A/C 97 Blazer

97 Blazer 2door 2wd 4.3L 6 Auto 130k miles
I thought it had a problem with the gas charge or something.
One knob has Max A/C, A/C, the A/C to dash and feet, then vent (outide
air to dash, then defrost.
In all but the max a/c position I get good cold air out the appropriate ducts. In max a/c the air flow is slightly reduced compared to a/c, which is not how it used to work. The air coming out is 20 degrees warmer than the a/c position (whch I think cools outside air, whereas max a/c is supposed to recirculate).
Well, at least on a/c I get cold air. In max a/c the compressor does ocome on normally.
Thoughts? Maybe it's time to bite the bullet and get that service manual (from Chevy, I understand the after-market ones ones are not good on accessory non-drivetrain things.???)
Did a quick look on the passenger side for obvious cracked/ brittle vacuum lines and so far did not find any. One poster noted there may be some under the battery - will check there, also.

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