My 1995 XJS has been idle for 6 months and now my AC is blowing warm air ... help!
I generally can resolve most issues but have not experience with the AC. Would appreciate some help, thank you!

 

Is the compressor turning on? What are the suction and discharge pressures? You will need a R134 manifold gauge set for that and to properly charge the system. Amazon and Harbor Freight sell them at reasonable prices. In my experience a low charge is the most common problem. You need to know the system pressures to charge it properly.

 

Yes, the Harbor Freight manifold works great. Make sure you buy cans of r134a WITHOUT any kind of conditioners or sealants. You don't want to introduce anything like that into the system.

 

Yes, most likely you are just low on coolant, R134.
Not running the AC in the winter is usually the culprit for older cars with no AC in the spring. The "O" rings don't get lubricated and they shrink allowing coolant to seep out.
Check your manual for the proper pressure but most are in the 2.5 lb range. Fully empty that is three 12 oz cans.
Auto Zone has a free loaner program that you can get an entire AC kit from minus the coolant.
Finally, once you have the system back to running normally yo might want to give it a shot of coolant dye (usually flouresant green or orange) that will indicate where you have a leak if it continues. An alternative might be to assume you have "O" ring leakage and go ahead and replace them before adding new coolant and dye to the system.

 

Seán, I did as Brad suggested above in my ’95 XJR last week (similar engine etc to yours), and added some 134a using a simple kit such as this
https://www.walmart.com/ip/Honeywell...ssType=REGULAR

though I only needed to add one can. It only takes a few minutes to do—give the can a good shake then attach to the low pressure AC hose (it is the larger of the two) and squirt, stopping to check the gauge every so often. The included instructions make it easy.