down the cabin, nearly 10 minutes or more. This in my tropical climate Malaysia. I love it when it rains! The AC really shines during highway driving, town traffic not that much.
The VOV (variable orifice valve) has small moving piston prone to sticking (thus blocking refrigerant flow) in normal usage even when new. This was the problem I had when using VOV. Standard issue orifice tube only gets blocked when wear debris accumulated at its filter mesh.
"I vaguely remember hearing some high pressure leak off from the AC on an extremely hot summer day many years ago"
That could be the safety bleed valve at the back of compressor. In this case you'll have to top up the system again to replace lost refrigerant. Or it could just be the sound of pressure equalising at the orifice tube, after shutting down engine and AC. Thats normal. At quiet parking space you could hear this.
"Volvo made a service kit for corroded connectors to the three switches"
Haven't heard about this. But you could buy Bosch EV1 connector pins (at eBay for example) to replace those in the coloured connectors. Bosch EV1 type connector is standard for connecting fuel injectors and also those pressure switches. While those at eBay don't have coloured bodies or internal tabs to prevent mixing them up, you could use their internal pins (the electrical contacts). To replace the pins, pull the wire out from back of connector WHILE undoing the internal pin retaining tab within connector. A very small jeweller screwdriver might help.
Amarin.
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