Air Conditioning Components

Agenda AC Components Compressor & Clutch Condenser Receiver-drier or Accumulator Expansion Valve or Orifice Tube Evaporator

Compressor 2 primary purposes Increase pressure & temperature Circulate refrigerant Engine driven pump via belt Compressor capacity to move refrigerant is primary determinant of the heatremoving capability of the system

Compressor Therefore larger compressor = larger BTU capacity of system 3 basic types Piston Rotary vane Scroll type

Piston compressor Pistons may be arranged inline, V, axially or radially Intake stroke Compression stroke

Piston compressor

Rotary compressor Usually cylindrical in shape Reduced noise & vibration (balance) More cylinders = balance

Rotary compressor

Variable compressor Same as swash plate rotary compressor Pressure sensed by the low or suction side of the system changes the swash plate angle Changes cubic inch displacement

Variable compressor

Compressor Clutch Belt driven compressor without variable displacement needs to have compressor shut off Clutch controlled electrically (electromagnetic clutch) By AC control panel or by system demands Most OT system require compressor on/off to control evaporator temp

Compressor Clutch Components: Drive plate attached to compressor shaft Drive pulley mounted on bearings that are attached to the compressor housing Magnetic coil mounted in behind pulley, does not rotate

Compressor Clutch

Clutch problems Slippage load Slippage voltage Clutch heat electrical resistance Air gap Electrical shorts

Condenser Function: To remove heat from refrigerant Receives hot compressed refrigerant gas from compressor Outside air flows over fins of condenser and heat is transferred to the air Temperature lowered below boiling point

Condenser Construction: Coiled tubing in a series of fins (surface area) Refrigerant moves from top to bottom (heat rises) Older systems one tube bent into multiple S shapes Newer systems side manifolds for multiple paths for flow

Condenser Installation: directly in front of radiator for full airflow

Condenser

Receiver/drier(Accumulator) Function: Serve as a storage tank for refrigerant Absorb any moisture in AC system RD receives liquid refrigerant from condenser and holds until needed by evaporator Capacity varies according to operating conditions ½ pound extra

Receiver/drier(Accumulator) Location: Usually used in TXV systems Mounted in liquid line between condenser and expansion valve

Receiver/drier(Accumulator)

Receiver/drier(Accumulator) Sight glass indicator for amount of moisture Undercharge bubbles Cloudy moisture Oil streaks Clear

Receiver/drier(Accumulator)

Accumulator Used in CCOT systems Restriction placed in inlet to evaporator and is fixed in size High engine speeds and low heat load, evaporator floods with liquid Liquid and compressors do not mix Accumulators will collect liquid and store until

Accumulator

Evaporator Similar to condenser in construction Receives refrigerant from metering device as low pressure liquid Liquid receives enough passenger compartment heat, refrigerant changes state to vapour Evaporator flooding too much liquid refrigerant enters = poor cooling

Evaporator Outlet temperature 4-16F higher than liquid inlet Blower speed vs temperature absorption & volume

Evaporator

Metering devices Orifice Tube TXV Designed to provide a restriction to cause a pressure (high side) and then cause a pressure drop (low side) and therefore temperature drop Meter refrigerant into evaporator

Orifice tubes Plastic tubes installed in the liquid line between the condenser outlet and the evaporator inlet Screens to remove contaminants Calibrated metal orifice tube to meter refrigerant flow

Orifice tubes

CCOT system operation Compressor is turned on and off to control refrigerant flow and pressure Pressure switch, mounted after evaporator monitors outlet pressure (temperature) As pressure increases (liquid refrigerant absorbs heat and temperature increases) compressor will turn on and allow more liquid refrigerant

CCOT system operation When pressure drops too low, (too low temperature) the pressure switch reacts and turns off the compressor (flooded evap)

TXV Thermal expansion valves have modulating action Fluctuate open/closed in order to keep evaporator output temperatures stable

TXV - construction A sensing bulb with a temperature reactive gas is in contact with the evaporator outlet tube Spring pressure on the bottom of the valve will try to keep it closed The pressure in the sensing bulb acts upon the diaphragm and forces the valve open against spring pressure

TXV - construction

TXV - construction Internally vs externally balanced Internal balance tubes connect pressure from evaporator inlet to bottom side of TXV diaphragm This allows for balanced pressures and smoother, less abrupt metering

TXV - construction

H-valve - construction Two passages evaporator inlet and outlet with a pressure sensitive diaphragm in an H shaped housing Temperature sensitive element on the evaporator outlet controls the orifice size on the evaporator inlet

H-valve - construction