The coolant circuit (15) contains a conventional compressor (11), condenser (12), expansion valve (13) and evaporator (14). Between the condenser and expansion valve a two-port two-position magnetic stop valve (30) with spring bias is introduced and operated by electronic control (31) in response to signals from a gas sensor (33) in the air distribution duct (16) downstream from the evaporator. The control also operates on servomotors (26, 28) opening and closing the flaps (18, 27) and gives visual and audible warnings (32) of any leakage of coolant from the evaporator into the air flow leaving the circulation fan (17).
