Heater Control Valve: Service and Repair

Left and Right Heat Regulating Valves

Special tools, testers and auxiliary items required

• Hose clamps up to 25 mm diameter (3094) (quantity: 3)

CAUTION!
There is a risk of burns.

• The heat regulating valve unit may be warn or hot even when the engine is cold because it is continuously activated when the ignition is on depending on the temperature setting on the Climatronic Control Module (J255).

• The Left Heat Regulating Valve (N175) and Right Heat Regulating Valve (N176) are open without current. If the voltage supply or the connection to the Climatronic Control Module (J255) are interrupted, the A/C system heat output may not be regulated correctly (the A/C system heats constantly).

If there is a complaint about poor heat output, check for the following before removing the heat regulating valves:

• Connection of the heat regulating valves and return from the A/C unit heat exchanger to the engine coolant circuit (supply and return lines connected to the engine correctly). If the connections have been switched, the engine coolant pump works against the Coolant Pump (V50).

• Line routing to the coolant pump to see if they are switched (+ and -). If the connections are switched, the pump runs in the wrong direction (and works against the engine coolant pump).

• Coolant circuit bleeding; bleed it again if necessary.

• Climate control system heat output, refer to => [ Heat Output, Checking ] Heat Output, Checking.

Removing

- Switch off ignition.

CAUTION!
There is a risk of scalding from hot steam and coolant.

• The refrigerant system is under pressure when the engine is warm.

• To reduce the pressure, cover the coolant reservoir cap with cloths and open it carefully.

- Open the coolant reservoir cap.

- Remove the center tunnel cover - 1 -.





- Remove the driveshaft.







CAUTION!
There is a risk of burns.

• The heat regulating valve unit may be warn or hot even when the engine is cold because it is continuously activated when the ignition is on depending on the temperature setting on the Climatronic control module.

- Mark the assignment of coolant hoses - F - (supply to left heat exchanger) and - B - (supply to right heat exchanger) so they can be installed later.

- Clamp the coolant hoses - A, B and F - off with hose clamps (3094).

- Remove the line bracket - C - from the threaded pin.

- Remove the nut below.

• Tightening specification 8 Nm.

- Disconnect the electrical connector - D -.

- Remove the coolant hoses - A, B and F - from the heat regulating valve unit - E -.

- Remove the heat regulating valve unit.

Installing

Installation is done is reverse order, observe the following:

• The coolant pump can only be operated after bleeding the coolant circuit (running the coolant pump dry will destroy it).

• Both heat regulating valves must be open to bleed the coolant circuit (they are open when they are not activated).

- Disconnect the electrical connectors on the heat regulating valve unit and the coolant pump.

- Bleed the coolant circuit.

- Connect the connectors to the coolant pump and the heat regulating valve unit.

• If the ignition is switched on with the connector disconnected, the Climatronic control module will detect and store malfunctions for the coolant pump and heat regulating valves.

- Install the driveshaft.

- Install the center tunnel cover.

After finishing the repairs, perform the following work on the Climatronic Control Module (J255) using Vehicle diagnosis, testing and information system VAS 5051/ in the "Guided Fault Finding" function:

- Check the DTC memory and erase any malfunctions shown.

- Perform the output diagnostic test mode.