Odd A/C Problem

It has been awhile since I have messed with AC, but if I remember right there is a schrader valve like the type used on a tire valve stem under that switch. So you shouldn't have to release all the system pressure in order to remove and replace the switch. If you unscrew the switch all the way and there is still freon coming out, then yeah you'd have to replace the schrader. At that point I would want the system to be vacuumed down and recharged professionally.

 

This is an old post but having just gone through my 1996 Tacoma's leaking AC system, I can provide answers.
1. There is a blowoff valve located on the compressor. It is not sold separately by Toyota; you must buy the entire upper manifold for $206.00 to get a new one.
2. If the system is spewing refrigerant from the blowoff valve while the A/C is running, the likely culprit is a blocked expansion valve; it is located next to the evaporator coil inside the airbox behind the glove box. It could be blocked with debris or even ice if the system has been open to the air or moisture.
3. The pressure switch is located next to the expansion valve.
4. Always evacuate the system prior to charging, IMHO. An old refrigerator compressor will do the job well enough. Been using one for 30 years.
For my Tacoma, the evaporator coil was leaking. I got the entire airbox from a self-serve wrecking yard (Pick-N-Pull $40.00) from a 1998 Tacoma which is exactly the same as the 1996 and it works perfectly.