A/C Compressor
Design, A/C compressor 7SB16C
Purpose
The A/C compressor (A9) is responsible for sucking in and compressing the refrigerant.
Function
After the electromagnetic clutch (A9k1) has completed the flow of power between the vehicle engine and A/C compressor the drive shaft (1) propels the swash plate (3). The pistons (4) move up and down due to the location of the swash plate (3) set at an angle. During the intake stroke gaseous refrigerant is sucked in through the intake valve (6).
When the piston (4) moves in the opposite direction it pumps the gaseous refrigerant through the outlet valve (7) into the refrigerant line to the condenser whereby it is compressed and heated up. With the 7SB16C model A/C compressor the volume of the gaseous refrigerant is regulated by the regulation valve (8.1) in the A/C compressor.
Volume regulation on A/C compressor 7SB16C
At low engine speeds the efficiency of the air conditioning is reduced highly due to the low speed of the A/C compressor and the reduced cooling of the refrigerant in the condenser. This situation increases the heat load. The A/C compressor is therefore designed so that its capacity is sufficient even at low speeds. At increasing engine and vehicle speed the heat load decreases and the capacity of the A/C compressor increases. To prevent the A/C compressor from consuming power from the engine unnecessarily and still maintain the refrigerant circuit, the output from the A/C compressor is reduced from a maximum of 100 % to a minimum of 5 %.
Function
A = High pressure
B = Crankcase chamber pressure
C = Intake pressure
100 % output (I)
The conditions for 100 % output are either constant low speed or high heat load or both. The high intake pressure C causes the regulation valve to close so that no vapor flows between the outlet opening and crankcase chamber. Refrigerant always flows through the connection duct between the crankcase chamber and intake opening. For this reason nearly the same pressure B is present in the crankcase as on the intake side C. This moves the swash plate into the position for maximum volume. The swash plate angle in relation to vertical is at its maximum. This provides a large piston stroke.
From 100% to 5% output (II)
If the control variables change, i.e. the heat load decreases or engine speed increases, the pressure on the intake side C decreases allowing the regulation valve to open. Now compressed refrigerant flows from the outlet opening to the crankcase. The pressure in tile crankcase B increases causing the swash plate to reduce its angle resulting in a reduction of the output.
Function
A = High pressure
B = Crankcase chamber pressure
C = Intake pressure
5 % output (III)
If the engine speed is high or the heat load low, the intake pressure C is at a constant low value which holds the regulation valve open.
Refrigerant flows from the high pressure side A to the crankcase. The pressure in the crankcase B reaches a maximum. This forces the swash plate to move to a position allowing only minimum output. The angle of the swash plate in relation to vertical is at its minimum. This results in a small piston stroke.
From 5 % to 100 % output (IV)
If the conditions change again, i.e. the heat load increases or the engine speed decreases, the intake pressure C increases. Refrigerant no longer flows between the outlet opening and the crankcase.
Due to the uniform flow from the crankcase to the intake opening through the connection duct the high pressure A reaches nearly the same level as the intake pressure C causing the swash plate angle to increase thereby increasing the output until the maximum is reached.