New installed complete 5 ton system with TXV. The discharge thermostat is shutting condenser off after about 2.5 - 3 hours of run time. Then after about 2 hours the condenser runs again (discharge thermostat resets itself).

I checked customers subcooling, it is 18. I am thinking system is over charged. System is a 12 Seer Armstrong.

If I have this right I need to lower subcooling to around 12-15 by letting out some freon. I do not know what the subcooling should be for sure on an Armstrong unit. Can someone inform me what it is for an Armstrong 12 Seer?

The 18 subcooling is making the compressor run harder and causing higher discharge pressure which causes higher discharge temperature. Thus causing the discharge thermostat to over heat and shuts the condensor off.

Do I have this right?