Tech Article Title Author Date
Understanding the Climate Control System Christian J. Long 1998

There has been much confusion among A4 owners regarding the Automatic Climate Control. I have written these instructions due to the owner's manual not being very detailed in its operation.

The climate control system in the Audi A4, which debuted in the '92 Audi 100 and the '93 Audi 90, is an all new design that replaces the older automatic climate control system that was a GM derived unit, used on Audis from the mid 1980's to 1992. The newer climate control system is far better than the one it replaces in that you can be in full manual mode unlike the old one, it is much friendlier, and looks to be up to Audi's standard of aesthetics. You can also use this system to call up over 60 diagnostic readings such as engine coolant temp in Celsius and a digital display of vehicle speed in kph (see separate FAQ about how to call up and read codes).

There are 3 modes you can be in with the climate control system; Auto, Auto/man, and Man:

To be in AUTO MODE (fully automatic), you hit the "auto" button. There word "auto" lights up in the left window of the system displays (and the word "man" WILL NOT be lit in the right window). Now you can set the cabin temp you want by the "+" and "-" buttons. The system will vary the fan speed and vent location (dash, floor or defrost) to bring the cabin to the desired temperature. You do nothing but dial in the temp, and the system takes care of the rest. In full automatic mode, the compressor will automatically be turned off if the outside temperature is below a certain temperature, but you can still be in auto mode and turn the compressor on or off.

In AUTO/MAN MODE, you can vary the fan speed, but everything else is controlled automatically to reach the displayed temp. From Auto mode, if you adjust the fan speed buttons "+" or "-", you will see the word "auto" lit up in the left window, and "man" will then light up in the right window. Use this in auto mode when you want to turn up or turn down the fan speed, but still have the car automatically adjust other functions to reach the desired temperature. To get back to full auto mode, just hit the auto button again.

In pure MANUAL MODE, you control where the air comes from (dash, floor, defrost), and what fan speed. Press one of the vent location buttons (I always use dash vents in manual AC), and you will see the "man" word light up in the right window, and the "auto" word will NOT be lit up in the left window. Next press "+" or "-" on the fan speed. Once you set the fan speed, compressor on/off and vent location, it will never vary from that setting. The fan speed will vary if you are in manual mode and do not adjust the fan speed, once you hit one of the fan speed buttons, it will not change from that setting.

For some reason, Audi only lets you recirculate the air when the compressor is on in the US vehicles. Many times I wish that I could recirc the air when the AC isn't on (when I get behind a diesel car), but it will not let you choose that option. Currently there is no known way to bypass this recirculation cutout. European cars do have the option to use the recirculation feature with or without the compressor being on. Also note that the recirculation resets every time you turn off the car, so if you like this option, you will have to select recirculation every time you start the car. The recirculation feature will be selected by the climate control system when you set the temperature to a cool setting. The recirculation symbol will not light up, but you can hear the flap move to stop the flow of outside air.

The defrost feature can be access by two methods. The first and simplest way to defrost the front windshield is to press the defrost symbol in the upper left of the climate control system. This turns the compressor on, sets the fan speed on high, and diverts the air to the defrost vents on top of the dashboard. You can also defrost the front windshield by setting all these conditions manually when in manual mode.

To turn the climate control system completely off, press and hold the fan speed button. The fan speed display will decrease until only one bar is left lit up on the display. You will then have to press the fan speed button one last time to decrease the fan speed down to stop.

You can change the climate control to be in Fahrenheit or Celsius degrees. To switch, press the recirculation button and hold, at the same time, press the temperature "+" button. I do not know of any way to change the outside temperature display in the instrument pod.

When using heat, it is important to realize that the fan will only come on when the engine coolant is sufficiently warm enough to provide heat for the cabin. When you first start the car on a cold day, the fan will not come on immediately. Once the heater core has warm coolant flowing through it, the fan will turn on and start warming the cabin.

The sensors that control the climate control unit are the sun sensor and cabin temperature sensor. The sun sensor is the dome shaped unit located in the middle of the defrost vents on top of the dash. This adjusts the climate control system to compensate for the hot sun glaring into your car. The cabin air temperature sensor measures the cabin temperature by the small vent that is located above the climate controls.

It is recommended that if you live in a climate that experiences a cold winter, you should switch on your compressor about once a week for several minutes during the winter months to keep the compressor from becoming damaged from such a long period without use.

I also recommend turning your compressor off when the outside temperature is below 70 degree Fahrenheit. If you are in "auto" mode, the system will turn the compressor on, even though you do not need it at such a cool temperature. Just press the snowflake button to turn the compressor off.

The AC compressor robs power and performance; you will notice a decrease in miles per gallon and acceleration. If you do not need the compressor on, make sure it is off. The system will sometimes turn it on even though it is not required in cool weather. Using the compressor needlessly will cause it to fail early and cause the engine to waste extra gasoline.

When dialing in a temperature setting or fan speed, refrain from hitting the "+"or "-" buttons multiple times. If you just press and hold the buttons, the setting will adjust until you stop applying pressure on the button.

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