2007 Audi S4 AC Evaporator Replacement Cost

As compressed refrigerant reaches the evaporator, it passes through an expansion valve. This rapidly depressurizes the refrigerant, causing its temperature to drop dramatically. Now a cold gas, the refrigerant passes through the evaporator, causing that part's metallic core to become extremely cold. The cold evaporator is in the airflow path of the blower motor, and it cools down the air that blows into the car's cabin.

Anytime the AC evaporator goes bad, the air from the vents will be warmer than expected. This is because a clogged or leaking evaporator won't get enough refrigerant to cool the air. In some vehicles, there may be some type of warning like a blinking AC switch.

Vehicles with a bad evaporator can be driven, but they won't be comfortable when it's hot outside. In extremely hot climates such as deserts, not having a working air conditioner could be dangerous for children and seniors.

Most cars will never need a new evaporator, but there are factors that can shorten its life. The evaporator is metallic, and if there's moisture in the air conditioning system, that moisture can cause corrosion. Likewise, a leaking heater core can get coolant on the evaporator, potentially ruining it. Additionally, the rubber seals for the AC lines connecting to the core may cause the evaporator to leak, in which case the technician may recommend replacement.

Any number of problems in the air conditioning system can cause the same symptoms. A servicing technician will need to examine the whole thing to make the right diagnosis. Typically, the evaporator coil would be suspected after testing for leaks, especially if it's clear there's a leak even if it can't be visibly detected. Also, if the technician finds that the pressures in the system are too extreme, the evaporator may be suspected of a clog.

The air conditioning system will have to be evacuated and the evaporator will need to be accessed. This is usually done through a service port near the passenger foot well or by removing the dashboard. The evaporator can be removed by disconnecting all its mounting hardware and using specialized tools to remove the air conditioner lines. Replacing the evaporator is a matter of refitting the lines, replacing any components removed to access the evaporator, and recharging the system for testing.

We recommend avoiding the use of any off-the-shelf air conditioning repair additives. These additives are only temporary fixes, if they work at all, and can cause damage to air conditioner refrigerant evacuation machines. Also, never attempt to vent refrigerant into the air — this is harmful to the environment and can cause chemical burns. 

When it comes to servicing the air conditioner, it's best left to the pros. They will have the equipment needed to safely evacuate refrigerant and refill the system.