99 Silverado A/C trouble

I've never had my air conditioner serviced or fixed in all the years I've owned this truck! Finally a/c seems to be giving out. Will blow cold immediately after being switched on, but after an hour or so the
cold air stops and so does the pressure of the air. If I shut off A/C switch, air pressure gradually increases again.
Almost like something's freezing down there.
What can cause this?
thanks. c
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It is in fact freezing the core. I have one that does that sometimes. You likely have a low pressure cutout switch that is out of spec. The switch coutout is adjustable when you remove plug to it with a small screw driver. Turning screw clockwise lowers cutout pressure (makes it colder) and counter clockwise raises it. Try about one full turn which is about a 3 PSI change. ALso try to maintain higher blower speeds (3 and above) at all times as low speeds makes it more prone to freeze. Your problem is not that rare. ----------------- TheSnoMan.com
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