Need help troubleshooting the A/C on a 87 Cherokee XJ. Has not been working for over a year.
When you select AC it blows warm air.
Jumped the compressor clutch and I can here it engage and see it move.
But so far I have not been able to get the compressor to engage with engine running.

Does anyone know where the AC relays are located and how I can check the compressor?

If the freon is low does it keep the compressor from engaging?

Thank you for your assistance.

 

Yes the compressor clutch will not engage if the refrigerant is low, the low pressure switch won't allow the compressor clutch to engage if the system pressure is too low. You need to get it charged, and a leak dye put in to see if you have leaks.

 

Unless you've already converted it, that's an R12 system. Some shops can still recharge those, but it's not exactly wallet-friendly. last I priced R12 it was over $60/lb.
I'd consider screwing on the R134 conversion fittings, adding a pound of 134 with the PAG oil and running it just long enough to evaluate whether or not the compressor works and no longer. From there you can decide whether or not you want to convert it properly, or whether the project just got too expensive.
As a heads-up, if it leaked away the R12, it'll leak the 134 even worse. Just because the compressor runs doesn't mean there aren't other problems to address... which there are if you have a leak.

 

Take it to an A/C shop if you have no idea of how the system works.