Heater Troubleshooting

[landy]

I've got a '72 with 350 and factory A/C. The A/C system is uncharged, but the compressor does come on. I've verified that all the vacuum operated valves open and close, and all the damper doors close per the manual instructions.

There's hot air always blowing out the ducts (with the fan on). I'd like to be able to get outside fresh air at ambient temperature blowing into the cab. The lever on top of the core box in the engine compartment moves with the control lever, so that would seem to indicate that the door inside the box is moving.

I think the manual indicates that the vacuum controlled hot water shut off valve should close with the A/C on, which would mean that hot water is always circulating through the heater core. I have vacuum to this valve, but I don't think it's closing. It seems that in order to get outside, uncooled air, it would be better to have this valve at closed or mostly closed except when heat is needed. Am I understanding how this valve is supposed to work correctly? On other older vehicles, there was a valve on the heater line that one could turn off to stop the flow of heated water through the heater core.

Any thoughts on this problem?

Thanks!