1996 A/C blows cold with no high side pressure

Hi all, so I recently replaced my A/C condenser, evaporator, liquid line and clutch cycling switch on my 1996 gt, as well as o-rings on all mentioned components.

Brought the car to a shop to have it professionally refilled and it now blows cold. However, the vent temp fluctuates while I'm driving up as high as 66 degrees, so I thought there might be a problem. I hooked up my manifold gauges and when the system is off it equalizes to about 80 psi on both sides. Once I turn the car and A/C on the low side goes to about 30 psi with the compressor running and the high side stays right at 75. In fact, the high side slowly drops in pressure as the system runs.

The strangest thing is that the A/C still works, I get about 45-50 F in the cabin while idling and it's about 80 F outside right now. I thought the system could not function with these kinds of pressures. Any ideas what could be going on here? Any input is appreciated.

Thanks for the reply, I forgot to mention that these are brand new Schrader valves. Also when I attach the high side hose I hear the valve hiss for a split second and it reads the pressure (about 80 psi static, same as low side) which leads me to believe that the valve is functioning properly. However once I start the system the high side doesn't go up at all and very slowly drops. Again the strangest part is that the A/C is still working at least relatively well. It makes no sense to me.