Air Conditioning CircuitAir Conditioning Circuit

Columbia Basin College

Automotive Technology

The Basic Cycle 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 Transfer of Heat Relies on Pressure ChangePressure 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 Pressure’s Effect on Gases and Vaporsand 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 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 Temperature - Pressure RelationshipRelationship

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 SystemBasic A/C System

Two copper coils– one coil is evaporator– one coil is condenser

Between coils is a compressor Fans

page 68C

CompressorCompressor

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 VALVESSERVICE VALVES

A/C Service ConnectorsA/C Service Connectors

CondenserCondenser

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 Expansion Valve or Fixed Orifice TubeFixed 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.

EvaporatorEvaporator

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

FansFans

One fan to circulate air through evaporator fins

One fan to circulate air through condenser fins

High Pressure SideHigh 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 SideLow Pressure Side

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