I have a small can of R-12 and hook-up hose. Where do I attach the hose on my '89 F-150 w/ 5.8L V8? I had an A/C guy stop by my house and look at the truck. He thought it just needed a re-charge. I think I remember him saying the low-pressure service port where I attach the hose from the freon can is on the right side of the engine (high-pressure being on the left) Correct? Also, the plastic cap on the port on the right has split and fallen off. Is it important to have a cap there to prevent leakage? Or is it just to keep out debris? Where can I find a replacement? It's bigger than a tire valve stem cap. Can I just wrap black electrical tape around it for now?

thanks
Jim