If the compressor was running "wide open" it would suck the low side down below 30 psi quickly. Back the car out of the garage and clean the condenser. Use a strong surfactant like simple green or zep orange. Spray a lot of it deep in to the fins & let it soak for a few minutes. Then f...

How significant was the drop with a wet condenser?

Generally this points to an airflow issue on the condenser.

Yep, no different than running dual evaporators in a Suburban with rear A/C.

Does your current evaporator use a TXV or an orifice tube?

What is the compressor RPM at flying speeds?

The 110 psi static is probably just the refrigerant picking up engine bay heat. You have a condensing problem. The OEM condenser is a Serpentine. A good design, but difficult to flush properly, and nearly impossible to tell is one or more channels are blocked. Try using a garden hose on the condense...

Sometimes with replacement condensers of a type different than the OEM, the charge level changes. An overcharged system will have high pressures. For instance. GM changed the condenser in some trucks, and the new part holds 6 ounces less... Sounds like you are doing everything right. 400 psi is a bi...

Well if it is R12 & still has the tube & fin condenser then the charge level should be ok. Does your compressor have 3 way service valves? If so the issue could be the high side valve is not back seated. I never open a service valve more than 1/4 turn from back seated - you only need enough ...

This "newer condenser" - is it an OEM replacement, or an upgrade to a serpentine or parallel flow?

I am guessing this is a 134a conversion. Does it still have a York compressor?

You can gut that QD fitting if you like, but I have never seen one cause trouble. Is your TXV original?

I think that before I tinkered with the control valve assembly, I would find the cause of the high pressure. The low side seems to indicate the compressor is working. Ever try to light 200f alcohol vapor? All it takes is a bad plug wire. I know IPA is not Methanol, but I have worked around enough al...

The valves on the manifold need to be CLOSED to evaluate a system.

Run the system with the gauges attached, valves closed. Run it at idle, then at 2000 engine rpm. Record the pressures at both speeds, as well as the vent temperatures and ambient temperature. Post the results.

1984 was the last year for the A6 in that truck. 1985 was either an R4 or an HR6 / DA6 depending on where & when it was built. The OEM hose set is probably hard to find given the age. A used set can be rebuilt with fresh rubber at most commercial hose shops. The A6 was never happy as a CCOT comp...