As we move through spring and into summer, temperatures begin to heat up in most of the country. This is a time many drivers begin using the cool settings on their vehicle’s climate control system — only to find the air conditioning unit not functioning properly. As the temperatures outside rise, so too, will the number of customers in your shop with A/C-related problems.

This fix revolves around some late-model Audis, where the A/C blower operates, but the system does not cool the cabin.

Models affected:
• 2004-’10 A8
• 2005-’11 A6
• 2008-’11 A5, S5
• 2009-’11 A4
• 2010-’11 A5 Cabriolet

Condition:
The vehicle’s air conditioning is inoperative. The HVAC blower functions normally.

Technical Background:
It has been reported that the A/C Pressure/ Temperature Sensor G395 leaks refrigerant. This will cause Sensor G395 to show an incorrect or implausible value when reading MVBs (measuring value blocks).

An incorrect signal or a low refrigerant level in the system can cause the air conditioning compressor to deactivate.
In other cases, the LIN cable connecting the J519 Central Electrics Control unit to Sensor G395 has been found to be pinched or cut.

This affects the A4/54, A5/55 Coupe and Cabriolet, and Audi Q5 vehicles. However, the A6 and A8 are not affected by this type of failure.

Tip: Sensor G395 is a LIN slave of Vehicle Electrical System Control Module J519. Vehicle Electrical System Control Module J519 transfers the information provided by the sensor via the comfort data bus to Climate Control Module J255.

Production Solution:
According to Audi, an improved A/C Pressure/ Temperature Sensor G395 was introduced into series production and the wiring manufacturer’s processes were optimized.

Service:
For A4/S4 (8K), A5/S5 Coupe/Cabrio (8T/8F), Audi Q5, A6 and A8:

If DTCs are stored in the J255 Climate Control Module for the G395 pressure sensor, then check the system pressures and refrigerant volume.

– If system pressures and refrigerant volume are low, check for refrigerant leaks at G395. If a leak is found, then replace the G395.

– If the system pressure and refrigerant volume are correct, perform guided fault-finding. If an implausible pressure value is found in MVB 1, field 4, then replace G395.

A4/S4, A5/S5, Q5, A6: Use improved part number 4H0 959 126.

A8: See ETKA for part number.

Tip: Install only the improved G395.

Only for A4/S4 (8K), A5/S5 Coupe/Cabrio (8T/8F) and Audi Q5:

1. Check for these three DTC codes:

• DTC (Vehicle Electrical System Control Module – J519 – Please check DTC memory) in Climate Control Module J255, address 08.

• DTC (A/C Pressure/temperature Sensor – G395 – Incorrect Signal) in Climate Control Module J255, address 08.

• DTC (A/C Pressure/temperature Sensor – G395 – No signal/communication) in Vehicle Electrical System Control Module J519, address 09.

Perform steps 2-6 only if all three DTCs are stored.

Tip: The LIN cable connecting the J519 Vehicle Electrical System Control module to the G395 Pressure Sensor could be pinched or cut if all of the codes are stored.

2. Check the LIN cable connecting the J519 Central Electrics Control unit to the G395 pressure sensor according to guided fault-finding.

3. Check the wire terminals in the connector at the G395 pressure sensor for proper attachment, possible corrosion and for any pins that may be pushed back or widened.

4. Check to make sure there is proper voltage going to the sensor and verify the ground is not intermittently open (wiggle test).

5. Check the integrity of the wire harness.

There are two known sections in the wiring harness that can be affected, but the potentially affected areas are not limited to these two known sections. One of the known sections is in the driver’s footwell area where the wire harness enters the interior of the car from the engine bay.

See Figure 1.

The second known section is in the wire harness located under the driver’s side headlight.

See Figure 2.

6. If a cut wire is found, then install an overlay wire for the LIN bus signal. Do not attempt to repair the existing wire harness.

a. Route the new LIN bus wire so that it enters the interior of the vehicle through the driver’s side ­fender/lower A-pillar area through the grommet. 

See Figures 3 and 4.

Tip: Do not route the wire through the same opening used by the existing wire harness.

b. Seal off the opening around the wire with Butyl sealant to prevent water intrusion.

Courtesy of ALLDATA.