Solenoid valves are used to control refrigerant flow within the climatic chamber. The frequent switching of the solenoid valves is not ideal for electromechanical relays. Additionally, refrigerants might also be flammable (A2L, A3 categories) which would require switching devices to be non-arcing. Solid state relay such as RP1A and RP1D can be easily mounted directly to a PCB board and also to a standard DIN rail (via the additional accessory). The inherent solid state design does not produce any arcing and, on top of that, there is no contact lifetime issue.