Hi all

Need help with heat pump chiller whilst still got hair left. 2 identical machines, 2 circuits each. 1 circuit works perfect, other three all suffer high superheat and low suction pressure in cooling mode, work fine in heating mode - short of gas I hear you say? - no, weighed it in to manufacturers instructions, charge spot on. Duff txv perhaps? - no - new ones fitted to cooling circuit - no difference. Also checked: reversing valve - no leaks between high/low, equalisation line on txv is correctly fitted. Each circuit has 2 compressors running simultaneously, a 4 port reversing valve, 2 txv's, 4 check valves, brazed plate evaporator and air cooled condenser. System will regularly trip out on LP switch, but whilst running we are getting 1.9bar suction, 18bar discharge, 30k superheat and 110c discharge temp (R407c) Water on off is about 21/9.
Each circuit holds 40kg gas so taking ages to re-claim and re-charge every time we change anything (no valves) - driving me nuts so any suggestions gratefully received.