A/C problem, suspect TXV - Please help

[jonb]

I have an A/C unit on the site I work on that keeps tripping on LP. Initially thought it could be a refrigerant leak so evacuated the refrigerant which weighed in at the correct system charge. I carried out a pressure drop test which was OK and then vacuumed down the system. I recharged by weighing in the refrigerant to the correct system charge.
When I run the unit the suction pressure drops very quickly and the unit trips on LP. The LP pressure then doesn't raise again for several hours.
I have checked the temperatures either side of the filter/drier and that seems OK. I am thinking its a faulty TXV but as I work on a gas site and getting an open flame permit is quite difficult I am hoping someone has another diagnosis. I tested the TXV with hot water but still no inrease in pressure until I adjusted the screw to fully out and then a got a small rush of refrigerant and a small increase in pressure. All coils are clean. Please help

[The Viking]

What unit are you looking at?

Manufacturer?
Model?

.

[jonb]

some crappy Korean thing called Kingstec PA-756AY.

Theres no data on the internet about these things and have no documentation.

I work in Northern Russia so a lot of the equipment is not standard.

[jonb]

Its also R22

[robertniez1961]

Got a job similar to the problem you encountered i just replace the txv and it was again working. As i inspect the txv that i've remove the straine is plugged.

[Mick13]

sounds to me like the txv bulb has lost its charge, inspect the bulb and capillary leading from the bulb to the valve for breaks/wear.

it just occurred to me actually that on some valves the top section can be replaced without needing to replace the body, eliminating the need for brazing, if this is the case and the bulb has lost charge.

[jonb]

Thanks for the replies guys. I think I will just replace the TXV and the filter/drier at the same time. If I go through all the trouble of getting a hot works permit I may as well do the lot. Thanks again