So I just bought a 98 Xj limited a few days ago and the a/c only blows out hot air. I bought some r134a because I thought that might be the problem. However, when I hooked up the gauge to the right port, it was reading about 120 psi. The compressor engages fine. Any ideas what it could be?

 

Are you getting 120 PSI on the low pressure port? That's way too high...normally runs about 40 PSI.

 

hot air, high pressure.... could be the high low switch?