WONDERING ABOUT THE CAR AIR CONDITIONING COMPRESSOR?
Most drivers aren’t aware of everything going on under the hood and
behind the dash to keep them cool in the summer and the windshield
clear in the winter. Thanks to the heat-transfer properties of
refrigerant, driven by the car air conditioning compressor, comfort
is just a button-press away.
Air Conditioning Parts
The air conditioning system itself is made up of several main
parts. The refrigerant flows from the air conditioning (AC)
compressor to the condenser, in front of the radiator, where it
releases heat to the atmosphere. Then, heated refrigerant flows to
the expansion valve or fixed-orifice tube. Just past this, in the
evaporator, it absorbs heat from inside the cabin before heading
back to the compressor. Along the way, the refrigerant (usually
R-134a or R-1234yf) goes through tubes and hoses, a filter and a
dryer.
Aside from the switch to engage the air conditioning, the
electrical system uses pressure sensors to determine when to
cycle,engage and disengage the electromagnetic (EM) clutch. On
conventional vehicles, the clutch is driven by V-belts or the
serpentine belt. On hybrid and electric vehicles, the air
conditioning compressor is powered directly by a high-voltage
electric motor, some of which go up to 400 volts. Less-common are
adjustable-swash-plate compressors, which adjust their output
without cycling.
Air Conditioning Compressor Basics
The typical car AC compressor is a 12-piston six-bore swash-plate
unit. The swash plate is mounted off-axis to the drive shaft,
“wobbling” as the shaft is driven by the EM clutch or electric
motor. Six double-ended pistons are oscillated by the swash
plate,each piston doing double-duty intake and compression. Reed
valves control the flow of refrigerant. A fine oil mist circulates
with the refrigerant, lubricating moving parts and sealing rubber
hoses and seals.
Compressor Maintenance
Because it is a sealed system, the only maintenance that the
typical AC compressor needs is regular use to keep lubricant
dispersed throughout the system. When addressing air conditioning
problems, refrigerant charge is important to consider, because
excessive or insufficient pressure may disable the system. Drive
belts need to be clean and tight for positive engagement. Finally,
electrical checks confirm proper function of pressure sensors and
switches; electromagnetic clutch fuse and relay; and the clutch
coil.Oil type and viscosity depend on the refrigerant and the
compressor. For example, R-134a compressors are lubricated by
polyalkylene glycol (PAG), which may not be compatible with
proprietary R-1234yf compressor oils. Viscosity is also important,
as lighter PAG 46 oils may not protect compressors requiring
heavier PAG 100 or PAG 150 oils.
Replacing an Air Conditioning Compressor
Air conditioning compressors can fail due to age, wear or neglect.
Many EM clutches are replaceable, but some EM-clutch and all
motor-driven compressors are replaced as an assembly. When changing
the AC compressor, such as with a re-manufactured air conditioning
compressor, use a recovery machine to extract refrigerant and
protect the atmosphere. On reassembly, ensure the proper charge of
refrigerant and oil for performance and reliability. These
specifications are in the repair manual.Fortunately, car air
conditioning isn’t overly complicated, but it is sensitive. If
you’re suffering AC problems, the AC compressor might be at the
root of them. Be sure to eliminate all other possibilities,
however, before delving into this sealed system.
