Coolant System, Bleeding

Coolant System, Bleeding

• Cooling circuit is under pressure. When opening coolant expansion tank, hot steam or hot coolant may flow out, therefore cover sealing cap with a cloth and open carefully.

• The removal of A/C system components (except for compressor in vehicles with 8 cylinder FSI engine) is described in this Repair Manual in such a way that only a small amount of air enters the cooling circuit, therefore it is not necessary to bleed cooling circuit completely after removing and installing these components.

• If, however, a large amount of coolant flows out due to a different complaint, for example, due to a leaking hose, compressor replacement on vehicles with 8 cylinder FSI engine or after coolant hose replacement, the cooling system is to be bled completely using Cooling System Charge Unit (VAS 6096).

• After bleeding and charging the cooling circuit using Cooling System Charge Unit (VAS 6096) , the section of the cooling circuit with the A/C system (heater core and associated hoses) is to be post-bled as described below.

Section Of Cooling System With A/C System, Bleeding

- The cooling system is essentially filled with coolant, there are only a few air bubbles in only a few locations of the cooling circuit.

• Since it was pre-filled when installing A/C system components (for example, heater core), only a small amount of air is in the cooling circuit, therefore it is sufficient to set the A/C system to maximum heat output when engine is warm (so that recirculation pump is actuated) and to let engine run for a few minutes at increased idle speed (approximately 2000 RPM) in order to bleed the cooling circuit completely.

• When bleeding coolant system, take special care to ensure complete bleeding of heater cores. If air bubbles remain in heater cores, there may be complaints made by customers about insufficient heating performance in winter, or different air temperature from vents at same setting in regulated mode, refer to => [ Heating Performance Of A/C System, Checking ] Heating Performance Of A/C System, Checking.

Bleeding

- Fill coolant into coolant expansion tank up to top marking.

- Start engine and let it run until it reaches operating temperature.

- Set the Climatronic control module (J255) (and the Rear A/C display control head (E265) , if present) to maximum heat output (for example, temperature pre-selector on HI) for the driver side and front passenger side.

- Set the Climatronic control module (and the rear A/C display control head, if present) to fresh air blower speed approximately 30% of maximum performance.

- Fresh Air Blowers (V2) (and Rear Fresh Air Blowers (V80) , if present) operate at a speed in the lower performance range.

- Let engine run approximately 2 minutes at increased idle speed (approximately 2000 to 2500 RPM).

- Switch off ignition and check coolant level in coolant expansion tank, add coolant if necessary.