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Pump/Valve Unit






Pump/Valve Unit

CAUTION!
Even when the engine is cold, both pump/valve unit valves can be hot.

When the ignition is on, the valves of the pump/valve unit (Left Heat Regulation Valve (N175) and Right Heat Regulation Valve (N176)) are continually activated depending on the temperature set at the Climatronic Control Module (J255) A/C control head. For this reason, the valve may be warm or hot even when the engine is cold.

If Coolant Pump (V50) causes noise, check cooling system for complete bleeding (air in coolant circuit may cause noise) before removing pump-valve unit:

Valves of pump valve unit are open when deenergized. If power supply or valve connection to the Climatronic Control Module (J255) A/C control head is interrupted, heat output of the A/C unit cannot be regulated (the A/C system heats constantly).

Both valves of the pump/valve unit (Left Heat Regulation Valve (N175) and Right Heat Regulation Valve (N176)) are reversed in left or right drive vehicles (differing connections ).

Under certain ambient conditions, if there are complaints of odd noises from the heat exchanger or poor heat output from the A/C system (an error may be stored at the Coolant Pump (V50) Check the pump/valve unit connection in the coolant circuit. If air bubbles are visible in the upper connection of the coolant expansion tank while the engine is running, also check the coolant expansion tank to ensure it is the correct version.

For complaint "poor heating performance", before removing pump-valve unit, check the following:

- The connection of the pump/valve unit 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).

- The cable routing to the Coolant Pump (V50) 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).

- Check that there are no air bubbles in the coolant circuit and bleed again if necessary.

- Check the heating performance of the A/C system => [ Ventilation System Heat Output and Pump Valve Unit Function, Checking ] Ventilation System Heat Output and Pump Valve Unit Function, Checking.

Special tools, testers and auxiliary items required

Hose clamps up to dia. 25 mm (3094) or hose clamps up to dia. 40 mm (3093)

Cooling system tester (V.A.G 1274) (and corresponding adapter)

Removing

- Switch off ignition.

- Remove the plenum chamber cover.

CAUTION!
Even when the engine is cold, both pump/valve unit valves can be hot.

- If necessary, remove the dome brace (not present in all vehicles).

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

- Clamp off coolant hose - A - (return from the A/C unit heat exchanger to the engine) e.g. using hose clamps up to 25 mm dia. (3094).





- Remove nuts - A - and - B - (torque of 4 Nm).





- Mark the assignment of coolant hoses - A - (supply to left heat exchanger) and - B - (supply to right heat exchanger).





- Disconnect connector - D - to the Left Heat Regulation Valve (N175) and Right Heat Regulation Valve (N176).

- Disconnect connector - E - to the Coolant Pump (V50).

- Clamp off coolant hose - C - (from the engine to the Coolant Pump (V50)) e.g. using hose clamps up to 25 mm dia. (3094).

- Remove coolant hoses - A -, - B - and - C - from the pump/valve unit connections.

- Remove the pump/valve unit - C -.





Installing

The Coolant Pump (V50) can only be operated after bleeding the coolant circuit (running the Coolant Pump (V50) dry will destroy it).

Both valves of the pump/valve unit (Left Heat Regulation Valve (N175) and Right Heat Regulation Valve (N176)) must be open to bleed the coolant circuit (they are open when they are not activated).

If the ignition is started with the pump/valve unit connectors disconnected, the errors Coolant Pump (V50), Left Heat Regulation Valve (N175), and Right Heat Regulation Valve (N176) are detected and stored by the Climatronic Control Module (J255) A/C control head.

Installation is carried out in the reverse order, when doing this note the following:

- Reinstall removed components in reverse order of removal (except the plenum chamber cover).

- After installation, check the grommet between engine compartment and plenum chamber at the coolant hose - C - for proper seating.





- Check the pump/valve unit, it may not make contact with other components (noises).

- Bleed the coolant circuit.

- After bleeding the coolant circuit, connect the connectors - D - to the Left Heat Regulation Valve (N175) and Right Heat Regulation Valve (N176), and - E - to the coolant pump Coolant Pump (V50).

- Clean coolant residue from the plenum chamber.

- Install the remaining removed components again in reverse order.

- Check the DTC memory for the Climatronic Control Module (J255) A/C control head and erase any faults displayed if necessary.

Pump Valve Unit Bracket, Removing and Installing

- Remove pump valve unit => [ Pump/Valve Unit ] Pump/Valve Unit.

Holder - A - differs in left-hand steering and right-hand steering vehicles.





The rubber elements - B - are installed between the pump/valve unit - C - and the holder - A -. They are intended to inhibit the noise produced by the pump/valve unit - C - to be transferred to the vehicle body.