P83.55-2004-06
1 Main control valve
2 Auxiliary control valve
3 Swash plate
4 Compression chamber
5 Crankcase
7 Magnetic coil
8 Pulley
9 Pressure plate
10 Piston
11 Spring
A9/1 Speed sensor
Operation of internal control
The A/C compressor has a single-acting swash plate (3) with variable pitch angle and 6 axial cylinders. The required quantity is achieved by changing the angle of the swash plate. The position of the swash plate (3) depends on the pressure difference between the "pressure above the piston" and "the pressure below the piston".
The main control valve (1) increases or decreases the pressure in the crankcase (5) depending on the intake pressure. This changes the pitch angle of the swash plate (3) adjusting the piston (10) to the required stroke. The auxiliary control valve (2) allows the compressor to react to quick load changes.
P83.55-2005-06
Illustrated with swash plate (3) "11% capacity" position
1 Main control valve
3 Swash plate
11 Spring
Control at 100% capacity
A constant low speed, high refrigeration requirement or both are necessary for 100% output. In this case, the intake pressure is high causing the main control valve (1) to close. This means that the pressure in the crankcase is virtually the same as on the intake side. This allows the spring (11) to move the swash plate (3) to the position for maximum output.
Control between 100% and 11% capacity
When driving on a freeway or for longer trips at high engine speed or vehicle speed, the refrigeration capacity required decreases. This causes the pressure on the intake side to decrease allowing the main control valve (1) to open. This allows gaseous refrigerant to flow from the outlet opening to the crankcase increasing the pressure on the bottom of the piston and reducing the angle of the swash plate (3) against the force of the spring, resulting in a decrease in the output.
P83.55-2006-06
Illustrated with swash plate (3) "100 % capacity" position
1 Main control valve
2 Auxiliary control valve
3 Swash plate
10 Piston
11 Spring
Control at 11% capacity
At constant temperature in the passenger compartment (e.g. uniform speed over longer time), the refrigeration capacity required is low. The intake pressure is low causing the main control valve (1) to open. High pressure is transferred to the crank- case through the open main control valve (1). This high pressure acts on the bottom of the piston, pressing the piston (10) in the direction of the valve plate/cylinder head. The angle of the swash plate (3) is reduced via the piston rod.
A small swash plate angle results in a small stroke=low output. The auxiliary control valve limits the pressure in the crankcase.
Control between 11% and 100% capacity
The conditions change again. The intake pressure increases causing the auxiliary control valve (2) and main control valve (1) to close.
The pressure in the crankcase is therefore nearly the same as on the intake side. This allows the spring (11) to move the swash plate (3) into the position for maximum output.