Air Conditioning System Components : Air Conditioning System Components Compressors
Switches and Evap. Temperature Controls
Rear AC Systems Compressors : Compressors There 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
Fixed or variable displacement Compressor Operation : 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 : 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 : 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 : 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 : Scroll Compressors Animation: Scroll Compressor Orbiting Scroll Fixed Scroll Clutch Shaft Seal Crankshaft The orbiting scroll is driven by the crankshaft and moves in a small circular orbit. The fixed scroll remains stationary. Scrolls : Scrolls Orbiting 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 Compressors Swash Plate Shaft Seal Valve Plate Piston
Valve Plate Swash Plate Compressors : Swash Plate Compressors Animation: Swash Plate Compressor Pistons Swash Plate Shaft Seal Clutch 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 : Wobble Plate Compressors Animation: Wobble Plate Compressor Wobble Plate Drive Hub Piston Connecting Rod Shaft Seal Valve Plate Variable Displacement : Variable Displacement Low 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 : Variable Displacement Wobble Plate Compressors Control Valve
Piston Connecting Rod Shaft Seal Pivot Vane Compressors : Vane Compressors Animation: Vane Compressor Rotor Vane Shaft Seal Discharge 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 : Vane Compressor, Cutaway Shaft Seal Discharge Check Valve Rotor
Vane Clutch: Pulley Plate Coil Clutch Assembly : Clutch Assembly Drive Plate Coil Pulley The three major parts of a clutch assembly. Compressor Clutch : Compressor Clutch Most 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 : 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 Types : Condenser Types Condensers 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 : 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 : 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 : 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, TXVs : Thermal Expansion Valves, TXVs The 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 : 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 : Orifice Tubes, OTs Evaporator Types : 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 Dryers : Receiver Dryers A 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 Accumulators : Accumulators Accumulators are used in the suction line of all OT systems.
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 : Receiver Dryers/Accumulators Switches : Switches Ambient temperature
Compressor high temperature
Compressor cutoff Switches : Switches ECT
Trinary pressure Switches : Switches Switches : Switches Switches : Switches Evaporator Temperature or Pressure Controls : Evaporator Temperature or Pressure Controls EPRV