I was revising for my course exam and encountered a question in my book (Applied Thermodynamics for Engineering Technologists, p 66 example 3.3) which stated that a compressor follows a polytropic process to compress air; I understood the calculation process which resulted in heat being transferred to the refrigerant. The problem is that I cannot understand how physically a compressor would be absorbing heat from the environment. I always thought that any type of compression would give off heat. Theoretically I know that for a polytropic process if n=γ the process is adiabatic, if n is smaller than γ heat is given off and if n is bigger than γ heat is received into the working gas (), but I would like to know how this is physically possible. The question I talked about above is the one in the image below. Thanks in advance.