This is not a job to be done by a backyard mechanic. The pressures are irrelevant as you will have to take this to a shop to be done anyway.
Not sure why anyone would say you need to take it to a shop just for a recharge. Since around 1995 when manufacturers started using R-134 "freon" instead of the old R-12, charging a system has gotten a lot easier. The fittings are different for the low side (suction) and the high side (pressure), so you can't connect to the wrong port.
You can get cans of R-134 from Wal-Mart for under $9.00 (12 oz.), and even get the lows side hose kit (usually blue in color to indicate low/suction/cold. But for about $17.00 at Autozone, they have a low side kit that has the "puncture" fitting to connect to the can, a hose that connects to the suction port on the car, and a built-in suction gauge marked for the desired suction pressure.
Basically, open up the puncture valve so it is back from where the can connects, connect it to the can, connect the other end to the car's suction port (only fits the correct port), then start the car. Run the A/C full on, windows down, max cool. Now, close the puncture valve so it pierces the top of the can, then as you open it up, R-134 will be sucked into the A/C system. You can probably point the can downward while it is filling, and you can always feel the hose-end of the can getting colder as freon enters the system.
Once the can feels real light, and the end doesn't feel cool anymore, you're probably done, Usually, if you had been feeling a small amount of cooling before, one can will be enough to fox things. Close the valve, tun the engine off, then disconnect the hose from the car. Replace the protective cap that was on thew valve in the first place - this protects the valve from dirt, but more importantly, it makes sure the freon doesn't leak out the service port. There should be a cap on the pressure point as well. If either cap is missing, get a replacement from an automotive parts store.
Don't let anyone tell you that you "have" to take it to a shop. As long as the "parts" are working OK, a recharge is pretty easy.
...................... Above is correct, and do not get discouraged if everything does not work perfectly (cold air) at first. Mine took a couple of days to re-lubricate the compressor and function correctly. The cost was $21.oo, and patience, instead of 350.oo at a shop.
[bjranson] Agreed. I just did it with a R134 can/pressure gauge kit from Walmart - $24. Very straightforward, and this is the first time I've ever done such a thing. The guy who said take it to a mechanic is probably a mechanic himself and doesn't want to lose business and hundreds of $ to DIYers. Either that or he's just scaremongering.
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