Cooling Output, Checking
Cooling Output, Checking
Special tools, testers and auxiliary items required
• Vehicle diagnosis, testing and information system (VAS5051B) (or Vehicle Diagnosis and Service System (VAS 5052) ).
• A standard thermometer (for temperature measurements, if necessary a thermometer with 2 measuring probes for simultaneous measurement e.g. for temperature on the right and left).
Test requirements are met, refer to=> [ Test Requirements ] Test Requirements.
- Measure the ambient temperature (it must higher than 15 °C).
- Close doors, hood, windows and sun roof.
- Open all instrument panel vents.
- Switch ignition on.
- Switch off the A/C compressor via the -button (indicator lamp in -button does not light up).
- Start the engine.
- Initiate a Guided Fault Finding on the A/C system using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
- Select "Guided Fault Finding" and read the following values ( A/C compressor regulator valve (N280) activation and high pressure sensor (G65) using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• The A/C compressor activation is switched off.
• The pressure in the refrigerant circuit is same as the measured outside temperature or greater than the value in the chart.
• In terms of absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure equals approximately 1 bar absolute pressure. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of one bar (can be seen from -1 mark below 0).
• Pressure in refrigerant circuit is governed by ambient temperature. On account of heat given off by components (e.g. radiator), pressure displayed with warm engine will be slightly higher than that given for the respective ambient temperature.
• Only integer values are displayed for the pressure in refrigerant circuit in the measuring value block of A/C control module (J301) , if the value measured lies between two values the display switches back and forth.
If the displayed pressure in the refrigerant circuit is lower than in the table
• Check signal of High Pressure Sensor (G65). Refer to=> [ High Pressure Sensor (G65), Checking Pressure Signal ] Testing and Inspection.
• If no malfunction can be detected at High Pressure Sensor (G65) , there is insufficient refrigerant in the circuit, bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel.
If pressure in refrigerant circuit is OK (the same or greater than specified in the table)
- Switch on the A/C compressor, to do so press the AC button on A/C control module (J301) (indicator lamp in AC button comes on)
- Set the lowest possible temperature (turn the temperature rotary switch all the way to "cold").
- Set the air flow direction to "instrument panel vents" via the air distribution rotary switch.
- Set speed 4 on fresh air blower rotary switch.
- Switch A/C system to recirculating air mode by pressing "recirculating air mode" button on (indicator lamp in "recirculating air button" comes on).
- Select "Guided Fault Finding"and read the following values using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• The current, calculated by the A/C control module (J301) , which flows via the A/C Compressor Regulator Valve (N280) is greater than 0.3 Amps (the compressor is switched on)
• The displayed pressure increases above the value when the compressor is switched off.
• If the pressure displayed does not change and yet the A/C compressor activation is OK, make sure the calculated current is actually flowing via the A/C compressor regulator valve (N280) and that the A/C compressor is actually being driven. There is a fault in the refrigerant circuit if the current is flowing via the A/C compressor regulator valve and the A/C compressor is being driven. Bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel.
• A/C Compressor Regulator Valve (N280) is activated by A/C Control Module (J301) so that temperature of air downstream of evaporator reaches the specified value (approximately 2 to 5 °C):
• A value greater than 0.55 A is displayed after vehicle start, depending on measured temperature, engine speed and vehicle voltage for activation of A/C Compressor Regulator Valve. As soon as the temperature measured by the evaporator vent temperature sensor (G263) nears the target value, the activation, and thus the compressor output, is reduced.
• Under certain operating conditions, moisture in the refrigerant circuit can lead to ice build-up on the A/C compressor regulator valve (and on the expansion valve). A/C compressor control is reduced by this ice build-up, evaporator is cooled too intensely and freezes. The ice on the evaporator may cause various customer concerns. Refer to => [ Ice Formation on Evaporator, Localizing Malfunction ] Ice Formation on Evaporator, Localizing Malfunction.
• If no voltage or voltage that is too low is shown in the measured values block for the A/C compressor regulator valve activation, check the A/C compressor regulator valve activation. Refer to=> [ A/C Compressor Regulator Valve (N280), Checking Switch-On Signal ] A/C Compressor Regulator Valve (N280), Checking Switch-On Signal.
- Press button for recirculating air mode on A/C Control Module (J301) (indicator lamp for "recirculating air mode" in button lights up).
- Set engine speed of 2000 rpm (start of time measurement).
- Select "read measured values block" on the Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
- Compare the displayed measured value evaporator vent temperature sensor (G263) ) to the values in the diagram.
A Measured air temperature of Evaporator Vent Temperature Sensor
B Ambient temperature
C Permissible tolerance range
Depending on the ambient temperature, the measured air temperature should be after 5 minutes within the shown tolerance range.
• If the required values have not been reached, measure temperature of the air flowing out of instrument panel vents using a thermometer. Compare this value with the displayed measured value of Evaporator Vent Temperature Sensor (G263). If both measure values deviate only slightly from one another, perform malfunction identification when specified value is not reached. Refer to=> [ Determining Malfunction if Specified Values Are Not Obtained ] Determining Malfunction if Specified Values Are Not Obtained. If the measured value from the evaporator vent temperature sensor is larger than your measured value, then make sure the evaporator vent temperature sensor is installed correctly and perform an electrical test on the sensor using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• The function of the air conditioning is recognizable, e.g. the refrigerant pipe on the low pressure side (thick line) cools off.
If the measured value for the evaporator vent temperature sensor (and therefore the system output) is OK:
- Measure temperature of the air flowing out of left and right instrument panel vents using a thermometer.
- Compare your measured values ( Left Vent Temperature Sensor (G150) , Right Vent Temperature Sensor (G151) and Evaporator Vent Temperature Sensor (G263) ). The measured values may not be smaller and after 5 minutes be greater than maximum 3 °C, than the value of the Evaporator Vent Temperature Sensor.
• If the measured value are smaller, make sure the Evaporator Vent Temperature Sensor is installed correctly and check the electrical connections for contact resistance; replace the sensor if it is defective. Check using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• Check the activation and function of the temperature doors if the required values on or both sides are not reached. Perform Guided Fault Finding if the temperature increases after the evaporator. Refer to => [ Temperature Increase Downstream from Evaporator, Determining Malfunction ] Temperature Increase Downstream From Evaporator, Determining Malfunction and Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.
• Problems relating to differences between temperature of air emitted by left and right vents with identical setting in air conditioner regulated mode may have the following causes: One of the temperature doors in air distribution housing does not close completely or does not reach its end position. Refer to => [ Air Guide In Evaporator Housing ] Air Guide In Evaporator Housing and Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function. There is air in the heater cores (fluctuating flow through heater core and heat is not distributed uniformly). Refer to=> [ Heating Performance Of A/C System, Checking ] Heating Performance Of A/C System, Checking or a foam seal was loosened during installation of the heater core and air may bypass the heater core.