A/C Unit, Checking Cooling Output
A/C Unit, Checking Cooling Output
=> [ Checking ]
=> [ Determining Malfunction if Specified Values Are Not Obtained ]
=> [ Temperature Increase Downstream from Evaporator, Determining Malfunction ]
Special tools, testers and auxiliary items required
• Vehicle Diagnosis, Testing and Information System ( VAS 5051A) e.g. with the diagnostic cable (VAS 5051/5A) and the K-wire adapter (VAS 6017B) (or the K-wire adapter (VAS 6017A)
• Mini-tester (V.A.G 1362) (for temperature measurement) or a commercially available thermometer
Test Prerequisites
• Ambient temperature greater than 15 °C
• Clean radiator and condenser (clean if necessary)
• The ribbed belt for the compressor drive is OK and correctly tensioned and the belt pulley actually drives the compressor (not in vehicles with an 8 cylinder engine).
• The compressor drive unit (connection between the compressor and engine) is installed correctly (only in vehicles with an 8 cylinder engine).
• All air ducts, covers and seals OK and properly fitted
• Air flow through dust and pollen filter not obstructed by dirt.
• Vehicle not exposed to sunlight
• Engine is warm
• The DTC memory was queried. Refer to => [ DTC Memory, Interrogating ] DTC Memory, Interrogating, all displayed faults were eliminated and the DTC memory was erased. Refer to => [ Erasing DTC Memory, Ending Output ] Erasing DTC Memory, Ending Output.
• The coding was checked and corrected if necessary. Refer to => [ A/C Control Head Climatronic Control Module, Coding ] A/C Control Head Climatronic Control Module, Coding and read the measured value block.
• The basic setting was performed. Refer to => [ Basic Setting ] Basic Setting.
• All instrument panel vents open
• Hood closed
• Settings on A/C control head Climatronic Control Module (J255):
- Operating mode "Auto".
- Temperature selection "Low" (for the driver and passenger side).
- Compressor on (indicator light in the ECON button does not illuminate)
• Functions with the engine running (and the A/C system switched on):
- The coolant fan(s) (V7) is/are running or is/are switched on as soon as a certain pressure is exceeded in the refrigerant circuit (the speed depends on the pressure in the refrigerant circuit and the engine temperature).
• Depending on the version of the Climatronic control module (J255) A/C control head, the coolant fan is switched on immediately in the 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.
- Fresh Air Blower (V2) runs at maximum speed.
- The A/C system switches to recirculation mode (approximately 1 minute after starting the vehicle, the fresh air/back pressure flaps will be closed and the recirculation flap will open. The fresh air blower (V2) extracts air from the footwell on the passenger side).
• If one of the test conditions is not met, query the DTC memory. Refer to => [ DTC Memory, Interrogating ] DTC Memory, Interrogating and conduct the output diagnostic test mode => [ Final Control Diagnosis ] Final Control Diagnosis.
Checking
- Measure ambient temperature (must be greater than 15 °C).
- Close doors, hood, windows and sun roof.
- Open all instrument panel vents.
- Switch ignition on.
- Set the "Econ" operating mode on the Climatronic control module (J255) A/C control head (indicator light in the ECON button lights up).
- Start the engine.
- Start the A/C system on board diagnostic. Refer to => [ VAS 5051A, Connecting and Selecting Functions ] VAS 5051A, Connecting and Selecting Functions
- Select display group "001". Refer to => [ Display Group 001 ] Measured Value Blocks for Display Groups 001 Through 010 in the "read measured value block" function.
- Check display in display zones:
- Display field "2" shows 0% (compressor is switched off)
- Display field "4" shows that the pressure in the refrigerant circuit measured at ambient temperature is the same or greater as the table value.
• At absolute pressure, "0 bar" corresponds to an absolute vacuum. The normal ambient pressure equals approximately "1 bar" absolute pressure. "0 bar" corresponds to an absolute pressure of one bar on most pressure gauges (indicated by "-1" 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.
• If the displayed pressure is less than the pressure specified in the table, check the measured value of the high pressure sensor (G65) "Read measured value block" and => [ Test Step 5 ] Climatronic Control Module A/C Control Head Electrical Test "Electrical testing test step 5". If no fault can be detected at the high pressure sensor, there is insufficient refrigerant in the circuit. Bring the vehicle to an A/C system service point workshop.
If pressure in refrigerant circuit is OK:
- Switch the compressor on and select the "Auto" operating mode on the Climatronic control module (J255) A/C control head (the indicator light in the ECON button does not illuminate).
- Set temperature preselect for driver's and front passenger's side to "Low" on A/C control head Climatronic Control Module (J255).
- Set the direction of air flow to the "instrument panel vents " on the Climatronic control module (J255) A/C control head.
- Select display group "001" => [ Display Group 001 ] Measured Value Blocks for Display Groups 001 Through 010 in the "read measured value block" function.
- Check display in display zones:
- Display field "2" shows a duty cycle greater than 30% (A/C Compressor Regulator Valve (N280) is activated, compressor is switched on)
- Display field "1" shows a current greater than 0.3 A (current flows via A/C Compressor Regulator Valve (N280 ), compressor is switched on)
- The displayed pressure in display field "4" rises above the value with the compressor switched off.
• The A/C compressor regulator valve (N280) is activated by the Climatronic control module (J255) A/C control head so that the temperature of the air downstream from the evaporator reaches the specified value (approximately 2 to 5°C): After starting vehicle, value greater than 75 % (0,55 A) is displayed depending on measured temperature, engine speed and electrical system voltage. As soon as the temperature measured by evaporator vent temperature sensor (G263) nears the specified value, the activation, and thus the compressor output, is reduced.
• Under certain operating conditions, residual moisture in refrigerant circuit can lead to an ice build-up at compressor regulator valve. This impedes compressor regulation. Evaporator is excessively cooled and ices up. The freeze-up of the evaporator can be the cause for the following customer complaints:
• - After a long drive, A/C system repeatedly or sporadically fails (no cooling or heating performance), after switching off vehicle and after a short time, A/C function is OK again.
• - After a long drive, windows fog up from inside, windows are also not cleared by then pressing the "Defrost" button, after switching off vehicle and after a short time, A/C function is OK again.
• Corrective action:
• - Check the measured value of the evaporator vent temperature sensor (G263) "Read the measured value block" display group "010".
• If measured value of sensor is too high under operating conditions reported by customer (even though A/C system is operating without difficulty at greater than e.g. 10 °C), check Evaporator Vent Temperature Sensor (G263) (incorrect measured value may cause evaporator to ice up).
• - If the measured value of the sensor is too low under the operating conditions reported by the customer (at an ambient temperature above 0°C, colder than 0°C for a long period of time) even though the A/C compressor regulator valve (N280) is not currently activated, bring the vehicle to an A/C system support point workshop.
• - Check the refrigerant line from the evaporator to the accumulator (thick tube, low pressure side) with the engine running. If this line is thickly iced-up when a problem occurs (a very thin layer of ice is permitted), this indicates that the temperature in the evaporator is too low.
• - Bring the determined deficiency to the attention of the A/C system support point workshop, the necessary work can only be performed there (draining refrigerant circuit, replacing reservoir and then evacuating refrigerant circuit for minimum of 3 hours).
• - If no or very little current is displayed in display field " 1", check the activation of the A/C compressor regulator valve (N280) => [ Test Step 5 ] Climatronic Control Module A/C Control Head Electrical Test " Electrical testing test step 6".
• - If the pressure displayed in display group "4" does not change and compressor activation is OK (display fields "1" and " 2"), there is a fault in the refrigerant circuit. Take the vehicle to an A/C system service point workshop.
- Press the button for the recirculation flap (the symbol for " recirculation mode" in the button illuminates).
- Set engine speed of 2000 rpm (start of time measurement).
- Select display group "010" => [ Display Group 010 ] Measured Value Blocks for Display Groups 001 Through 010 in the "read measured value block" function.
- Compare the displayed measured value (of the evaporator vent temperature sensor (G263)) in display field " 1" with values in the diagram.
A Measured air temperature of Evaporator Vent Temperature Sensor (G263)
B Ambient temperature
C Permissible tolerance range
Depending on ambient temperature, air temperature measured must be within stated tolerance range after 5 minutes.
• If the requested values are not obtained, check the measured value of the evaporator vent temperature sensor (G263) and compare the measured values displayed in display group "010", display fields "1" and "009" with display fields " 3" and "4":
• - If the measured value in display field "3" or " 4" deviates only slightly from the measured value of display group " 010". Perform "Identifying malfunctions if specified values are not obtained". Refer to => [ Determining Malfunction if Specified Values Are Not Obtained ].
• - If the measured value of the evaporator vent temperature sensor (G263) is greater than the measured value of the left vent temperature sensor (G150) and the right vent temperature sensor (G151), check the evaporator vent temperature sensor (G263) for proper installation and perform an electrical test for this sensor. Refer to => [ Test Step 2 ] Climatronic Control Module A/C Control Head Electrical Test "Electrical testing test step 2".
• The function of the A/C system is recognizable, e.g. in that the refrigerant pipe on the "low pressure side" (thick line) cools off.
If the measured value of the evaporator vent temperature sensor (G263) (and therefore the cooling output of the A/C system) is OK.
- Compare the displayed measured value (of evaporator vent temperature sensor (G263)) in display field "1" of display group "010" with the measured values of display group " 009" display fields "3" and "4" ( left vent temperature sensor (G150) and right vent temperature sensor (G151)).
After a maximum of 5 minutes, the measured values in display group " 009" display fields "3" and "4" ( left vent temperature sensor (G150) and right vent temperature sensor (G151)) must be 3°C greater than the value in display field "1" of display group " 010" (of the evaporator vent temperature sensor ( G263)).
• If the required values are not obtained, compare displayed measuring values in display group "009" display fields "3" and " 4" with each other:
• - If the measured value in display field "3" or " 4" is OK, check the temperature flap control motor on the side where the measured value is not OK (left temperature flap motor ( V158) or right temperature flap motor (V159)) and conduct the electrical test for the left vent temperature sensor (G150) and right vent temperature sensor (G151) via => [ Test Step 2 ] Climatronic Control Module A/C Control Head Electrical Test " Electrical testing test step 2".
• - If the measured value in display field "3" or " 4" of display group "009" is less than that in display field "1" display group "010". Check the evaporator vent temperature sensor (G263), left vent temperature sensor (G150), and right vent temperature sensor (G151) for correct installation and check their electrical connections for contact resistance, replace the malfunctioning sensor if necessary.
• - If no fault can be detected at the left vent temperature sensor (G150) and the right vent temperature sensor (G151) as well as at the left temperature flap motor (V158) and the right temperature flap motor (V159), perform "Identifying malfunctions in the case of a temperature increase downstream from the evaporator". Refer to => [ Temperature Increase Downstream from Evaporator, Determining Malfunction ].
• The temperature of air flowing out of the "center" instrument panel vents can also be measured e.g. with the mini-tester (V.A.G 1362) (or a commercially available thermometer).
• In display group "009" the measured value of the left footwell vent temperature sensor (G261) and the right footwell vent temperature sensor (G262) is displayed in display fields "1" and "2". Since the air flow is only directed to the instrument panel vents in the "auto" operating mode, these two sensor show an inexact value in this setting. By pressing the "air down" button, these sensors can also be included in the test.
Determining Malfunction if Specified Values Are Not Obtained
* Prior to bringing the vehicle to an A/C system support point workshop, check that the compressor is actually being driven. In vehicles with an 8 cylinder engine, the drive shaft can disconnect from the drive unit, for example => [ Compressor Drive Unit ] Compressor Drive Unit
Continuation of test (the pressure in the refrigerant circuit increases)
• Pressure in refrigerant circuit is governed by various factors of influence. However, at an ambient temperature between 20 to 25 °C the pressure should not exceed more than 20 bar. Due to the necessary high coolant output, pressures up to 31 bar may occur under extreme operating conditions (e.g. in southern countries with a high ambient temperatures, "stop and go" traffic, and high relative humidity).
• The pressure in the refrigerant circuit typically does not increase above 16 bar at ambient temperatures less than 25°C (the coolant fan(s) (V7) runs/run and cools/cool the condenser).
• The Climatronic control module (J255) A/C control head calculates the pressure in the refrigerant circuit via the duty cycle (read the measured value block, display group "001", display field "3").
• At a duty cycle less than 12,5% (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 12,5% (corresponds to 1.8 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 27 bar.
• - As soon as coolant temperature exceeds 115° C (full shutdown at 118° C).
• If the pressure in the refrigerant circuit was greater than 32 bar (duty cycle greater than 87,5%) the compressor is switched on again by A/C control head Climatronic Control Module (J255), if pressure drops below 29 bar (duty cycle is less than 84%).
• Additional information regarding the pressure in the refrigerant circuit is available in "Read the measured value block", display group " 001"
Temperature Increase Downstream from Evaporator, Determining Malfunction
