Coolant Circuit, Bleeding
Coolant Circuit, Bleeding
• The removal of A/C system components is described in this repair information in such a way that only a small amount of air enters the coolant circuit. Therefore, it is not necessary to bleed the coolant circuit completely after removing and installing these components.
• However, if a large quantity of coolant has escaped due to another complaint, for example due to a leaking hose, the coolant circuit must be completely bled with the Cooling System Charge Unit (VAS 6096).
• After bleeding and charging the coolant circuit using the Cooling System Charge Unit (VAS 6096) , the section of the coolant circuit of the A/C system (heater core and associated hoses) is to be post-bled again via the bleeder screw - G -.
Section of Cooling Circuit With A/C System
Prerequisite
- The cooling circuit is essentially filled with coolant, there are only a few air bubbles in only a few locations of the cooling circuit.
• Since only a small amount of air entered the coolant circuit during installation of the A/C system components (for example the heater core in the front or rear A/C unit, the coolant recirculation pump (V50) , the Coolant Shut-Off Valve (N82) , etc.) and the circuit was charged again during installation of the components, only a small amount of air is in the coolant circuit. Therefore, it is sufficient to set the A/C system to maximum heating output when the engine is at operating temperature (so that the coolant recirculation pump is activated) and to run the engine for several minutes at a high idling speed (approximately 2000 RPM) to completely bleed the coolant circuit.
• When bleeding coolant circuit, take special care to ensure complete bleeding of heater cores. If there are still air bubbles in the heater cores, they may cause the customer to complain of insufficient heating performance in winter or different air temperature from vents at the same setting in control mode. Refer to => [ Heat Output and Temperature Door Activation, Checking ] Heat Output and Temperature Door Activation, Checking.
Bleeding
- Fill coolant into coolant expansion tank up to top marking.
- Start the 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 preselector on HI) for the driver side and front passenger side.
- Set the fresh air blower speed to approximately 30% of maximum output on the Climatronic control module (and the rear A/C display control head if present).
- The fresh air blower (V2) and the rear fresh air blower (V80) operate at a speed in the lower output range.
- In vehicles with a parking heater, switch it on briefly.
- 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.
• The coolant circuit is under pressure. When opening the coolant expansion tank, hot steam or hot coolant may flow out. Therefore, cover the sealing cap with a cloth and open carefully.