Air Conditioning Circuit Columbia Basin College Automotive Technology

The Basic Cycle Heat is picked up by the Evaporator Fins Heat picked up by the liquid refrigerant as it evaporates. Heat-laden refrigerant vapor is pumped by compressor into the condenser The refrigerant in the condenser is given up to the less-hot air passing across the condenser coils as it condenses back to a liquid

Transfer of Heat Relies on Pressure Change Low Pressure of 21-35 lbs - Temp of 21-28 degrees F High Pressure of 180-220 lbs - Temp of 88-100 degrees F Anytime there is a pressure change there is a temperature change Anytime pressure & temp changes there is a change of state

Pressure’s Effect on Gases and Vapors Pressure affects the temperature of gases and vapors by raising it’s boiling point. Compressing a gas or vapor increases its temperature because the same amount of heat is concentrated into a smaller space. The temperature of the gas or vapor can be raised without adding extra heat.

Refrigerant Changes State Low Pressure side - Liquid to a Vapor Low side tubing is often cool enough to collect frost or water droplets on high humidity days. High Pressure side - Vapor to a Liquid Tubing diameter is often smaller than on the low side Hotter than the low side tubing

Temperature - Pressure Relationship Heating refrigerant causes it to expand. Different refrigerants have different expansion rates. When confined in a enclosed place, a increase temperature is always accompanied by an increase in pressure. For a given temperature, a corresponding pressure will exist in a container of R-12 or R134a

Basic A/C System Two copper coils Between coils is a compressor Fans one coil is evaporator one coil is condenser Between coils is a compressor Fans page 68C

Compressor Pulls in low-pressure vapor Pumps out high-pressure vapor Provides a endless cycle of cooling Condenses, Evaporating and heating Raises pressure and temperature of refrigerant entering condenser to a point where it can transfer heat to outside air through the condenser

SERVICE VALVES

A/C Service Connectors

Condenser Located in front of radiator Compressor pumps high pressure vapor into condenser where ram air passing over coils carries off heat The heat loss causes the refrigerant to become a high-pressure liquid.

Expansion Valve or Fixed Orifice Tube Provides a restriction in refrigerant flow which the compressor can build up a pressure in the condenser. Compressor suction lowers pressure in the evaporator Regulates pressure differential between the high and low sides. Keeps evaporation and expansion of refrigerant and most efficient level.

Evaporator Function is opposite of condenser Evaporator coils remove heat and humidity from the air being circulated in passenger compartment. When liquid refrigerant absorbs heat, it again becomes a vapor under low pressure Has a tray to collect moisture from fins

Fans One fan to circulate air through evaporator fins One fan to circulate air through condenser fins

High Pressure Side High side includes Discharge side of Compressor High Pressure vapor lines to condenser Condenser High Pressure liquid lines to orifice valve Inlet side of orifice Valve

Low Pressure Side Includes: Orifice Low Pressure Liquid lines Evaporator Low Pressure Vapor Lines Suction side of Compressor Outlet side of orifice valve