Yes, low charge will cause short cycling. What that means is the compressor is cycling out too soon and doesn't run long enough to work properly. There is a pressure switch on the low pressure side of the system that will cut power to the compressor coil at a certain setpoint, usually around 20PSI. There are 2 reasons for this-one is to protect the compressor from running when there is not enough refrigerant/oil being pulled into it, the other is to keep the evaporator from freezing up. If there has been nothing done to the system in 20 years, it's very likely low. No a/c system keeps its charge forever. Eventually, seals and o-rings get old and start to leak. If it's a small leak, you may be able to get a shop to top it off, or go to a parts store and get a can of 134a and a low side hookup. This would allow you to top it off yourself. Hope this helps. Scott |