Is the compressor cutting on when you turn the a/c on?
How many miles are on your KJ?
Ideally if you want to get the most accurate reading of the performance of your a/c, you need to have one of the guage sets that professional mechanics have...and they're expensive.
However, I have a guage i bought at wally world that came with a can of r-134a which is what all modern vehicles use. It only checks the low pressure side of the a/c system, which is what goes too low when you're low on freon (if that makes any sense). It's also got a spot for the can to plug into the back of it, with a trigger on it so I can control how much freon I want to add, plus it shows me the level while i'm adding.
To check your a/c, firs everything must be functioning properly...and by that I mean your a/c compressor needs to be running. If it is, set the a/c on max (or recirculate) and turn the fan speed to 4. Hook up your guage to the low pressure side of the a/c system. There are 2 different ports that look exactly the same. One is the high pressure, the other is the low pressure. The guages you can get at any autoparts store only fit onto the low pressure side, so you can't go too wrong with this. Next look at the guage and see what it's reading. Too little freon and it will blow warm, too much will also cause it to blow warm. If you need some, hook your can up to the back of the guage unit and add untill full. Be sure to follow the directions on the back of the can (usually cal for holding the can upside down while you're filling it).
The low pressure port is located to the left of the engine if you're facing it. It's towards the back.
This isn't the greatest picture, but here's where the low pressure port is located on the 3.7. Just unscrew the little black cap and youre good to go with checking it.
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