1970's heat pump Heil runs in cooling cycle, compressor intermediately runs for approximently 2 seconds, every 30 to 45 seconds, no cold air, all information wirering schematics serial numbers unreadablle or missing, charging ports and service valves was not visiable from service panells, my disanoticslow freon, run valve shutting compressor on and off, or compressor run capacitor faulty.

It may be going off on a low pressure switch or overload in the compressor . You need to put gages on the unit as well as check the amp draw. There are service ports some where on the unit , Good luck, Mike