1. Air Conditioning Circuit
Columbia Basin College
Automotive Technology

2. 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

3. Transfer of Heat Relies on Pressure Change
Low Pressure of lbs - Temp of degrees F
High Pressure of lbs - Temp of degrees F
Anytime there is a pressure change there is a temperature change
Anytime pressure & temp changes there is a change of state

4. 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.

5. 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

6. 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

7. 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

8. 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

9. SERVICE VALVES

10. A/C Service Connectors

11. 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.

12. 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.

13. 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

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

15. 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

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