How do I check for an evaporator leak?
Short answer: Sample at the evaporator drain or the center vent with the blower off and the system charged, look for dye at the drain, and confirm before replacing the evaporator.
The evaporator is buried in the dash, which makes it the hardest part to check and the most expensive to replace. Start by testing indirectly. With the system charged and the engine off, switch the blower off for several minutes so refrigerant can collect in the case. Then sample with an electronic detector at the drain tube under the vehicle, or at the vent closest to the evaporator.
If the system has dye, shine a UV light at the drain outlet and the condensate it drips. Some technicians use a borescope through a blower motor or resistor opening to look at the core directly.
Rule out the expansion valve, lines and fittings near the firewall first, since a leak there can look like an evaporator leak. Confirm with more than one method before tearing down a dash. Disconnect and protect airbag connectors as the maker directs when removing dash parts.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.