Find a repair tech that knows what they're doing. That's the best advice I can give with the limited information given.
No reason given for why the "metering valve" was changed or what kind of device it was.
Lots of reasons the low side will pull into a vacuum. One reason it will is that the condenser's compressor is doing it's job. Why it is should be an easy thing for any AC tech with experience to figure out.
Sounds like a parts changer to me IMO with the information provided.
Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.