Got a cvhe that had high pump out mins. and a nasty surge starting as soon as it started to load. Contractor recommended pulling charge, which showed machine to have lost 300 pounds of 1000 pound charge. Vacuum was pulled down to 430 microns, and rose less than 200 microns over the next 17 hours. That says tight machine to me. Virgin charge was weighed in, and machine purrring like a kitten now at full load; however, purge stated cycling immediatley as if air were present. temp sensor on purge was verified accurate - pumpout happening as it should. Superheat is dropping just like it would if non condensibles were present. Charge on purge was checked by subcooling per IOM - ok. Gas inlet from condenser was valved off; purged continued to cycle as before. Contractors theory is that purge is leaking the 134 a into the purge tank, which is reducing the evaporating surface and lowering the superheat. Not sure if I agree with that, but I cant think of another scenario which would explain what we are seeing. Any of you guys seen this before?
Cant find spell ck - sorry