My Saleen is also 13 years old. I start it every week, all year long, but it gets driven only about 1000 miles a year. I make sure to run the A/C every time I start it... Keeps the compressor oil and refrigerant moving through the system. My A/C has been flawless... Coldest of all my vehicles, by far.
You may have lost your refrigerant charge... Which means you have a leak... Probably due to O-rings drying out. A re-charge might help / restore it, but it could be temporary if the O-rings are really dried out. The problem is then finding the ones that are dried...
The easiest thing to do is replace all the O-rings during the recharge. Go ahead and replace the orifice tube too... Cheap insurance. Total parts cost is about $30.
Have a shop discharge the system for you... Then take it home and swap out all the seals yourself. Then take it back to the same shop and have them re-charge the system for you... Should be about $100 to $150 for labor and refrigerant.
You can buy the O-ring kit for cheap:
https://www.carparts.com/a-c-o-ring-...#91;year]=2007
Orifice tube is cheap too:
https://www.tascaparts.com/oem-parts...QtNmwtdjgtZ2Fz
This "Nylog" stuff makes asseembly and O-ring sealing a breeze:
https://www.supplyhouse.com/Refriger...QaAtnzEALw_wcB
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