Fig. 110: Identifying Refrigerant Compressor Control Valve, Function (1 Of 2)
Variable volume control in partial load range
(e.g. at low ambient temperature or low cooling capacity requirement)
Essentially, the cooling output is dependent on the intake pressure, i.e. if the suction pressure (Ps) drops below
the diaphragm pressure (Ps1) in the refrigerant compressor control valve and the regulating current is reduced at
the same time, then the passage from high pressure (Pd) to crankcase pressure (Pc) is released by the control
plunger (2) in the refrigerant compressor control valve. As a result, refrigerant flows from the high pressure side
into the crankcase which results in an increase in crankcase pressure (Pc).
The sum of the forces on the left-hand side, resulting from the crankcase pressure (Pc), the return force
(centrifugal force) of the swash plate and the spring return force thus becomes greater than total piston forces.
The swash plate moves into a vertical position, which causes a reduction in piston travel and replacement
volume.
In addition, a regulation of the cooling output takes place as a function of the air humidity, i.e. at high air
humidity there is an external actuation of the control valve, achieving a post-regulation of the cooling output
(preventing fogging up of the windows).
The refrigerant compressor is automatically switched off at a volumetric flow of less than 5 cm
3.
2001 Mercedes-Benz ML320
1998-2005 HVAC Climate Control - 163 Chassis
me
Saturday, October 02, 2010 3:23:16 PMPage 131 © 2006 Mitchell Repair Information Company, LLC.
