To cool the interior of a vehicle, the air conditioning system has to compress and expand refrigerant, changing its temperature. The air conditioner evaporator is what makes the refrigerant cold. This part is typically found underneath the dashboard.
How does an AC evaporator work?
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.
A failing evaporator can cause the A/C to stop cooling. If the evaporator leaks, there may be an odd odor when using the heater or A/C.
What are the symptoms of a bad AC evaporator?
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.
Can I drive with a bad AC evaporator?
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.
How often do AC evaporators need replacement?
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.
How are AC evaporators diagnosed?
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.
"Stop leak" compounds are not recommended, as they are a temporary solution and can damage AC components, resulting in expensive repairs.
How are AC evaporators replaced?
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.
Recommendations for related repairs
We recommend replacing the A/C drier when the A/C evaporator is replaced. The A/C drier acts as a moisture and debris filter for the A/C system and a new part will keep the repaired system clean. (This will add additional parts and labor cost to the RepairPal price estimate.)
Mercedes-Benz AC Evaporator Replacement Cost Estimates
The average cost for a AC Evaporator Replacement is between $1,771 and $2,250 but can vary from car to car.
