[69 Limelight]

69 GTO, POA valve still in place, R-12, 85 Degrees, window/box fan put in front of condenser, 2000 RPM, low side gauge 30, high side gauge 155, tube below expansion valve going into evaporator cold/frosty, tube out of evaporator before POA valve warm. PROBLEM: no cool air out of vents. (coolant hose right cylinder head to heater core clamped off) Tried adding 12 oz. R-12- no change in vent outlet temperature or high side pressure.

[Schurkey]

Low side seems low, high side seems low. First Guess: Undercharged.

I can't picture the POA on the outlet of the evap. The outlet for the evap should be cold, not warm. The inlet and the outlet should be cold, although the inlet may be colder.

Do the air doors work? "No cool air out of vents" could mean there's poor air flow, or it could mean there's lots of warm air. Which is it?

[Joe's Garage]

I agree with Schurkey that it sounds like it is still undercharged.

What does the sight glass in the top of the receiver drier look like - clear or milky/bubbly? If it's not crystal clear, you probably need more freon.

The chart I linked below shows target optimal pressures at different ambient temperatures.

Prior to this, presuming the system was operating colder, had the system been evacuated, vacuumed down for thirty minutes or so and then recharged with the correct amount of R12?

If the system has been open and you don't get all the regular atmosphere (air) out with a vacuum pump before charging, the pressures will come up before you have a full charge. So it could look 'normal' on the gauges and still not make cold air.

When charging the older stuff, we used to add all but one can of freon and then mist the condensor with a sprayer on a hose and blow in another can of R12. That final can used to make a huge difference in the temp at the vents.

But it's also very messy because it will blow water droplets all over everything.

Good luck!

[Squidward]

Is it possible that the heater/blend door is allowing reheat of your cold air? Frosty going in, warm coming out means heat transfer is taking place.

You could try a pair of vice grips on the heater inlet hose coming out of the back of the PS head. That might eliminate the possibility that the heater core is reheating your cold air.

And yes, my initial assessment also thought it a little undercharged. POA is keeping pressure exactly where it should be.