I would suggest finding an honest A/C service person. Technically, you need an EPA license to handle R-22. You might have a pinhole leak in your system, which requires evacuation of the system and a pressure test to locate. For this, you need a vacuum pump, guage set, evacuation cannister, replacement R-22, a filling device that will let you add the exact amount of refrigerant required for the unit, a couple of new Shrader valves, a torch and brazing solder and some replacement copper. It is rather involved. I don't do this type of service even though I have the EPA Universal air conditioning and refrigeration license due to the very high equipment costs, the outrageous processing fees for R-22 and the high liability factors involved. OTOH, if your system is just needing a little R-22 to top it off, then it should not be a problem with the proper equipment!
This is why the RV industry went away from the Armstrong type units and went with the new hermetically sealed units that are cheaper to replace than repair.
Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
SOLAR TECH ENERGY SYSTEMS, INC.
AM SOLAR ...MAGNUM…VICTRON ENERGY...LITHIUM & LIFELINE BATTERIES…MARINE REFRIGERATION