How to Use the Color Key Colors are used throughout Auto Heating and Air Conditioning to help show different refrigerant states. Other colors are used to illustrate nonrefrigerant liquids and gases, as well as electrical, mechanical, and special components. The follow- ing key shows what each color represents. Refrigerant States High-pressure liquid Low-pressure liquid High-pressure gas/vapor Low-pressure gas/vapor Components Evaporator, heater core, condenser, radiator Compressor Accumulator/receiver-drier Metering devices, orifi ce tubes, thermostats, expansion valves Electrical Electrical-computer Supplemental restraint system (SRS)/air bag Airfl ow Hot air Outside air Cold air Recirculated air Blended air Nonrefrigerant Liquids and Gases Engine coolant Nonrefrigerant gas, engine vacuum Refrigerant oil Other Special features or components not otherwise coded. 4 Auto Heating and Air Conditioning