The pressure switch of the Jahn-Teller deformation direction in (ND 4 ) 2 Cu(SO 4 ) 2 .6D 2 O was investigated in the temperature range 130-320 K. Below 295 K, the new, pressure-induced phase, is stable under ambient pressure. Switching back is observed on heating to above 297 K. In the range 150-295 K a strong temperature dependence of the switching pressure (from 24 to 450 MPa) is observed. Below 150 K, the switching process is slow and a coexistence of two phases is observed. We conclude that the switch of the Cu(D 2 O) 6 complex deformation direction is the Jahn-Teller response to the changes in the hydrogen bond system.