In an evaporator having plate-type construction, a plurality of stack plates are stacked atop one another such that a first fluid passage for a first fluid as a refrigerant and a second fluid passage for a second fluid as a coolant is provided and are formed between the stack plates. The stack plates have first apertures for supply and return of the first fluid, second apertures for supply and return of the second fluid, a first inlet opening and outlet opening for entry and exit of the first fluid, a second inlet opening and outlet opening for entry and exit of the second fluid, and an expansion valve for the first fluid that is built onto or integrated into the rest of the heat exchanger. The evaporator incorporates a shutoff unit for the first fluid that is built onto or integrated into the rest of the heat exchanger.