Display Group 001

Display Group 001

A/C compressor regulator valve (N280 ) and high pressure sensor (G65)

• If a compressor shutoff condition exists for the compressor. Refer to => [ Display Group 002 ] , the A/C compressor regulator valve (N280) cannot be activated, not even during the output diagnostic test mode. Refer to => [ Final Control Diagnosis ] Final Control Diagnosis.

• If no pressure signal is detected by High Pressure Sensor (G65), A/C Compressor Regulator Valve ( N280) must not be activated.





• Display field "1" shows the current strength flowing over the A/C compressor regulator valve (N280).

• The current strength is calculated by the Climatronic control module (J255) A/C control head. It depends on the required cooling output, the selected (set) operating mode of the Climatronic control module (J255) A/C control head and the vehicle electrical system voltage. Reliable regulator valve control requires a predefined minimum current of 0.3 A for currently installed regulator valves.

• If the A/C compressor regulator valve (N280) is completely activated, a maximum current of approx. 0.65 A (up to 0.8 A) is set depending on the vehicle electrical system voltage and the version of the Climatronic control module (J255) A/C control head (calculated, regulated, and restricted by the Climatronic control module (J255) A/C control head).

• If the pressure changes in the refrigerant circuit (display field " 3" and "4") while the engine is running even though the A/C compressor regulator valve (N280) is activated with maximum current, check the belt pulley/drive unit at the compressor. The compressor must be driven (if the overload protection was triggered, the belt pulley is moving but the compressor is not being driven, for example).





• Display field "2" shows the duty cycle for the time during which current can actually flow.

• The Climatronic control module (J255) A/C control head operates with a frequency of 500 Hz (500 Hertz = 500 switch-on pulses per second). The duty cycle indicates the activation time per pulse.

• The activation signal can be checked for example by the Vehicle Diagnosis, Testing and Information System (VAS 5051A) in the "measurement" function. Refer to => [ A/C Compressor Regulator Valve, Checking Activation Signal ] Climatronic Control Module A/C Control Head Electrical Test.

• The duty cycle is selected by the Climatronic control module (J255) A/C control head so that the evaporator target temperature which depends on various influences is achieved by the evaporator vent temperature sensor (G263). Refer to => [ Display Group 009 ].

• If a fault is identified at the evaporator vent temperature sensor (G263), the Climatronic control module (J255) A/C control head switches to emergency operation and the A/C compressor regulator valve (N280) is activated only with a maximum control current defined by the software of the Climatronic control module (J255) A/C control head. The maximum control current depends on the version of the Climatronic control module (J255) A/C control head. For the currently installed Climatronic control module (J255) A/C control heads, it can be approx. 0.3 A to 0.5 A (as a result the cooling output of the A/C system is lower and is no longer sufficient at high temperatures).





• Display field "3" shows the duty cycle for the time during which the signal is actually present.

• The Climatronic control module (J255) A/C control head calculates the pressure in the refrigerant circuit via the duty cycle; the calculated pressure is displayed in display field "4".

• At a duty cycle less than 12 % (corresponds approximately 1.8 bar absolute pressure) and greater than 87.5% (corresponds approximately 32 bar absolute pressure), A/C control head Climatronic Control Module ( J255) does not switch on the compressor (A/C Compressor Regulator Valve (N280) is not activated). Compressor is only switched on again after duty cycle has become greater than 15 % (corresponds to 2.6 bar absolute pressure) or less than 48% (corresponds to 16 bar absolute pressure).

• If the pressure in the refrigerant circuit or the engine coolant temperature is too high, A/C control head Climatronic Control Module ( J255) regulates the compressor performance (to avoid sudden compressor cut-off):

• - As soon as pressure in refrigerant circuit exceeds 30 bar (absolute pressure), full compressor performance is only enabled again after pressure has become less than 16 bar.

• - As soon as coolant temperature exceeds 115° C (full shutdown at 118° C).

• Depending on the duty cycle, a signal is sent from the Climatronic control module (J255) A/C control head via the comfort data bus system to the respective engine control module so that it switches the coolant fan(s) (V7) via the coolant fan control module (J293).

• Depending on the version of the Climatronic control module (J255) A/C control head, the coolant fan is switched on immediately in A/C system mode when the compressor is switched on or the coolant fan is only activated when a pressure of approx. 9 bar is exceeded in the refrigerant circuit.

• In terms of absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure equals approximately 1 bar absolute pressure. 0 bar pressure corresponds to an absolute pressure of one bar on most pressure gauges (indicated by "-1" below "0").

• Pressure in the refrigerant circuit and thus the duty cycle is governed by various factors of influence. However, it is generally true that the pressure is not greater than 20 bar (absolute pressure) at maximum compressor output and an ambient temperature of 20 to 25°C. Due to high coolant output, pressures up to 30 bar (absolute pressure) may occur under extreme operating conditions (e.g. in southern countries with high ambient temperatures, " stop and go traffic " and high humidity).

• The high pressure sensor (G65) functions with a frequency of 50 Hz (50 Hertz = 50 activation pulses per second). The duty cycle indicates the activation time per pulse.

• The activation signal can be checked for example by the Vehicle Diagnosis, Testing and Information System (VAS 5051A) in the "measurement" function. Refer to => [ High Pressure Sensor Pressure Signal ] Climatronic Control Module A/C Control Head Electrical Test (check the signal from the high pressure sensor (G65)).

• The signal generated by the high pressure sensor ( G65) is also used for controlling the engine (the torque necessary for the compressor drive depends on the pressure in the refrigerant circuit). Depending on the engine control module version, the signal is displayed as the duty cycle in the measured value block of the respective engine control module.

• The signal that is transferred when the pressure in the refrigerant circuit is approximately 5 to 6 bar corresponds to an approximate duty cycle of 22% (with compressor not engaged, an ambient temperature of 20°C and a properly filled refrigerant circuit).





• Also observe the information regarding display field "3"

• A/C control head Climatronic Control Module (J255 ) calculates pressure in refrigerant circuit via the duty cycle (display field "3").

• If refrigerant circuit has been correctly filled, pressure will be 2.6 bar at a temperature of -3 C°. To avoid fault entries at low temperatures, the Climatronic control module (J255) A/C control head recognizes a fault in the refrigerant circuit first at a pressure less than 1.8 bar (attained at -12 C°). However, at this temperature the High Pressure Sensor (G65) is no longer checked.

• If the pressure changes in the refrigerant circuit (display field " 3" and "4") while the engine is running even though the A/C compressor regulator valve (N280) is activated with maximum current, check the belt pulley/drive unit at the compressor. The compressor must be driven (if the overload protection was triggered, the belt pulley is moving but the compressor is not being driven, for example).