I am having a problem with a txv where the superheat swings between 0-40. The charge looks ok. 300 head 100 suction 10 subcooling. Sight glass clear. This is a new txv old did the same. I took the bulb off suction line valve opens. I tried changing bulb position. I had at 4 oclock as this is a 1 5/8 line. This is on a mcquay 40 ton split. This actually a liquid injection to control superheat. I am just looking for what causes swinging. I can describe unit operation if need be.