Evaporator Core

One of the most difficult leaks to find is in the evaporator core. Follow the instructions below in order to lead test the core:
1. Turn the blower fan on high for 15 or more seconds.
2. Shut off the blower fan.
3. Wait 10 minutes.
4. Remove the blower fan power module or resistor block, if accessible.
5. If the blower fan power module is not accessible, inspect the condenser drain tube for moisture.
6. If the condenser drain tube is dry, use the drain tube instead.
7. Insert the leak detector probe into the resistor/relay opening, or the blower case drain tube. If the detector goes to a solid alarm, a leak has been found.
8. Inspect the core face for evidence of refrigerant oil with a flashlight. On R-134a systems, the lubricant is water soluble, so no evidence of oil is likely, even with a leak.