Rear Heating and A/C Unit

Rear Heating and A/C Unit

• Currently in this vehicle, all motors are identical in construction. During the basic adjustment, the control motors are assigned and adapted corresponding to the switching sequence of the wiring. If this sequence does not conform the specification, the control motors will adapt incorrectly and the door control will be wrong. Refer to => [ A/C Control Motor Block Diagram ] A/C Control Motor Block Diagram.

• Perform the basic setting for the A/C system after installation of the rear A/C unit using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• Using the output diagnostic test mode and basic setting functions, the activation of A/C system electrical components can be tested if necessary (for example allocation test) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• After installing a new control motor, check the activation via the rear A/C display control head (E265) and the function of the control motor using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• For rear A/C unit - C - to be removed, the entire center console including the base support of center console - A - and insulation mat - B - installed between the base support and rear A/C unit - C - must be removed.






Removing

- Switch off the ignition.

- Remove the driver and front passenger seat.

- Remove the base support of center console - A - and insulation mat - B -.

- Remove the rear seats or rear bench seat and the rear floor covering.

- Drain the refrigerant circuit.

- Release pressure in cooling circuit by opening cap on coolant expansion tank.

• The heater core installed in the rear A/C unit remains in the vehicle during removal of the A/C unit. It is only removed from the A/C unit and tilted to the side, refer to => [ Rear Heater Core Removal From A/C Unit ] Rear Heater Core Removal From A/C Unit.

• Coolant only unintentionally escapes from the coolant circuit when the heater core is removed without pressure with the cap open on the coolant expansion tank.

• A/C system malfunctions in the case of interchanged temperature sensors, control motors and/or connectors, refer to => [ A/C Control Motor Block Diagram ] A/C Control Motor Block Diagram.

• The control motors and connectors are identical. If they are installed or connected incorrectly, the corresponding doors cannot be properly adapted and/or activated.

• Clearly label control motors and connectors prior to removal to prevent incorrect installation.

• Rear A/C unit - A - can also be removed with air duct - D - installed (from the front A/C unit to the rear A/C unit). However, due to the easier execution, removal is described here with air duct - D - removed.






• Depending on the version, rear A/C unit - A - can additionally be secured with a bolting point to the center tunnel (if necessary, remove hexagon nut - C -).

- Disconnect harness connector - B -.

- Remove connectors - C - from the rear fresh air blower control module (J391).






- Remove bolts - A -.






- Push air duct - C - forward (to the front A/C unit). Then lift air duct - C - at the back and remove in the - direction of the arrow -.

- Clearly label the line routing to the 4 temperature sensors - A - through - D - on the air ducts.






Interchange of the wire connections to the temperature sensors or the connectors at the control motors results in problems regarding the regulation of the A/C system.

• Interchanged connectors at the control motors or the temperature sensors are not identified as malfunctions by the rear A/C display control head (E265).

• Prior to disconnecting connectors or removing electrical components, clearly label them in order to rule out confusion.

- Remove the 4 temperature sensors - A - through - D - from the air ducts (- A -, refer to=> [ Left Rear Upper Body Vent Temperature Sensor (G635) ] Left Rear Upper Body Vent Temperature Sensor (G635), - D -, => [ Right Rear Upper Body Vent Temperature Sensor (G636) ] Right Rear Upper Body Vent Temperature Sensor (G636), - B -, => [ Left Rear Footwell Vent Temperature Sensor (G637) ] Left Rear Footwell Vent Temperature Sensor (G637), and - C - => [ Right Rear Footwell Vent Temperature Sensor (G638) ] Right Rear Footwell Vent Temperature Sensor (G638)) and secure together with the corresponding lines to the rear A/C unit so that they are not it the way and are not damaged during removal of A/C unit - E -.

- Cover the air ducts in the rear passenger compartment so that they are not compressed or damaged during further work steps.

- Remove hexagon nut - A - on the connection point of the refrigerant lines.






• If shift relay lever - B - is positioned so that hexagon nut - A - is not accessible, remove the rear recirculation door motor (V421) => [ Rear Recirculation Door Motor (V421) ] Rear Recirculation Door Motor (V421).

- Remove heater core - A - from the rear A/C unit and place it in the area of the right rear footwell so that the heater core and the coolant lines are not in the way and are not damaged during the further work steps, refer to => [ Rear Heater Core ] Rear Heater Core.






• The heater core can be removed from the A/C unit with the rear A/C unit installed without needing to open the coolant circuit (for example to remove and install the rear A/C unit).

• The rear heater core remains in the vehicle when removing the rear A/C unit (so that the coolant circuit does not need to be opened)

• For coolant lines - C - to heater core - A - (see above figure) to be removed together with the rear A/C unit, the heat shield in center tunnel - B - must be removed.






• The coolant lines to the heater core are connected via coolant hoses, which are routed in the center tunnel above driveshaft - D - behind heat shield - A -, to the coolant circuit.

• To remove heat shield - A - in the center tunnel, exhaust system - C - with the center muffler and driveshaft - D - must additionally be removed depending on the vehicle.

- Detach rear A/C housing - D - from holding points - A - and air ducts - E -.






• Grommets - B -, - C - and - F - shown in this figure are only installed in a vehicle with a rear air distributor housing. They may not be installed in vehicles with a rear A/C unit.

- Detach the refrigerant lines to the evaporator on supply location - C - from refrigerant lines - H - in the center tunnel.






- Detach the coolant lines to heater core - F - from brackets - G - on A/C unit - A - and remove rear A/C unit - A -.

• Refrigerant lines - H - (from the rear expansion valve through the center tunnel) and threaded stud - J - remain installed.

• When the A/C unit is removed, refrigerant lines - H - and threaded stud - J - are held in position by a bracket which is glued in place from below in the center tunnel, refer to => [ Rear A/C Unit Expansion Valve To Evaporator Refrigerant Lines, Replacement ] Rear A/C Unit Expansion Valve To Evaporator Refrigerant Lines, Replacement.

- Close the open connection on the refrigerant lines in the center tunnel and on the A/C unit with suitable caps (to prevent dirt and moisture from entering).

Installing

Installation is carried out in the reverse order while observing the following.

- Check grommets - A - on coolant line - B - for proper seating and damage.






- Check foam seals - L - on both condensation water drains - M - for damage and proper seating.

- Check both condensation water drains - M - on the rear A/C unit for damage and contamination.

- Check both openings in center tunnel - N - for condensation water drains - M -. They must not be closed (the condensation water must be able to flow freely out of condensation water drains - M - with the rear A/C unit installed). The heat shield installed under both openings in center tunnel - N - must be a sufficient distance from the floor plate. The condensation water must flow freely.

- Check foam seal - J - on the rear A/C unit for damage and proper seating.

- Check the connection of refrigerant lines - C - (to the evaporator in the rear A/C unit) and refrigerant lines - G - and - H - for contamination and damage.

• Even slight damage (a scratch) or a little bit of dirt (a hair) can cause leakage at a connection.

- Replace O-ring seals - E - and - F -; refer to the Electronic Parts Catalog.

- Coat the O-ring seals with refrigerant oil prior to installation, refer to => [ Refrigerant Circuit O-rings ] Refrigerant Circuit O-rings.

- Check the retaining plate that holds refrigerant lines - G - and - H - and threaded stud - D - in place for secure seating.

If the rear A/C unit is installed in a careless manner, the retaining plate that holds refrigerant lines - G - and - H - and threaded stud - D - in place can detach from the vehicle.

• This retaining plate is adhered to the floor plate. If it is pressed away during installation of the rear A/C unit, attachment of the refrigerant lines may require significant extra work, refer to => [ Rear A/C Unit Expansion Valve To Evaporator Refrigerant Lines, Replacement ] Rear A/C Unit Expansion Valve To Evaporator Refrigerant Lines, Replacement.

• Pay particular attention to this connection when installing the rear A/C unit and work carefully.

• Grommets - B -, - C - and - F - are only present in vehicles with an air distributor housing. They may not be installed in vehicles with a rear A/C unit.






• If a grommet - F - is installed in one of the two openings for the condensation water drains in a vehicle with a rear A/C unit or if these opening are closed from the bottom, for example by underbody sealant, condensation water cannot flow out of the vehicle, refer to => [ Rear Condensation Water Drains, Checking ] Rear Condensation Water Drains, Checking.

- Check holding points - A - for correct installation in the center tunnel and for damage.

- Check the ball heads on rear A/C unit - D -, which are inserted in holding points - A -, for damage.

- Check the outlets at rear A/C unit - D -, which are inserted in air ducts - E -, and air ducts - E -, for damage and contamination.

• Damaged or improperly joined components can result in noises during operation of the A/C system.

- Carefully install rear A/C unit - A - in the refrigerant lines to the evaporator on supply location - C - on refrigerant lines - H - in the center tunnel.






- Check both openings - E - in the center tunnel (for the condensation water drains). They must not be closed.

- Check holding points - D - for correct installation in the center tunnel and for damage.

- Insert the coolant lines to heater core - F - in brackets - G - on A/C unit - A -.

- Insert rear A/C unit - D - in holding points - A - and air ducts - E -.






- Install hexagon nut - A - on the connection point of the refrigerant lines (tightening torque: 20 Nm).






- Reinstall the parts removed from the passenger compartment in the reverse order.

- Evacuate and fill the refrigerant circuit.

- Perform the basic setting and the output diagnostic test mode of the A/C system using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• In this vehicle, the control motors are equipped with electronics. During the basic setting, a new control motor learns its position on the A/C unit and can then be activated by the rear A/C display control head (E265) / the Climatronic control module (J255) (currently all control motors are identical). Check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• During the basic setting, the control motors are assigned and adapted corresponding to the switching sequence of the wiring. If this sequence does not conform with the specification, the control motors will adapt incorrectly and the door control will be wrong, refer to => [ A/C Control Motor Block Diagram ] A/C Control Motor Block Diagram.

- Install the remaining removed components.

- Check the event memory of the Climatronic control module, and the rear A/C display control head and erase any displayed malfunctions using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

- Operate the A/C system after filling the refrigerant circuit, refer to => [ A/C System Operating After Filling Refrigerant Circuit ] A/C System Operating After Filling Refrigerant Circuit.

• Note the information regarding operation of the A/C system after filling.

- Check the function of the A/C system using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.