I quickly looked through some of the Vintage air site, didn't see a reference to what type of metering device is used. A TXV or electronic expansion valve (EEV) would certainly be the preferred method over a fixed orifice. If their kits are using TXV's, good on them. One thing I noticed in a troubleshooting guide was the mention of charge weight of 1.8 lbs., I don't know if every application could use the same amount of refrigerant but if the kit spec'd a certain charge then I would go with it. Non-condensables (oxygen, moisture, nitrogen, oils, etc.) will give some of the symptoms that have been described in this thread. A good place to start would be a complete recovery of the existing refrigerant, deep evacuation, weigh in a new charge per spec.
