Yeah you can do that pretty easy. Best way to avoid it is to pull off the knob, pop off the cover with a small screwdriver and take out the nut. You just have to leave that silly thing floating around away from the center console. There is a way to hook up a DPDT switch until you get a donor part. You put the two Red White on one side, and the greens on the other. Flip the switch and you send the 12 volts out the relay and compressor. Running it that way will freeze up the condenser it left on long enough. But for trouble shooting works like a champ.

That little tube was filled with r12 and controls the AC switch, that was the little hiss. It is to keep from freezing up the condenser coil and can not be fixed. Held onto the tubing before the expansion valve by a metal clip. You can get one off almost any donor up until they changed over to the variable orifice in the 90's. You will find that a lot of them are already busted or covered in green crud. Broke a couple of them off trying to get them loose from the tubing down there. Took a battery reciprocating saw in with me to the PUP and just cut out the tubing and left the tube on the old section of pipe. Took it loose at the house so care could be used. Put in on the pipes with nylon tie wraps and lubed up the knob. Been working like a champ for a couple of years now.

Good Luck,

PT