Refrigerant Circuit Pressures Specified Values, Vehicles without Heat Pump

Observe the test requirements. Refer to Pressures, Checking .

-- Pay attention to the pressure indicator (for example the pressure gauge) of the A/C service station.

NOTE:

The switching pressures for the activation of the Electrical A/C Compressor -V470- and the Radiator Fan -V7- /Radiator Fan 2 -V177- are vehicle-specific. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function for the A/C system and the battery regulation.

Pressures must be measured at the service connections; the component location for these connections are vehicle-specific. Refer to Refrigerant Circuit .

High-Pressure Side:

From the output pressure (when connecting the pressure gauge) raises up to maximum 20 bar (290 psi) pressure (depending on the ambient temperature and the operating conditions of the A/C system).

Low-Pressure Side:

Decreasing from initial pressure (when connecting the pressure gauges) to a value between 1.5 and 2.3 bar (21.76 to 33.36 psi) absolute pressure (depending on the required cooling output).

A/C Compressor Speed:

Depending on the required cooling output between 800 and 8500/min (currently a maximum of 5000/min for parked vehicles).

NOTE:

The temperature of the air downstream from evaporator, the current A/C compressor speed and the pressure of the refrigerant on the high pressure side depending on the vehicle are displayed by the different control modules (for example by the Front A/C Display Control Head -E87-, the Climatronic Control Module -J255-, the Thermal Management Control Module -J1024- or the A/C Control Module -J301-). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system and the battery regulation.

If a high cooling output is required (for example, a high outside temperature and the blower speed set on high), then the A/C compressor will not bring the pressure on the low pressure side to the required value (for example, for a certain time after turning on the A/C). The A/C compressor is not actuated at the maximum specified speed (of approximately 8500/min) on a stationary or slow moving vehicle (up to a speed of approximately 45 km/h (28 mph)) (the A/C compressor speed is limited to approximately 5000/min). After a vehicle reaches a speed of more than approximately 45 km/h (28 mph), the limit for the maximum permissible A/C compressor speed is lifted. At a A/C compressor speed of 5000/min, a high outside temperature and a high fresh air blower speed (inefficient environmental controls), the A/C compressor output (the delivery volume) is no longer sufficient to reduce the pressure on the low pressure side to the target value. To check the A/C compressor control under these conditions, for example, the fresh air blower is activated only with approximately 40% of the maximum voltage, check the pressures at a lower fresh air blower speed. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function for A/C system and the battery regulation. Refer to COOLING OUTPUT, CHECKING .

If there is a low cooling output (for example an exterior temperature of 20 °C (68 °F) and a low fresh air blower speed) the pressure on the high pressure side increases only to a value of 6 to 7 bar (87 to 101.5 psi) (the absence of energy is low, the refrigerant is quickly cooled in the condenser). To check the A/C compressor control and the pressure in the refrigerant circuit under these conditions for example the activating the fresh air blower with maximum voltage, adjusting the A/C system to maximum heat output and recirculating air mode. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system. Refer to COOLING OUTPUT, CHECKING .

Under unfavorable conditions (very high ambient temperatures, high humidity), pressure on high-pressure side may increase to max. 29 bar (421 psi).

The specified speed of the A/C compressor depending on the vehicle is displayed from different control modules (for example by the Front A/C Display Control Head -E87-, Climatronic Control Module -J255- or the A/C Control Module -J301-). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system.

The measured high pressure from different sensors (for example from the High Pressure Sensor -G65-, from the Refrigerant Circuit Pressure Sensor -G805- or the A/C Pressure/Temperature Sensor -G395-) is displayed by the vehicle (for example from the Front A/C Display Control Head -E87-, the A/C Control Module -J301-, the Thermal Management Control Module -J1024- or the Climatronic Control Module -J255-). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system.

Depending on the A/C compressor speed and the control characteristic of the expansion valve, the low pressure settles within the A/C compressor output range in the tolerance range (1.5 to 2.3 bar (1.5 to 33.36 psi) positive pressure).

The specified speed of the A/C compressor must for this test be greater than 1500 RPM. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C compressor.

In setting "maximum cooling output" the target speed of the A/C compressor is regulated to approximately 4000 up to 5000/min. This value is vehicle-specific and is displayed as the measured value from the corresponding control module (for example from the display control head, the Front A/C Display Control Head -E87-, Climatronic Control Module -J255- or the Thermal Management Control Module -J1024-). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function for the A/C system and the battery regulation.

At absolute pressure, 0 bar (0 psi) corresponds to absolute vacuum. Normal ambient pressure corresponds to 1 bar (14.5 psi) absolute pressure. On the scales of most pressure gauges, 0 bar (0 psi) corresponds to an absolute pressure of 1 bar (14.5 psi) (can be seen from -1 bar (-14.5 psi) mark below 0). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function for the A/C System.

If, for a vehicle with two evaporators (one in the heater and A/C unit and one for battery cooling), the measured temperature on one of the evaporators corresponds to the specified value or the specified value falls short, but does not reach the required specified value on the other evaporator, the following adjustment is performed: the corresponding control module (for example battery regulation control module or the thermal management control module) activates the electric A/C compressor with increased speed (thereby increasing the A/C system cooling output and decreasing the pressure on the low pressure side as well as the evaporator temperature) via additional control modules (for example the electric drive power and control electronics and the A/C compressor control module). If on the evaporator the specified value for the temperature falls short, the corresponding control module (for example the battery regulation control module) activates the shut-off valve (for example the refrigerant shut-off valve 1 or the refrigerant shut-off valve 2) so that no more refrigerant flows through the evaporator which is too cold. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system and the battery regulation. Refer to COOLING OUTPUT, CHECKING and Component Location Overview - A/C System .

Because the output of the evaporator in the battery cooling module is noticeably smaller than the output of the evaporator in the heater and A/C unit, because of too little refrigerant in the circuit the required specified temperature in the battery cooling module may be reached but the specified temperature in the heater and A/C unit is no longer reached (although the A/C compressor is activated with a higher speed). Refer to COOLING OUTPUT, CHECKING and Refrigerant Circuit .

Possible Deviation from Specified Value, the Cause and its Elimination
The required cooling output is not attained in the heater and A/C unit evaporator (and in the evaporator for battery cooling module). High pressure remains constant or increases only slightly (above pressure with engine stopped). Low pressure quickly drops to target value or lower.		Refer to Possible Deviation From Specified Value During The Pressure Test (1 Of 11)
The required cooling output is reached at first in the evaporator in the heater and A/C unit (and in the evaporator for battery cooling) after some time or after a longer running time the cooling output is no longer sufficient. The high pressure and low pressure are normal. After some time the high pressure raises above the specified value, the low pressure corresponds to the specified value or it falls under the specified value.		Refer to Possible Deviation From Specified Value During The Pressure Test (2 Of 11)
The required cooling output is not attained in the heater and A/C unit evaporator (and in the evaporator for battery cooling). The high pressure pipe corresponds to the specified value The low pressure is too low (lower than the target value)		Refer to Possible Deviation From Specified Value During The Pressure Test (3 Of 11)
The A/C compressor noise (particularly after switch-on) The required cooling output is not attained in the heater and A/C unit evaporator and/or in the evaporator for battery cooling. High pressure normal or too high Low pressure too high (the specified value is not reached,		Refer to Possible Deviation From Specified Value During The Pressure Test (4 Of 11)
The required cooling output is not attained in the heater and A/C unit evaporator (and in the evaporator for battery cooling). High pressure and low pressure are normal (correspond to the specified value)		Refer to Possible Deviation From Specified Value During The Pressure Test (5 Of 11)
The required cooling output is not attained in the heater and A/C unit evaporator (and in the evaporator for battery cooling). The high pressure pipe corresponds to the specified value The low pressure corresponds to the specified value or is too low		Refer to Possible Deviation From Specified Value During The Pressure Test (6 Of 11)
The required cooling output is not attained in the heater and A/C unit evaporator (and in the evaporator for battery cooling). The high pressure pipe corresponds to the specified value Low pressure quickly drops to specified value or lower.		Refer to Possible Deviation From Specified Value During The Pressure Test (7 Of 11)
The required cooling output is not attained in the heater and A/C unit evaporator (and in the evaporator for battery cooling). The required cooling output is only not attained at the heater and A/C unit evaporator (the cooling output on the evaporator for the cooling output is OK). The high pressure only falls slightly (via the pressure with the engine stopped) or corresponds to the specified value. Low pressure quickly drops to target value or lower.		Refer to Possible Deviation From Specified Value During The Pressure Test (8 Of 11)
The required cooling output is not attained in the heater and A/C unit evaporator (and in the evaporator for battery cooling). The high pressure increases above specification Low pressure quickly drops to specified value or lower.		Refer to Possible Deviation From Specified Value During The Pressure Test (9 Of 11)
The required cooling output is only not attained at the evaporator for the battery cooling module components (the cooling output at the heater and A/C unit evaporator is OK). The high pressure corresponds to the specified value or increases only slightly (above pressure with engine stopped). Low pressure drops to specified value or lower.		Refer to Possible Deviation From Specified Value During The Pressure Test (10 Of 11)
The required cooling output is not attained in the heater and A/C unit evaporator (and in the evaporator for battery cooling). The high pressure does not increase or only increases slightly above pressure with engine stopped. The low pressure does not drop or drops only slightly.		Refer to Possible Deviation From Specified Value During The Pressure Test (11 Of 11)