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Audi: HVAC Diagnostic

Troubleshooting a bothersome HVAC system may not be as hard as you think. Here are some possible causes to your problem.

By Neftali Medina - April 5, 2016
Contributors: Audiworld

This article applies to the Audi A6, A4, A3 and Q5/Q7 (2004-2010).

It really is a bother when the temperature drops and you turn your heater on, only for it to spew out the cold winter breeze. Or even in the hot summer, where it seems like your vents have small volcanoes in them. The HVAC system on your car is operated through the climate control interface on your center console. The vents themselves have a series of blend doors and valves that open as well as close to direct the air flow from either the compressor or heater core. Sometimes issues with a stuck valve or blend door can contribute to a buggy system. A leak on an A/C line, or damaged compressor, will result in a lost of cold air. Here are a few issues that can cause your HVAC system to fail.

Audi: HVAC Diagnostic

Materials Needed

  • Refrigerant
  • A/C gauge
  • Torx driver set
  • Flat head screwdriver
  • Coolant
  • Drain pan
  • Chrome cleaner

Step 1 – Check your freon

You may have a leak.

A very common problem that occurs is the air conditioner stops producing cold air. An air conditioning system, using several components, includes a compressor to pressurize a chemical called freon, and drastically lower its temperature. The surrounding air then also cools, and in turn keeps you from melting. If the system fails to be properly pressurized, such as if there is a leak present, the air will not be able to be cooled. Use the procedure below to check for leaks.

  • Purchase an A/C recharging can.
  • Connect it to the lower pressure line.
  • Check the pressure.
  • Make sure the pressure stays in the green recommended zone.

After checking the pressure, add more if necessary. If the leak is small enough, you can retain cold air for extended periods of time–until you can properly fix it.

Checking pressure in A/C lines
Figure 1. Check the pressure in the A/C lines.

If the freon looks good, then continue to Step 2.

Step 2 – Check the pump valve unit

It may be dirty.

Audi A6 models built from 2005 to 2007 have be known for having an issue with its pump valve unit; in fact, a TSB (2013833/5) was issued, recommending replacement of the old unit with a newly updated model. The problem occurs when the pump valve becomes blocked with engine debris. A new unit generally cost up to $300, but you may be able to clean the original by following the instructions listed below.

  • Remove the rear engine plastic cover.
  • Disconnect the wire clip.
  • Loosen and remove the six Torx screws.
  • Remove the valve cover.
  • Remove the valve assemblies.
  • Clean out the internal components using a chrome cleaner.
  • Properly reassemble everything.
cleaning valve assemblies for pump valve
Figure 2. Clean the valve assemblies for the pump valve.

If the pump valve unit has been replaced or is functioning properly, then keep going.

Step 3 – Check the heater core

It might be clogged.

The heater core is responsible for taking coolant from hoses that pass through it and directing it into the cabin of the vehicle. Sometimes, the hoses from the core become clogged with debris. In order to get the heat working again, you will have to flush the system.

Flushing heater core
Figure 3. Flush the heater core.

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