Mercedes-Benz ML320. Manual — part 686

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

Fig. 111: Identifying Refrigerant Compressor Control Valve, Function (2 Of 2)

Control at max. swept volume

(e.g. at higher ambient temperature or higher cooling capacity requirement)

If the suction pressure (Ps) rises above the diaphragm pressure (Ps1) in the refrigerant compressor control valve
and the control current is increased at the same time, in the refrigerant compressor control valve the passage -
high pressure (Pd) to crankcase pressure (Pc) - is closed by the control plunger (2). The crankcase pressure (Pc)
drops, as no refrigerant flows from the high pressure side into the crankcase via the refrigerant compressor
control valve.

In the long-term the bypass (1) sets up a pressure compensation between the suction pressure (Ps) and crankcase
pressure (Pc), i.e. the sum of the reaction forces on the left side, resulting from the crankcase pressure (Pc),
return force of the swash plate (centrifugal force) and the spring return force, is therefore smaller than the sum
of the piston forces. The swash plate angle extends to beyond the "0-position ", i.e. the inclined position
increases continuously to the swash plate's mechanical limit stop at the stop plate. The piston stroke increases
linear to the swash plate's inclination till it reaches max. volumetric flow.

CONTROL VALVE, LOCATION/TASK/FUNCTION - GF83.55-P-2102P

ENGINE 111, 112, 113, 271, 272, 611, 612, 642, 646 in MODEL 203.0 /2 with CODE (580) Air
conditioning (or Tempmatic for USA) with CODE (580) Automatic air conditioning with CODE (581)
Automatic air conditioning with CODE (581) Comfort automatic air conditioning

2001 Mercedes-Benz ML320

1998-2005 HVAC Climate Control - 163 Chassis

me

ENGINE 111, 112, 271, 272, 611, 612, 646 in MODEL 203.7 with CODE (580) Air conditioning (or
Tempmatic for USA) with CODE (580) Automatic air conditioning with CODE (581) Automatic air
conditioning with CODE (581) Comfort automatic air conditioning

ENGINE 112.942 /970, 113.942 /965 /981, 612.963, 628.963 in MODEL 163 as of 1.9.01 with CODE (580)
Automatic air conditioning

ENGINE 112, 113, 271, 272, 273, 612, 642, 646 in MODEL 209.3

ENGINE 112, 113, 271, 272, 273, 642 in MODEL 209.4

Shown on model 203

Fig. 112: Identifying Refrigerant Compressor Control Valve And Compressor - Shown On Model 203

BELT PULLEY, FUNCTION - GF83.55-P-2103-02P

Function under normal operating conditions

Under normal operating conditions the rubber (2) is deformation resistant. Thus it transmits the belt pulley's (3)
torque to the hub (1) and at the same time to the refrigerant compressor shaft, whereby the hub (1) and belt
pulley (3) turn in the direction of the arrow.

The refrigerant compressor torque < the rubber torque limit (2). In this operating condition, the rubber (2) acts
as a shock absorber by inhibiting resonance via the belt with other engine components.

Refrigerant compressor
control valve, position

The refrigerant compressor control valve (1) is located on the
refrigerant compressor (A9).

Refrigerant compressor
control valve, task

The refrigerant compressor control valve (1) regulates the swept
volume of the refrigerant compressor (A9) dependent upon the
refrigerant capacity requirement.

Refrigerant compressor
control valve, function

GF83.55-P-
2102-02P

2001 Mercedes-Benz ML320

1998-2005 HVAC Climate Control - 163 Chassis

me

Fig. 113: Identifying Belt Pulley, Function - Function Under Normal Operating Conditions

Function of refrigerant compressor lock up

When the refrigerant compressor locks up, the torque required to drive the refrigerant compressor must be
greater than the torque present on the belt pulley (3). This causes slip to occur between the belt pulley (3) and
hub (1) because of the deformation and wear of the rubber (2). Thus the belt pulley (3) continues to rotate even
with a locked up refrigerant compressor.

The refrigerant compressor torque > the rubber torque limit (2).

In this operating condition, the rubber (2) acts as a belt pulley protection device.

Fig. 114: Identifying Belt Pulley, Function - Function Of Refrigerant Compressor Lock Up

BELT PULLEY, DESIGN - GF83.55-P-2103-03P

The belt pulley (3) is attached to the hub (1) via the rubbers (2), the hub (1) being firmly connected to the
refrigerant compressor shaft.

2001 Mercedes-Benz ML320

1998-2005 HVAC Climate Control - 163 Chassis

me