Mechanically Driven A/C Compressor, Checking Pressure With A/C System Switched On
Pressures, Checking. Refer to PRESSURES, CHECKING .
Specified Values for the Refrigerant Circuit Pressures. Refer to PRESSURES, CHECKING .
Pressures, Checking
Refrigerant circuit with expansion valve, receiver/dryer with or without A/C Clutch -N25- and A/C Compressor Regulator Valve -N280- (with an A/C compressor regulated from the outside)
Connect the A/C Service Station. Refer to A/C SERVICE STATION ON REFRIGERANT CIRCUIT, CONNECTING .
If a malfunction occurs at only one evaporator in vehicles with two evaporators, check pressures in the refrigerant circuit; if they are OK, check line connection between malfunctioning evaporator and line connection end at distribution point of refrigerant lines (for constrictions or blockage). If no malfunction can be determined, empty the refrigerant circuit and refill with the specified refrigerant quantity. Then check the pressures and the A/C system cooling output again; if the complaint still exists, replace the expansion valve that is prematurely switched by the questioned evaporator. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
Refer to
Test Requirements
- The A/C Service Station in connected to the refrigerant circuit. Refer to A/C SERVICE STATION ON REFRIGERANT CIRCUIT, CONNECTING .
- Pay attention to the test requirements for checking the pressures in the refrigerant circuit with the ignition switched off. Refer to.
- The pressures in the refrigerant circuit with the ignition turned off meet the specifications. Refer to.
- Pay attention to the test requirements for checking the cooling output. Refer to REPAIR INFORMATION .
The switching pressures for the activation of the A/C Compressor Regulator Valve -N280-, the A/C Clutch -N25- (if equipped) and the Radiator Fan -V7- are vehicle specific. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
Pressures must be measured at the service connections; the component location for these connections are vehicle-specific. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
- The engine is warm (at an ambient temperature below 25 °C (77 °F)).
If the engine is not warm perform a road test.
For the cooling output test the engine must be warm but at an ambient temperature smaller than 25 °C (77 °F) a specific A/C system cooling output it is necessary that the engine and lower ambient temperatures are warm.
-- Start the engine.
-- Adjust the A/C system to maximum cooling output. Refer to REPAIR INFORMATION .
- The A/C compressor is actually being driven with the engine running (visual inspection. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
- The A/C Compressor Regulator Valve -N280- is activated. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function for the A/C system.
The A/C compressor is driven by different components depending on the engine (belt or input shaft). The belt pulley or the drive unit has an overload protection to protect these components and the engine, if the A/C compressor is runs with resistance. Refer to A/C COMPRESSOR . .
On vehicles with A/C Compressor Regulator Valve -N280- the control current can be read out in the measured values. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function for the A/C system.
If A/C compressor is not driven with the engine running or regulating valve is not actuated:
-- Determine and eliminate cause for example by checking air conditioner DTC memory. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
-- If equipped, check the power supply for the A/C Clutch -N25- if this is OK, service the A/C clutch. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
-- Check the activation of the A/C Compressor Regulator Valve -N280-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
On A/C compressors with a A/C Clutch -N25- the A/C compressor only works (delivers refrigerant) when near the A/C Compressor Regulator Valve -N280- the A/C Clutch -N25- is also activated. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
The A/C Compressor Regulator Valve -N280- (and the A/C Clutch -N25-) is activated by the A/C Control Module -J301-, from the Front A/C Display Control Head -E87- or the Climatronic Control Module -J255- or a downstream control module. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
All of the test requirements marked with a * are vehicle-specific and described in the repair information belonging to the vehicle. Refer to REPAIR INFORMATION and REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
- Radiator and condenser are clean (if necessary clean)*. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
- The heat shield insulation on the expansion valve is OK and installed correctly*. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
- Ribbed belt is OK and properly tensioned. Ribbed belt for A/C compressor and generator are OK and correctly tensioned.* Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT and REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
- The drive unit and the A/C compressor is OK and installed correctly.* Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT and REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
- All air guides, covers and seals are OK and correctly installed*. Refer to REFRIGERANT CIRCUIT .
- The A/C system diagnostic does not detect any malfunctions (when the engine is running and the A/C system is switched on), and no compressor shut-off condition is displayed in the measured values of the corresponding control module (only for vehicles with "A/C system" diagnostic).* Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function for the A/C system.
- Air flow through dust and pollen filter not obstructed by dirt* Refer to REFRIGERANT CIRCUIT .
- The heater and A/C unit does not draw in any secondary air at the highest fresh air blower speed. The evaporator and the heater not drawing in secondary air at maximum fresh-air blower speed.* Refer to REFRIGERANT CIRCUIT .
- The air doors in the heater and A/C unit, in the heater and in the evaporator reach their end position.* Refer to REPAIR INFORMATION . and REFRIGERANT CIRCUIT .
- The fresh air intake ducts under the hood and in the vehicle interior and the corresponding water drain valves are OK.* Refer to REPAIR INFORMATION and REFRIGERANT CIRCUIT .
- The engine is warm.
- Vehicle is not exposed to direct sunlight. Refer to REPAIR INFORMATION .
- The ambient temperature is greater than 15 °C (59 °F).
- All instrument panel vents are open.* Refer to AIR DUCT or Air Conditioning .
Adjustment for example on the Front A/C Display Control Head -E87- or the Climatronic Control Module -J255- or the A/C Control Module -J301- (and the Rear A/C Display Control Head -E265- on vehicles with two heater and A/C units)*. Refer to REPAIR INFORMATION . and COMPONENT LOCATION OVERVIEW - A/C SYSTEM . .
Adjustment on the Front A/C Display Control Head -E87- /Climatronic Control Module -J255- *. Refer to REPAIR INFORMATION . and REFRIGERANT CIRCUIT .
-- Preselect "Auto" mode (A/C compressor on).
-- Set temperature pre-selector switch to "cold" or "LO" for driver's side and front passenger's side (and left and right rear seats in vehicles with two heater and A/C units).
Adjustment on the A/C Control Module -J301- *:
-- Press A/C button and Rec- or recirculated air button.
-- Turn rotary temperature control towards "cold" stop.
-- Position the fresh-air blower dial in the position "4" (maximum fresh air blower speed).
The following system test conditions should be met:
- The Radiator Fan -V7- is operated or the Radiator Fan -V7- and Radiator Fan 2 -V177- runs (minimum in 1 step).* Refer to REPAIR INFORMATION and REFRIGERANT CIRCUIT .
On specific versions the fan is switched on after the refrigerant circuit pressure specified value is exceeded. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
- Fresh Air Blower -V2- (and Rear Fresh Air Blower -V80- in vehicles with two heater and A/C units) running at maximum speed.*
- The coolant shut-off valve is closed.* Refer to REPAIR INFORMATION . and COMPONENT LOCATION OVERVIEW - A/C SYSTEM .
- The pump/valve unit valves are closed and there is no coolant circulation pump delivery.* Refer to REPAIR INFORMATION . and COMPONENT LOCATION OVERVIEW - A/C SYSTEM ..
- Fresh Air Blower -V2- (and Rear Fresh Air Blower -V80- in vehicles with two heater and A/C units) running at maximum speed.*
- Recirculated/fresh-air door set to "Recirculated air mode" (within one minute, after starting vehicle, air-flow door is closed and recirculated-air door is opened)*
- The coolant shut-off valve is closed.*
- The valves of pump/valve unit are closed and there is no coolant circulation pump delivery.*
Specified Values for the Refrigerant Circuit Pressures
- Pay attention to the test requirements and check the pressure. Refer to PRESSURES, CHECKING .
Checking:
-- Bring the engine speed up to 2000 RPM.
-- Pay attention to the pressure indicator (for example the pressure gauge) of the A/C Service Station. Refer to the A/C Service Station service/repair/system information.
The switching pressures for the activation of the A/C Compressor Regulator Valve -N280- and the radiator fan are vehicle-specific. use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function for the A/C system.
Pressures must be measured at the service connections; the component location for these connections are vehicle-specific. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT
High-Pressure Side:
Increasing from initial pressure (when connecting the pressure gauges) to a maximum of 20 bar (290 psi).
Low-Pressure Side:
Decreasing from initial pressure (when connecting the pressure gauges) to a value between 1.5 and 2.3 bar (21.8 and 33.4 psi) absolute pressure (depending on the required cooling output).
If high cooling output is needed (for example, the outside temperature is very high, the blower speed it set on high but the engine speeds are low), then the A/C compressor will not bring the pressure on the low pressure side to the specified value (for example, for a certain time after turning on the A/C). The A/C compressor is actuated with maximum specified control current, however delivery volume is no longer sufficient at this engine speed to reduce pressure on low-pressure side to the specified 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 output (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. Refer to REPAIR INFORMATION .
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 102 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 REPAIR INFORMATION .
Under unfavorable conditions (very high ambient temperatures, high humidity), pressure on high-pressure side may increase to max. 29 bar (420 psi).
The specified operating current for the A/C Compressor Regulator Valve -N280- is displayed as the measured value of the Front A/C Display Control Head -E87-, the A/C Control Module -J301- of the Climatronic Control Module -J255-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
The measured high pressure from the High Pressure Sensor -G65-, from the Refrigerant Circuit Pressure Sensor -G805- or the A/C Pressure/Temperature Sensor -G395- is displayed as the measured value of the Front A/C Display Control Head -E87-, the A/C Control Module -J301- or the Climatronic Control Module -J255-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
Low pressure settles depending on control current for A/C Compressor Regulator Valve -N280- and control characteristic of expansion valve within compressor output range in tolerance range. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
Under unfavorable conditions (very high ambient temperatures, or high humidity) the output of the A/C compressor may not always be sufficient to attain the specified pressure values within the specified time (depending on the engine speed it can take longer until the specified low pressure can be reached).
If the A/C compressor load is greater than 90%, the pressure on the low pressure side can be greater than the specified tolerance range. The A/C compressor load is no longer sufficient to reduce the pressure on the low pressure side to the value of approximately 2 bar (29 psi) under predominant ambient conditions (ambient temperature, humidity, A/C compressor settings, engine speed etc.).
The specified operating current for the A/C Compressor Regulator Valve -N280- must be greater than 0.3 A in order to ensure reliable A/C Compressor Regulator Valve -N280- actuation. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
In "maximum cooling output" setting, control current for A/C Compressor Regulator Valve -N280- is regulated to approximately 0.65 A (up to 0.85 A). The measured value is vehicle-specific and is displayed in the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
At absolute pressure, 0 bar (0 psi) corresponds to absolute vacuum. Normal ambient pressure corresponds to 1 bar (14.5 psi) absolute pressure. 0 bar (0 psi) pressure corresponds to an absolute pressure of 1 bar (14.5 psi) on most pressure gauges (indicated for example by -1 bar (-14.5 psi) below 0). Depending on the version of the corresponding control module the pressure is displayed as a measured value on the basis of the absolute pressure and relative pressure (difference between the display 1 bar (14.5 psi)). Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system. Refer to REPAIR INFORMATION .
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 as well as the specified operating current for the A/C Compressor Regulator Valve -N280- is displayed for example as the measured value of the display control head of the Climatronic Control Module -J255-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
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| Possible Deviation From Specified Value During The Pressure Test |
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| Possible causes for the deviation from specified value and their solutions |
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| Final Procedures |
| -- Charge the refrigerant circuit. Refer to WORKING WITH A/C SERVICE STATION .-- Repeat the test. Refer to PRESSURES, CHECKING . |
Pay attention that the A/C compressor (the shaft of the A/C compressor) under these concern is actually driven by the belt pulley/the drive unit. Refer to A/C COMPRESSOR and REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
In no malfunction is determined for this concern, clean the refrigerant circuit (flush with refrigerant R1234yf). Refer to REFRIGERANT CIRCUIT .
Check the measured values of the Evaporator Vent Temperature Sensor -G263- and the activation of the A/C Compressor Regulator Valve -N280-. If the measured value of the Evaporator Vent Temperature Sensor -G263- malfunctions the evaporator can ice over or the cooling output is not reached. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
If the A/C system function is not OK after repeating the test, for example after replacing expansion valve, clean the refrigerant circuit by flushing using the refrigerant R1234yf. Refer to REFRIGERANT CIRCUIT . Replace the A/C compressor and dryer cartridge (or reservoir/receiver/dryer). Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
With this malfunction, evaporator may ice up although the quantity of refrigerant in circuit is OK.
If the expansion valve is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve -N280- is actuated to maximum output and the low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system. As however refrigerant cannot flow via the expansion valve, the cooling output is not attained and high pressure may also not increase or only increase slightly due to the absence of energy conversion.
| Possible Deviation From Specified Value During The Pressure Test |
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| Possible causes for the deviation from specified value and their solutions |
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| Final Procedures |
| -- Charge the refrigerant circuit. Refer to WORKING WITH A/C SERVICE STATION .-- Repeat the test. Refer to PRESSURES, CHECKING . |
Check the measured values of the Evaporator Vent Temperature Sensor -G263- and the activation of the A/C Compressor Regulator Valve -N280-. If the measured value of the Evaporator Vent Temperature Sensor -G263- malfunctions the evaporator can ice over or the cooling output is not reached. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
If the A/C system function is not OK after repeating the test, for example after replacing expansion valve, clean the refrigerant circuit by flushing using the refrigerant R1234yf. Refer to REFRIGERANT CIRCUIT . Then replace the A/C compressor and reservoir/receiver/dryer (or dryer cartridge). Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
| Possible Deviation From Specified Value During The Pressure Test |
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| Possible causes for the deviation from specified value and their solutions |
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| Final Procedures |
| -- Charge the refrigerant circuit. Refer to WORKING WITH A/C SERVICE STATION .-- Repeat the test. Refer to PRESSURES, CHECKING . |
Make sure that the A/C compressor (the A/C compressor shaft) is actually being driven by the belt pulley/drive unit for this complaint (pay attention to the overload protection). Refer to A/C COMPRESSOR .
For some engines, A/C compressor are being introduced that, in addition to the A/C Compressor Regulator Valve -N280-, an A/C Clutch -N25- is being attached to the belt pulley. Make sure that the A/C Clutch -N25- is actually being actuated and the A/C compressor (A/C compressor shaft) is being driven by the belt pulley. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
In no malfunction is determined for this concern, clean the refrigerant circuit (flush with refrigerant R1234yf). Refer to REFRIGERANT CIRCUIT .
Check the measured values of the Evaporator Vent Temperature Sensor -G263- and the activation of the A/C Compressor Regulator Valve -N280-. If the measured value of the Evaporator Vent Temperature Sensor -G263- malfunctions the evaporator can ice over or the cooling output is not reached. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
If the A/C system function is not OK after repeating the test, for example after replacing expansion valve, clean the refrigerant circuit by flushing using the refrigerant R1234yf. Refer to REFRIGERANT CIRCUIT . Then replace the A/C compressor and reservoir/receiver/dryer (or dryer cartridge). Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
If the expansion valve is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve -N280- is actuated to maximum output and the low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system. As however refrigerant cannot flow via the expansion valve, the cooling output is not attained and high pressure may also not increase or only increase slightly due to the absence of energy conversion.
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| Possible causes for the deviation from specified value and their solutions |
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| Final Procedures |
| -- Charge the refrigerant circuit. Refer to WORKING WITH A/C SERVICE STATION .-- Repeat the test. Refer to PRESSURES, CHECKING . |
With this malfunction, evaporator may ice up although the quantity of refrigerant in circuit is OK.
If the expansion valve is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve -N280- is actuated to maximum output and low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). As the refrigerant cannot flow via the expansion valve, if the cooling output is not attained, high pressure may also not increase or only increase slightly due to the absence of energy. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" Function for the A/C system. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
If there is too much refrigerant oil in the circuit, the A/C compressor must be emptied and the desiccant bag (the dryer cartridge) or the receiver/receiver/dryer must be replaced. After cleaning (flushing with refrigerant R1234yf) fill the refrigerant circuit with the correct quantity of refrigerant oil. Refer to REFRIGERANT CIRCUIT and TECHNICAL DATA . and REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT
If the specified value when repeating the check is still not reached and on the refrigerant circuit no malfunction can be determined, clean the refrigerant circuit (flush with refrigerant R1234yf). Refer to REFRIGERANT CIRCUIT .
| Possible Deviation From Specified Value During The Pressure Test |
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| Possible causes for the deviation from specified value and their solutions |
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| Final Procedures |
| -- Charge the refrigerant circuit. Refer to WORKING WITH A/C SERVICE STATION .-- Repeat the test. Refer to PRESSURES, CHECKING . |
If there is too much refrigerant oil in the circuit, the A/C compressor must be emptied and the desiccant bag (the dryer cartridge) or the receiver/receiver/dryer must be replaced. After cleaning (flushing with refrigerant R1234yf) fill the refrigerant circuit with the correct quantity of refrigerant oil. Refer to REFRIGERANT CIRCUIT or REPAIR INFORMATION /TECHNICAL DATA . and REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
With this malfunction, evaporator may ice up although the quantity of refrigerant in circuit is OK.
A malfunction on the Evaporator Vent Temperature Sensor -G263- can also cause icing-up of refrigerant circuit. For this concern also pay attention to the measured value of the Evaporator Vent Temperature Sensor -G263-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system. Refer to COMPONENT LOCATION OVERVIEW - A/C SYSTEM .
| Possible Deviation From Specified Value During The Pressure Test |
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| Possible causes for the deviation from specified value and their solutions |
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| Final Procedures |
| -- Charge the refrigerant circuit. Refer to WORKING WITH A/C SERVICE STATION .-- Repeat the test. Refer to PRESSURES, CHECKING . |
With this malfunction, evaporator may ice up although the quantity of refrigerant in circuit is OK.
A malfunction on the Evaporator Vent Temperature Sensor -G263- can also cause icing-up of refrigerant circuit. For this concern also pay attention to the Evaporator Vent Temperature Sensor -G263- measured value.
If there is moisture in the circuit, discharge the A/C compressor and replace the desiccant bag/dryer cartridge (or receiver/receiver/dryer). After cleaning (flushing with refrigerant R1234yf) ill the refrigerant circuit with the correct quantity of refrigerant oil. Refer to TECHNICAL DATA . and REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
| Possible Deviation From Specified Value During The Pressure Test |
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| Possible causes for the deviation from specified value and their solutions |
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| Final Procedures |
| -- Charge the refrigerant circuit. Refer to WORKING WITH A/C SERVICE STATION .-- Repeat the test. Refer to PRESSURES, CHECKING . |
For the malfunction "high pressure normal, low pressure too low" With this malfunction, evaporator may ice up, although quantity of refrigerant in circuit is OK.
If there is a malfunction on a present shut-off valve (the shut-off valve does not open) it is not necessary to clean the refrigerant circuit (flush with refrigerant R1234yf. Refer to REFRIGERANT CIRCUIT ). For this malfunction it is sufficient to check the activation of the shut-off valve, if this is OK replace the shut-off valve.
If the problem is with the A/C Compressor Regulator Valve -N280- (regulating valve is not actuated but compressor operates nevertheless), refrigerant circuit needs to be cleaned (flush with refrigerant R1234yf. Refer to REFRIGERANT CIRCUIT ). In this case, it is sufficient to replace the A/C compressor (observe quantity of refrigerant oil in A/C compressor).
If the expansion valve is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve -N280- is actuated to maximum output and low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). As however refrigerant cannot flow via the expansion valve, the cooling output is not always attained and high pressure may also not increase or only increase slightly due to the absence of energy conversion. For these malfunctions it is not necessary to clean the refrigerant circuit (flush with refrigerant R1234yf. Refer to REFRIGERANT CIRCUIT ) it is sufficient to replace the expansion valve.
Check measured values of the Evaporator Vent Temperature Sensor -G263- and the actuation of the A/C Compressor Regulator Valve -N280-. If the measured value of the Evaporator Vent Temperature Sensor -G263- malfunctions the evaporator can ice over or the cooling output is not reached. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
| Possible Deviation From Specified Value During The Pressure Test |
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| Possible causes for the deviation from specified value and their solutions |
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| Final Procedures |
| -- Charge the refrigerant circuit. Refer to WORKING WITH A/C SERVICE STATION .-- Repeat the test. Refer to PRESSURES, CHECKING . |
This fault may also be caused by too much refrigerant oil in the refrigerant circuit. Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil. If there is too much refrigerant oil in the refrigerant circuit, clean the refrigerant circuit (flush with refrigerant R1234yf). Refer to REFRIGERANT CIRCUIT .
If the expansion valve (or a present shut-off valve) is faulty (constantly closed or does not open far enough), the A/C Compressor Regulator Valve -N280- is actuated to maximum output and low pressure drops to value in graph or below (the A/C compressor draws off refrigerant from low-pressure side). As the refrigerant cannot flow via the expansion valve, if the cooling output is not attained, high pressure may also not increase or only increase slightly due to the absence of energy. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" Function for the A/C system. Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT .
| Possible Deviation From Specified Value During The Pressure Test |
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| Possible causes for the deviation from specified value and their solutions |
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| Final Procedures |
| -- Charge the refrigerant circuit. Refer to WORKING WITH A/C SERVICE STATION .-- Repeat the test. Refer to PRESSURES, CHECKING . |
Check the measured values of the Evaporator Vent Temperature Sensor -G263- and the activation of the A/C Compressor Regulator Valve -N280-. If measured value of Evaporator Vent Temperature Sensor -G263- is incorrect, evaporator may ice up or cooling output is not attained use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function for the A/C system. Refer to REFRIGERANT CIRCUIT .
Overfilling with refrigerant oil can occur if, for example, the compressor has been replaced without adjusting the quantity of refrigerant oil.
If expansion valve is malfunctioning (permanently open), evaporator temperature is no longer regulated such that only refrigerant in gaseous state exits from the evaporator. Under certain usage conditions, liquid droplets may then be drawn in by the compressor and cause noise (liquid cannot be compressed).
If too much refrigerant oil is located in the circuit, the A/C compressor must be discharges and if equipped replace the receiver/receiver/dryer (or dryer cartridge). Refer to REFRIGERANT CIRCUIT or REFRIGERANT CIRCUIT . After cleaning the refrigerant circuit (flushing with refrigerant R1234yf. Refer to REFRIGERANT CIRCUIT ) fill it with the correct quantity of refrigerant oil in the circuit. Refer to TECHNICAL DATA .