Step 1 — Customer History

We begin by asking whether the A/C system has been recharged previously, how long it cooled properly after the recharge, whether any A/C components have already been replaced, and if refrigerant has been added more than once. A system that cooled normally after a previous recharge and gradually lost performance often indicates refrigerant loss rather than an immediate compressor performance problem.

Step 2 — Confirm Reduced Refrigerant System Capacity

Ambient temperature and humidity are measured at the vehicle location. Using refrigerant properties, manufacturer specifications, and expected condenser performance, we estimate the expected operating range before evaluating the measured system pressures.

After allowing the system to stabilize, we evaluate high-side pressure, low-side pressure, vent temperature, compression ratio, superheat, subcooling, evaporator target temperature, actual evaporator temperature, and driver/passenger vent temperatures to determine whether the system is operating with reduced refrigerant capacity.

Step 3 — Verify Refrigerant Quantity

Before repairs begin, the refrigerant is recovered and the recovered amount is compared with the manufacturer's specified refrigerant charge. This provides one of the strongest objective measurements supporting refrigerant loss.

Step 4 — Leak Localization

Once reduced refrigerant system capacity has been confirmed, the inspection shifts to locating the source of the leak. Accessible external components are inspected before concentrating on the evaporator core.

Step 5 — Electronic Leak Detector

The evaporator drain tube is checked using an electronic refrigerant leak detector. Refrigerant escaping from the evaporator housing may be carried through the condensate drain, allowing the detector to identify refrigerant leaking from inside the HVAC case.

Step 6 — UV Dye Inspection

If fluorescent dye has previously been installed in the system, the evaporator drain tube is inspected using a UV light. Traces of fluorescent dye at the drain provide additional evidence supporting an evaporator leak.

Step 7 — Endoscopic Inspection

When access allows, an endoscopic camera is inserted to visually inspect the evaporator core and surrounding housing for oil residue, fluorescent dye, corrosion, or other evidence consistent with refrigerant leakage.

Step 8 — Technician Observations

Experienced technicians may recognize the characteristic odor associated with refrigerant and compressor oil residue inside the passenger compartment. Although this observation alone does not confirm an evaporator leak, it becomes another valuable piece of supporting evidence when considered together with the measured operating data and physical inspection results.

Step 9 — Evidence Correlation

No single measurement confirms an evaporator leak. Instead, we compare customer history, system performance, pressure relationships, compression ratio, superheat, subcooling, recovered refrigerant quantity, electronic leak detector results, UV dye inspection, endoscopic inspection, and technician observations before recommending evaporator replacement.