Coolant Circuit, Bleeding

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The removal of A/C system components is described in this repair Service 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, refer to FOR ENGINE(S) CTUA & CGXB - COOLANT, DRAINING AND FILLING , FOR ENGINE(S) CPNB - COOLANT, DRAINING AND FILLING or FOR ENGINE(S) CEUC & CRDB - COOLANT, DRAINING AND FILLING [For engine(s) CPNB] Cooling System .
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 bleed hole -arrow-.

Fig 1: Locating Bleed Hole
Courtesy of AUDI OF AMERICA, LLC

Prerequisite

Since only a small amount of air entered the coolant circuit during installation of the heat exchanger for the heater in the air conditioner, 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 -V50- 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 the coolant circuit, take special care to ensure complete bleeding of the heater core. If air bubbles remain in the heater core, customer complaints may be received about lack of heating output in winter or differences in temperature of air flowing out of vents with same setting in control mode, refer to A/C System Temperature Door Heat Output Activation, Checking .

Bleeding

Fig 2: Cooling System Tester - Adapter

Courtesy of AUDI OF AMERICA, LLC

-- Place the Cooling System Tester - Adapter VAG 1274/10 on the Cooling System Tester - Adapter VAG1274/8.

-- Fill with coolant until the coolant system tester pipe is full. If necessary, refill during the bleeding procedure, refer to FOR ENGINE(S) CTUA & CGXB - COOLANT, DRAINING AND FILLING , FOR ENGINE(S) CPNB - COOLANT, DRAINING AND FILLING or FOR ENGINE(S) CEUC & CRDB - COOLANT, DRAINING AND FILLING [For engine(s) CPNB] Cooling System .

-- Start the engine and let it run until the operating temperature is reached.

-- Set the maximum heating output for the driver- and passenger side on the Climatronic Control Module -J255- control head (for example, temperature preset on "HI").

-- Set the fresh air blower set to approximately 30% of the maximum output.

The fresh air blower operates at a speed in the lower output range.

-- On vehicles with a parking heater switch it on for approximately 30 seconds.

-- Allow the engine to run for two minutes at 2000/RPM.

-- Stop the engine and let it cool.

-- Check the coolant level.

Fig 3: Locating Coolant Reservoir Cap

Courtesy of AUDI OF AMERICA, LLC

The coolant level must be at the MAX mark when the engine is cooled.
The coolant level may be above the MAX marking if the engine is warm.