Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Display And Control Head Location
The Climatronic Control Module -J255-
- From 08/2007, the "Convenience" A/C system with an air distribution housing with optimized air distribution will be introduced (distinguishing characteristic between versions "1" and "2". Refer to NOTES ON FRONT HEATER AND A/C UNIT and the Parts Information).
- The Coolant Recirculation Pump -V50- (Water Pump -V36-) activation differs depending on the date of manufacture.
The Coolant Recirculation Pump -V50- (Water Pump -V36-) version and activation differ depending on the vehicle version and production period. From MY 2012 as a running change, the pumps installed from the start of production, which were activated via a 500 Hertz signal (500 pulses per second), are being replaced by pumps that are activated by a variable (100 to 500 Hertz) signal depending on the engine. Pumps, controlled by a variable signal, also have a diagnostic function and are controlled by the engine control module. Check for the correct allocation using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. Refer to Wiring Diagram and to the Parts Information.
-- On vehicles with the A/C unit version "2", only the Climatronic Control Module -J255- A/C display and control heads with the "Convenience" version with part number "8T1 820 043" beginning with the index "Q" are or will be installed.
-- If on vehicles with the A/C unit version "1", a Climatronic Control Module -J255- A/C display and control head with the "Convenience" version, with part number "8T1 820 043" beginning with the letter "Q" is installed, the adaptation is changed accordingly using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
There is a label -A- on the outside of the A/C unit with a part number -B- that tells which version is installed. Refer to the Parts Information.
The part number -B- on the label -A- can be read, for example, when the CD changer is removed (depending on the vehicle equipment level). Refer to CD CHANGER, REMOVING AND INSTALLING .
-- The Climatronic Control Module -J255- A/C display and control heads for the "Convenience" version with the part number "8T1 820 043" up to letter "L" may not be installed on the A/C unit version "2".
On the "Basis" A/C system, the A/C unit and the air distribution housing were not changed.
- On the Audi A5 coupe and Audi A4 from MY 2009, the Climatronic Control Module -J255- display and control heads with the part number 8T1 820 043 starting with the index "T" are installed (on the Audi Q5 this was already installed since the start of production). Refer to the Parts Information.
-- On vehicles with these display and control heads, and depending on the coding and adaptation, for example the display on the screen for the "MMI" (Multi Media Interface), when using the buttons and knobs, the display and control head no longer switches to "A/C system". The selected functions for the A/C system appear in the display sequentially using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function, the "Infotainment/MMI" Operating Instructions and the Owner's Manual.
-- Pay attention to the correct allocation, coding and adaptation of the Climatronic Control Module -J255- display and control head to the Front Information Display Control Head Control Module -J523- to the Information Electronics Control Module 1 -J794-. Refer to the Parts Information and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. If the allocation, coding or adaptation are incorrect, the A/C system functions cannot be displayed or selected in the MMI.
The Climatronic Control Module -J255- display and control heads with the part number 8T1 820 043 up to index "S" are installed on vehicles with a Front Information Display Control Head Control Module -J523-.
The Climatronic Control Module -J255- display and control heads with the part number 8T1 820 043 from index "T" may be installed on vehicles with an Information Electronics Control Module 1 -J794-. In order to be able to select and display the different functions, the coding and adaptation must be correct for the vehicle equipment level.
- From MY 2010, this vehicle has a Start/Stop System for specific engines as optional equipment.
- As a running change in MY 2010, gasoline engines that can run on bioethanol (Flex Fuel Vehicles) were introduced
On vehicles with Start/Stop system, the Climatronic Control Module -J255- display and control head prevents the Stop function depending on the setting. If, for example, "defrost" is selected, the stop function is not possible or will be interrupted and the engine will start. The same applies in the case of heating and cooling. The difference between the selected and actual temperature exceeds a certain value using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
If the vehicle has a Start/Stop System, then only the Climatronic Control Module -J255- display and control head with the part number 8T1 820 043 starting with index "AG" or with part number 8K_ 820 043 may be installed. Refer to Parts Information and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
The activation of an installed Coolant Recirculation Pump -V50- (Water Pump -V36-) differs depending on the date of manufacture and on the vehicle version. Make sure to use the correct version of the Climatronic Control Module -J255-. Also note the adaptation for the Coolant Recirculation Pump -V50- (Water Pump -V36-) activation on a Climatronic Control Module -J255- with the part number 8T1 820 043 starting with index "AG". Refer to COOLANT RECIRCULATION PUMP -V50- (WATER PUMP -V36-), LOCATION, ACTIVATION AND FUNCTION, VEHICLES WITH 6-CYLINDER GASOLINE ENGINE and to using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
The Coolant Recirculation Pump -V50- (Water Pump -V36-) version and activation differ depending on the vehicle version and production period. From MY 2012 as a running change, the pumps installed from the start of production, which were activated via a 500 Hertz signal (500 pulses per second), are being replaced by pumps that are activated by a variable (100 to 500 Hertz) signal depending on the engine. Pumps that are activated by a variable signal are also equipped with a diagnostic function and are activated mostly via the respective engine control module. Therefore, ensure the correct allocation (only the allocated pump can be activated) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. Refer to Wiring Diagram and to the Parts Information.
As a running change in MY 2010, gasoline engines that can run on bioethanol (Flex Fuel vehicles) were introduced, which currently have an Auxiliary Heater Heating Element -Z35-. Refer to AUXILIARY HEATER HEATING ELEMENT -Z35-, CHECKING . For vehicles with a gasoline engine, the electric auxiliary heater (the Auxiliary Heater Heating Element -Z35-) is activated by the Climatronic Control Module -J255- display and control head via the local Data Bus (activated via the same outlet and also via the Fresh Air Blower Control Module -J126-) on the Auxiliary Air Heater Control Module -J604-. Refer to Wiring Diagram.
If the vehicle has a gasoline engine that can run on bioethanol, then only the Climatronic Control Module -J255- display and control head with the part number 8T1 820 043 starting with index "AG" or with part number 8K_ 820 043 may be installed. Refer to Parts Information and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- Vehicles With A High Voltage System (Hybrid Vehicles)
Only the Climatronic Control Module -J255- display and control head with the part number 8R1 820 043 may be installed on vehicles with a high voltage system (only for vehicles until the version changeover) (from MY 2012 see below). Refer to the Parts Information and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
Climatronic Control Module -J255- display and control head with the part number 8R1 820 043 may only be installed on vehicles with a high voltage system up to the vehicle version changeover (from MY 2012 see below). After the vehicle version changeover, the Climatronic Control Module -J255- display and control heads with the part number 8K_ 820 043 are being installed in vehicles with a high voltage system. Pay attention to the part number index and coding. Refer to the Parts Information and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
For vehicles built after the version changeover, only one Climatronic Control Module -J255- may be installed that are available, so that the various functions necessary for vehicles with a high voltage system can be performed by the Climatronic Control Module -J255- display and control head. A Climatronic Control Module -J255- with part number 8K_ 820 043 and index "K or AA" through index "P or AE" does not have the necessary functions needed by high voltage vehicles, for example. These functions are integrated on a Climatronic Control Module -J255- with part number 8K_ 820 043 from index "Q or AF". Instead of a Climatronic Control Module -J255- with part number 8Kx 820 043 and index "Q", the version with index "AF" can be installed, for example (the existing function for activating the A/C Clutch -N25- is not used). Refer to the Parts Information. The coding of the Climatronic Control Module -J255- turns off or activates the necessary functions for the respective vehicle using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- From MY 2012, as a running change (depending on the model and version), a revised Climatronic Control Module -J255- is being installed. Ensure the correct allocation. Refer to the Parts Information.
From MY 2012, the changeover was made on the Audi A4 and Audi A5 as a running change. Vehicles built before the changeover may only have Climatronic Control Module -J255- display and control head with part number 8T__ 820 043 installed (for vehicles with a high voltage system only the versions with part number 8R1 820 043). Vehicles manufactured after the changeover may only have the Climatronic Control Module -J255- display and control head with part number 8K_ 820 043 installed. Refer to the Parts Information and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
When the "Comfort" A/C system is installed, the Climatronic Control Module -J255- with part number 8T_ 820 043 (with part number 8R1 820 043) -A-) and with part number 8K_ 820 043 -B- can be differentiated as follows: At the start of production of the Climatronic Control Module -J255- -A- (part number 8T_ 820 043/8R1 820 043), the seat heating and ventilation are controlled by buttons -C- and the rotary switch. From the vehicle version changeover (from MY 12 as a running change), the installed Climatronic Control Module -J255- -B- (part number 8K_ 820 043) has two separate buttons -D and E- which operate the seat heating and seat ventilation. The location of the buttons -F and G- is different between both versions.
The seat heating and seat ventilation can be adjusted separately to 3 settings via the respective buttons with the introduction of the Climatronic Control Module -J255-, version -B-. Refer to the Owner's Manual.
When installed on the "Basis" A/C system, the Climatronic Control Module -J255- with part number 8T_ 820 043 (with part number 8R1 820 043) -A-) and with part number 8K_ 820 043 -B- can be differentiated as follows, for example: Both versions -A and B- can be differentiated by the rotary adjuster (version -B- with a chrome ring) and by the seat heating buttons. The seat symbols in the buttons -C and D- point in different directions on the Climatronic Control Module -J255- -A- installed from start of production. For the Climatronic Control Module -J255- -B- installed from the vehicle version changeover (from MY 2012 as a running change), the seat symbols in the buttons -C and D- point in the same direction
The seat heating can be adjusted to 3 settings via the respective buttons with the introduction of the Climatronic Control Module -J255-, version -B-. Refer to the Owner's Manual.
Updated Fresh Air Blower Control Module -J126-, Fresh Air Blower -V2-, Climatronic Control Module -J255- A/C display and control head, Vehicle Electrical System Control Module -J519-, Comfort System Central Control Module -J393-, Air Quality Sensor -G238- and A/C units are being installed as a running change from MY 2012 (depending on the vehicle version). Pay attention to the correct version and allocation of these components. Refer to the Parts Information and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
If the allocation or adaptation of the Climatronic Control Module -J255- to the Fresh Air Blower Control Module -J126- (with the part number 8K0 820 521 or 8T0 820 521) is not according to the specification, then the Fresh Air Blower -V2- is not regulated by the Fresh Air Blower Control Module -J126-. There may not always be an entry in the DTC memory even though the activation of the Fresh Air Blower -V2- is not OK. Make sure the Climatronic Control Module -J255- is adapted correctly. Refer to the Parts Information and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
At the start of production, the Humidity Sensor -G355- was only installed on the "Convenience" A/C system. Since the introduction of the Start/Stop System from MY 2010, the Humidity Sensor -G355- is also being installed in vehicles with the "Basis" A/C system and this optional equipment.
The Comfort System Central Control Module -J393- or the Data Bus On Board Diagnostic Interface -J533- evaluates the measured value from the Humidity Sensor -G355- for vehicles manufactured before the version changeover (except for the Audi Q5 hybrid). The Vehicle Electrical System Control Module -J519- evaluates the measured value from the Humidity Sensor -G355- on vehicles manufactured from the product changeover (and on all Audi Q5 hybrids). Refer to, Electrical Equipment and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
Depending on time period of production (from MY 2012 as a running change) and vehicle version, the Humidity Sensor -G355- no longer operates as an individual part in the DTC memory. On these vehicles, the Rain/Light Recognition Sensor -G397- is displayed as the fault location in the event of a deviation on the Humidity Sensor -G355-.
There is a label -A- on the outside of the A/C unit with a part number -B- that tells which version is installed. Refer to the Parts Information.
The part number -B- on the label -A- can be read, for example, when the CD changer is removed (depending on the vehicle equipment level). Refer to CD CHANGER, REMOVING AND INSTALLING .
As a running change from MY 2012, there are different versions of the Coolant Recirculation Pump -V50- (Water Pump -V36-) installed, depending on the vehicle version, on the engine and on the time period of production. How these pumps are activated is also different. From the start of MY 2012, pumps, which were controlled by a 500 Hertz signal (500 pulses per second), are replaced by 100 to 500 Hertz signal pumps. Pumps, controlled by a variable signal, also have a diagnostic function and are controlled by the engine control module. Check for the correct allocation using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. Refer to Wiring Diagram and to the Parts Information.
- An A/C compressor with an A/C Clutch -N25- is installed as a running change on certain 4-Cylinder vehicles from MY 2012.
The A/C clutch turns off the A/C compressor drive completely under certain conditions (for example "ECON"). The correct Climatronic Control Module -J255- version must be installed and coded correctly so that the A/C Clutch -N25- can be activated by the Climatronic Control Module -J255- display and control head. Refer to the Parts Information and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
So that the A/C Clutch -N25- can be activated by the Climatronic Control Module -J255- display and control head, only one Climatronic Control Module -J255- must be installed on these vehicles that has the necessary functions to activate the A/C Clutch -N25- (Climatronic Control Module -J255- with part number 8K_ 820 043 and index "K" cannot, for example, activate an AA/C Clutch -N25-). A Climatronic Control Module -J255- with part number 8K_ 820 043 and index "AA" can, for example, activate the A/C Clutch -N25-. Instead of a Climatronic Control Module -J255- with part number 8K_ 820 043 and index "K", a version with index "AA" (existing function for activating the A/C Clutch -N25- is not used) or a version with index "AF" (existing functions for activating the A/C Clutch -N25- or for vehicles with a high voltage system are not used) can be installed. Refer to the Parts Information. The coding of the Climatronic Control Module -J255- turns off or activates the necessary functions for the respective vehicle using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
- In MY 2014 and from MY 2015, a revised Climatronic Control Module -J255- display and control head is being installed as a running change (introduction depending on model and version). Pay attention to the allocation. Refer to the Parts Information.
Exact launch date is open. The Climatronic Control Module -J255- is differentiated, for example, by the button AC (part number 8K_ 820 043 up to index "AL") or the button A/C (part number 8K_ 820 043 starting with index "AM" or "BA"). Refer to the Parts Information.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.