According to my reference sources, your van with an OEM front and rear A/C system calls for 46 ounces of R-134a. With an aftermarket rear system added to the front OEM unit, the exact amount of refrigerant becomes a guesstimate. Did the shop happen to tell you how much they put in it?

Considering the operating conditions and the R-12 to R-134a conversion factor, the pressures look pretty good to me. The vent temps, no so much. At a fast idle, 25 psi on the low side gives an evaporator temp of around 30 degrees, which should result in plenty of cool air in the cabin. As Tim sugges...

Thanks for the explanation, which clears up everything. As you guessed, that side-mounted condenser loses most of its efficiency (and the ability of the system to cool) due to the lack of natural airflow passing through it while driving at speed. So it must rely on the fans virtually all the time. N...

Are you sure the system takes 46 ounces of refrigerant? My reference material for your vehicle says 32 ounces of R-134a and 8 ounces of PAG-100.

I agree that the rental manifold gauge set connectors probably aren't depressing the vehicle's shrader valves. Assuming for a moment that the connectors themselves aren't defective, they can fake you out in that rotating the knobs CLOCKWISE (not counter-clockwise) actually depresses the shraders for...

The reason I originally suggested that your vent temps and pressures are wacky is because they are, at least to me. With the rear A/C off, you have vent temps of 36-38 degrees, which are pretty cold. With the rear A/C on, the temps range from 47-54 degrees, which are on the warm-ish side. Such a wid...

Your varying pressures and vent temps are certainly wacky. Are you sure that the charge is still correct and that you don't have another leak someplace? I suggest recovering the charge to verify that first.

I'm wondering about a few things. Since you mentioned an aftermarket "side-mounted" condenser, is the entire system aftermarket? If not and the rest is OEM, does it have front-and-rear A/C or front-only? The reason I ask is because there's a substantial difference in the amount of refriger...

DEFINITELY DON'T ADD ANY SEALER TO THE SYSTEM. Doing so will only create more very costly problems. Find the leak, repair it, evacuate and recharge the system, and you'll soon be driving in cool comfort again.

I agree with everything that Tim and Cusser said, especially about the leak. If you live in the Northeast where most towns and cities use tons of salt on the roads to melt snow and ice, you might have a pinhole leak in a hard line due to corrosion, which in turn would cause a slow loss of refrigeran...