[rapsag]

I have a 73 drive train (Camaro 350) with a Vintage Air a/c system that was installed in 1990. Recently had a relay meltdown with shorting of the hot wire into the ignition. After getting all that straightened out, which included a new wiring harness from Vintage Air (with an inline circuit breaker fuse on the hot side), I noted that there is no binary switch in the system. It has a reconditioned Harrison type compressor, and all joints are barb and crimp. I have a drier that has a sight window.
Question:
1. Should I install a binary switch? My electric fan is hand operated from the dash, which I am used to, so I don't need the trinary type switch.

2. Assuming that I install the binary switch,(there is low residual of R12 that I will have to deal with) and I cut the line and install quickly, is there any need to pull a vacuum on the system before I charge back up with Freeze 12?

3. Where is the best place to place the switch?

rap

[rapsag]

First the unit is now not cooling and with the compressor on there is lots of bubling in the sight glass on the drier. So I assumed that there had been a leak. With the engine off, after waiting overnight, I took the pressure on the low side (large hose?) and it was 75, way up in the danger zone. How can this be? I need to know these things before I venture into trying to put the binary valve in and loading up the system. This unit had not been used for 15 years after installation (no charge). It was inspected, and charged up in St. Louis by a local a/c shop according to the seller. It has a rebuilt Harrison type compressor which has a sticker that states R12 4.1 lbs. The valves are the old type of R12 valves. It ran cold for the past two months without a problem until about a week before the relay fried. I have not confirmed that the tech used actual R12.
Concerned about why the resting pressure is so high? rap