I just put a new battery in my 99. Sometimes when I turn the A/C on it doesn't come on. Sometimes it works just fine. I am guessing that a relay is dying. Has anyone else had this problem? Does anyone know where the A/C relay is?

 

Underhood Junction Box. Just swap the relay with one that is identical.

I suspect it is low on refrigerant. You can jumper out the low pressure switch to rule that out (either short BK/YE to ground, or jumper BK/YE to RD/YE at the pressure switch connector, on the filter dryer). If it works reliably when jumpered, you need servicing. Personally, I'd have a paper clip handy, wait for it to fail, pull that connector off and jumper it. If it comes on, it either needs serviced or needs a new pressure switch (it's called a cycling switch) and it is replaceable without de-servicing. It's also pretty cheap and readily available (NAPA).

Could also be a worn compressor clutch. As the gap increases, it won't reliably engage. They can be shimmed.

 

I will check those things out. It seems like the compressor isn't kicking on sometimes when I turn the A/C on. I hope that it is just the relay going bad.