1970s 1976 ATC questions

["Cadillac Kid" Greg Surfas 15364]

Paul,
The heat load on today's vehicles are exponentially smaller than the mid sixty's Cadillacs. much less than 1/2 the exposed surface area and exponentially more and better insulation (for noise and thermal effect). The A-6 compressor was essentially developed in the early 50's, and today's units again are far more efficient.
The 20 degrees (between outlet temperature and conditioned space temperature) is essentially the benchmark for successful air "mixing". Again the idea of the Cadillac systems was to unobtrusively condition the space without undue cold drafts (remember the early 50's overhead systems).
If you were to measure the outlet air temperature of most commercial and residential AC systems while in cooling mode you would be hard pressed to find anything less than about 55 degrees F with a space temperature of 75 degrees F.
As far as pull down and outlet temperature variations, you might look into system deviations from correct function.
My 76 CdV who's system I just finished "tuning up" pulls the cabin down from a heat soak in the 105 degree temperatures we have been having lately down to a comfortable 78 degrees within 5 minutes of operation with an outlet temperature that rarely is below 45 degrees.
GregSurfas

[Chopper1942]

Many of the vehicles produced today have a normal outlet temp of mid to upper 40's.  On vehicles with a digital temp display when you turn them to as cold as the control will allow,  it will show 60 as max low temp available.

Your low pressure is spot on. The high side is high, but this depends on the incomming air temp across the condenser. The refrigerant side of the HVAC system is working OK. If there is an issue, it's on the air management side of the system.  An automatic HVAC system will not reach meat locker temps like some manual system achieve. They are desinged to maintain a comfortable temp inside the cabin.

[Big Fins]

I got very frustrated with outlet vent temps not getting below 50F on my 76 Eldorado. The entire system has been replaced with Old Air Products parts, except the evaporator. Refrigerant is R134-a with the proper compressor for that refrigerant. Parallel flow condenser, lines and a VIR upgrade.

It didn't matter the ambient temperature or humidity, 50F was the best it would do at a steady RPM. I bought a 3/4" ball valve and installed it into the heater return line to the radiator. Driving around town, now I get 47F and on a steady highway speed, 44-45F, making a convertible a meat locker.

I like it cold in the car. The Climate Control didn't. It would then start to direct the cold air into the defroster vents and the floor heater vents, resulting in a frozen right foot and moisture building up on the windshield. This is unacceptable, too. The in-car sensor sends the signal to the programmer where to direct the air. I reached through the glove box opening and disconnected the in-car sensor and placed a jumper wire in the plug.

The result is cold air out of the dash vents at the speed that I select. Not what someone thinks I will be comfortable at. Each modification is very easily reversible.

[TJ Hopland]

Which way does the water control valve work on a 76.   Vacuum means its open or closed?

["Cadillac Kid" Greg Surfas 15364]

Okay
Comparing this system to ANYTHING else is not productive. It is what it is. The VIR and EEVIR systems were a step backwards in quality and have limitations. They are VERY charge sensitive and the site glass clears about 1-1/2 pounds short of full charge. You did not say what the outdoor temperature was when you took those last gage readings but if the air was warm the pressures hint at a slightly low charge.
TJ close on vacuum.
The FSM AC section clearly states an outlet temp of 40-50 is normal for this system.
Greg Surfas