Bob and Tim are looking at a system that has a frozen evaporator coil. The system is in a home. They are talking about what has happened to the system and what to do about it.

The first point to understand about refrigeration theory is that heat is energy, and it can be made to move. If enough heat is removed from a glass of water, the water will freeze to ice. When that heat is allowed to move back into the ice, the ice will melt.

An iced-up evaporator is a common service call for any service technician working in this industry. Generally, determining this is the cause of the system problem is rather easy. But what caused the evaporator to ice up may not always be obvious.

Compressor performance curves can provide a service technician with the Btu pumping rate (capacity), mass flow rates, operating amperage, and operating wattage of a compressor when the suction pressure and head pressure are known for the system.