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A/C Compressor Operation
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| A/C Compressor Operation |
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| Updated |
Jul 7, 2004 20:29:16 |
| Rating |
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Description:
Below is an overview of an A/C compressor and its operation
The Compressor
The compressor used to air condition your car works in a
similar way to the one in the refrigerator in your kitchen. The job of the
compressor is to move liquid refrigerant around in a pipe. The compressor
pumps, or forces, the liquid from the evaporator into a condenser and
expansion valve, and then back to the evaporator.
There are three common types of
compressors:
Â
Two cylinder reciprocating piston type
Four cylinder RADIAL type
Six cylinder AXIAL type The engine drives the compressor with a belt. In action, the
compressor takes the low pressure refrigerant from the evaporator and
compresses it according to speed and air temperature. The inlet side is
known as the low (pressure) side and the outlet side is known as the high
(pressure) side.
The compressor compresses the refrigerant, and raises its
temperature higher than that of the surrounding air. Then, the compressor
forces the refrigerant into the condenser.
Compressor Clutch
The air conditioning compressor has an electromagnetic
clutch that can engage or disengage the compressor pulley. The compressor
pulley always turns when the engine is running, but the compressor only
runs when the pulley is engaged to the compressor driving shaft.
When this system is activated, current runs through the
electromagnetic coil. The current attracts it to the armature plate. The
strong magnetic pull draws the armature plate against the side of the
turning pulley. This locks the pulley and the armature plate together; the
armature plate drives the compressor.
When the system is deactivated, and current stops running
through the electromagnetic coil, flat springs pull the armature plate
away from the pulley.
The magnetic coil does not turn since its magnetism is
transmitted through the pulley to the armature. The armature plate and hub
assembly are fastened to the compressor drive shaft. When it's not driving
the compressor, the clutch pulley turns on a double row of ball
bearings.
AC Compressor Drive Ring
Inside the air conditioner's refrigerant compressor is a
drive ring made of a friction material that is mounted to both sides of
the "swash" or "wobble" plate. As the swash plate rotates, the friction
material pushes the ball bearings (mounted to the pistons) back and
forth.
The Condenser
The condenser is a long tube that goes back and forth
through a multitude of cooling fins, quite similar to the evaporator in
structure. The condenser is mounted in front of the radiator to take
advantage of the forced air provided by the fan and the motion of the
car.
As the highly pressurized refrigerant (vapor) flows into
the condenser, it gives off heat and warms the condenser. This causes the
condenser to be hotter than the forced air coming through the condenser.
The condenser hands its heat off to the forced air and turns the
refrigerant back into cool liquid in the expansion valve, where it heads
back to the evaporator.
The Evaporator
The evaporator is a long tube, or coil, that goes back
and forth through a multitude of cooling fins. It is quite similar to the
condenser in structure.
The refrigerant is a liquid when it enters the
evaporator. A fan blows warm air over the evaporator. The warm air causes
the liquid refrigerant to boil. This means that it absorbs the heat from
the warm air. Once it has absorbed the heat from the warm air, the warm
air isn't warm anymore. The same blower that blows the warm air (that is
now "cool" air) over the evaporator, keeps on blowing it into the interior
of your car, and you have -- air conditioning!
The evaporator also removes the moisture from the air
coming through its fins and turns it into water. The water just drains
off.
The temperature of the evaporator coil can go from 33
degrees F to 0 degrees F. If it goes below 32 degrees F, the moisture
that's supposed to drain off the coils will freeze. This makes for a very
(surprise!) inefficient system, so a thermostatic switch is used to
connect and disconnect it to the compressor as necessary.
Expansion Valve
The expansion valve determines the correct amount of
refrigerant going into the evaporator, and it lowers the pressure of the
refrigerant.
When the compressor starts, the expansion valve opens and
the liquid refrigerant flows through a strainer in the high pressure
liquid inlet. Once in the expansion valve, the refrigerant is correctly
pressurized. As the evaporator calls for more refrigerant, the expansion
valve allows the required amount of low pressure liquid refrigerant into
the coils.
The expansion valve maintains the delicate balance
between the heat load and the cooling efficiency of the evaporator.
Discharge/Suction Service Valves
Discharge and suction service valves allow the air
conditioning system to be emptied and filled. These valves also provide
places where the system can be checked with pressure gauges.
Note: Some systems use a Schrader valve in place
of the discharge and suction valves. This is a spring-loaded valve which
looks rather like the valve in a tire.
The Compressor Relay
A capillary tube from a cycling switch lets the switch
know what the temperature is in the evaporator. This switch turns the
compressor on and off to keep the evaporator temperature at about 32 to 45
degrees F. The relay switch keeps moisture from freezing on the evaporator
core.
Electric Air Conditioning Fan
Sometimes an extra electric fan is placed in front of the
condenser to provide an extra flow of air during warm weather, or for
times when the car has to idle for a long time. You activate and
deactivate the air conditioning fan when you turn it on and off at the
control panel.
Compressor Belt
The compressor is engine driven by a belt on the front of
the crankshaft. |
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