Found system shut off on compressor overheating lockout code. Took off locking calls to check refrigerant standing pressure. Noticed oil around liquid line service valve. When the call was removed the Schrader core was leaking. Adjusted Schrader core until leaking stopped. Performed leak search through while system with no findings, other than by the leaking service valve. 2nd tech checkout- leak repaired still low charge, ran in pumpdown mode to prevent low lockout while changing, changed to heat check charge. system very low,allowed unit to equalize to correct pressures Mr. Keeps house very warm, 78 in door temp. Is ordered New sensor can recheck system when installing part