Air Conditioning System Components Compressors Compressor Clutches Condensers Expansion Devices Evaporators Receiver-Driers/Accumulators Switches and Evap. Temperature Controls Rear AC Systems

CompressorsThere is a large variety of compressors. Some of variations are:

The compressor manufacturer

Piston, vane, or scroll type

The piston and cylinder arrangement

How the compressor is mounted

Style and position of ports

Type and number of drive belts

Compressor displacement

Fixed or variable displacement

Compressor Operation

The compressor increases the refrigerant pressure about five to ten times. This increases the temperature so heat can leave the refrigerant in the condenser.

Out/Discharge: High Pressure, about 200 psi & High Temperature, above ambient

In/Suction: Low Pressure, about 30 psi & Low Temperature, close to freezing

Piston Compressors

Animation: Piston Compressor

Shaft Seal

Reed Valve Plate

Piston

Connecting Rod

Crankshaft

This two-cylinder compressor uses a crankshaft to move the pistons up and down. Refrigerant flow is controlled by the suction and discharge reeds in the valve plate.

Reed Valves

Suction Discharge

Evaporator Pressure Condenser Pressure

Suction Reed Open

Discharge Reed Open

Refrigerant flow can be controlled by reed valves. Pressure on one side of the flexible reed forces it to close the port. Pressure on the opposite side forces the reed open.

Scotch Yoke Compressors

Animation: Scotch Yoke Compressor

A Scotch yoke compressor has two pairs of pistons that are driven by a slider block on the crankshaft. The pistons are connected by a yoke.

Discharge Reed

Pistons with Yokes

Suction Reed

Crankshaft

Slider Block (hidden)

Scroll Compressors

Animation: Scroll Compressor

Orbiting Scroll

Fixed Scroll

Clutch

Shaft SealCrankshaft

The orbiting scroll is driven by the crankshaft and moves in a small circular orbit. The fixed scroll remains stationary.

ScrollsOrbiting Scroll

Fixed Scroll

The fixed scroll is secured to the case so it does not move. The orbiting scroll moves in a circular motion as it is driven be the crankshaft.

Swash Plate Compressors

Swash

Plate

Shaft SealValve Plate

Piston

Valve Plate

Swash Plate Compressors

Animation: Swash Plate Compressor

Pistons

Swash Plate

Shaft SealClutch Assembly

The swash plate is mounted at an angle onto the drive shaft. It drives three double-ended pistons. Two sets of reeds control the refrigerant flow in and out of the cylinders.

Reed Plate

Wobble Plate Compressors

Animation: Wobble Plate Compressor

Wobble Plate Drive Hub

Piston Connecting Rod Shaft Seal

Valve Plate

Variable DisplacementLow Angle Minimum Stroke

High Angle Maximum Stroke

Control Valve

The evaporator pressure has dropped, and the control valve has increased crankcase pressure

Normal operation when cooling is required. Crankcase pressure is low.

Variable Displacement Wobble Plate Compressors

Control Valve Valve Plate

Piston

Connecting Rod

Shaft Seal

Pivot

Vane Compressors

Animation: Vane Compressor

Rotor Vane

Shaft SealDischarg

e Reed

The rotor is driven by the clutch and driveshaft. The vanes move in and out of the rotor to follow the outer wall to pump refrigerant.

Vane Compressor, Cutaway

Shaft Seal

Discharge Check

ValveRotor

Vane

Clutch:

Pulley Plate

Coil

Clutch Assembly

Drive PlateCoil

Pulley

The three major parts of a clutch assembly.

Compressor ClutchMost compressors use a three-part clutch: the hub, rotor, and coil.

The hub is attached to the compressor drive shaft. It has a plate that is pulled against the rotor when the clutch is applied.

The rotor is driven by the accessory drive belt; it is mounted over the front of the compressor using a bearing so it can rotate.

The coil becomes an electromagnet when current is sent through it.

V-belt Pulley

Multi-Vee Pulley

Hub Pulley/ Magnetic Rotor Coil

Clutch Operation

Animation: Clutch Control

Current is sent to the clutch coil to energize the magnet and apply the clutch. Shutting off the current flow releases the clutch and stops compressor operation.

Pulley

Coil

Clutch Hub/Plate

Condenser TypesCondensers A and C are round tube, serpentine condensers.

Condenser B is an oval/flat tube, serpentine condenser.

Condenser D is an oval/flat tube, parallel flow condenser.

Flat tube condensers are more efficient.

Serpentine Condenser

Refrigerant flows from the upper inlet to the bottom outlet through two tubes. These tubes wind back and forth though the condenser.

Parallel Flow Condenser

Refrigerant flows from the upper inlet to the bottom outlet through groups of parallel tubes. Some carry refrigerant from the right to the left, and others move it back to the right side.

Expansion Devices The expansion device separates the high side

from the low side and provides a restriction for the compressor to pump against.

There are two styles of expansion devices: The TXV can open or close to change flow. It

is controlled by the superheat spring, thermal bulb that senses evaporator outlet temperature, and evaporator pressure

Most OTs have a fixed diameter orifice

Thermal Expansion Valves, TXVsThe three major types of expansion valves:

Internally balanced TXVs are the most common.

Externally balanced TXVs are used on some larger evaporators.

Block valves route the refrigerant leaving the evaporator past the thermal sensing diaphragm so a thermal bulb is not needed.

Animation: TXV Operation

Internally Balanced

Externally Balanced

Block Valve

Orifice Tubes, OTs

The OT used in a modern vehicle is a tubular, plastic device with a small metal tube inside. The color of the OT is used to determine the diameter of the tube. A plastic filter screen is used to trap debris that might plug the tube.

Some older General Motors vehicles used an OT that resembled a brass fuel filter.

Orifice Tubes, OTs

Evaporator Types

Plate evaporators, top, are a series of stamped aluminum plates that are joined together. Tube and fin evaporators, bottom, have tubes for the refrigerant that are joined to the fins.

Receiver DryersA receiver dryer is mounted in the liquid line of a TXV system. It is used to:

•to store a reserve of refrigerant.

•hold the desiccant bag that removes water from the refrigerant.

•filter the refrigerant and remove debris particles.

•provide a sight glass so refrigerant flow can be observed.

•provide a location for switch mounting.

Barb Connections, Note Sight Glass

Male Flare Connections

Male O-ring Connections, Note Switch

AccumulatorsAccumulators are used in the suction line of all OT systems.

The accumulator:

•separates liquid refrigerant so only gas flows to the compressor.

•Allows oil in the bottom of the accumulator to return to the compressor.

•provides storage for a refrigerant reserve.

•contains the desiccant bag for water removal.

•provides a place to mount low pressure switches and sensors.

Receiver Dryers/Accumulators

Switches Ambient temperature High pressure Low pressure Compressor rpm Compressor superheat Compressor high temperature Compressor cutoff

Switches ECT Evaporator pressure Evaporator temperature Pressure cycling Thermostatic cycling Trinary pressure

Switches

Switches

Switches

Evaporator Temperature or Pressure Controls EPRV EPR ETR POA STV VIR