Recently we had a troubleshooting session on our Split type Air conditioner and the mechanic refilled the refrigerant gas to 70 psi pressure. He had been working in a medical college cum hospital and having specialized in AC and refrigeration, he said that mortuaries are being refrigerated to 4*C and they require a R-22 pressure of around 20 psi. And I am struck with this: If at home, the cooling is insufficient, we increase the pressure to around 70 psi. But why is it that we have to maintain the pressure of refrigerant at around 20 psi for centralized AC in mortuaries? In the former case, gas pressure is directly proportional to cooling effect apparently and it is converse in the latter case. How is it evident?