Refrigerant boils at low temperature (around 32°F). Latent heat absorption from cab air causes this phase change. This is where cooling actually happens.
Cold evaporator surface causes moisture to condense out of cab air. Water drains through tube to outside of machine. Prevents fogging and improves comfort.
Located behind dash panel. Access may require removing panels or raising cab on some models. Look for insulated refrigerant lines entering box.
Similar to condenser but designed for low temperatures. Fins are closely spaced for maximum surface area in compact space.
Cold refrigerant enters from TXV/orifice tube. Suction line (low side) carries vapor back to compressor.
Collects condensate and drains to outside. Check for clogs and proper drainage. Must be clear for proper operation.
Measure temperature at duct louver with AC on full cold. Normal: 45-53°F. Below 40°F indicates possible freeze-up. Above 55°F indicates problem.
Low-side pressure should be 25-45 psi at 70-80°F ambient. Low pressure indicates low charge or restriction. High pressure indicates overcharge.
Verify water draining from condensate tube. Pour water into drain pan to check for blockages. Clogged drain can cause water damage and odor.
Look for ice formation on evaporator or suction line. Check for restricted airflow or low refrigerant charge causing freeze-up.
| Symptom | Cause | Diagnosis |
|---|---|---|
| Evaporator freeze-up | Low charge, restricted airflow, failed TXV | Ice formation, low suction pressure, cold duct temp |
| Poor cooling performance | Restricted airflow, internal contamination | Warm duct temp, normal pressures, check filters/blower |
| Refrigerant leak | Corrosion, vibration fatigue, impact damage | UV dye test, electronic leak detector, oil residue |
| Odor from vents | Mold growth in drain pan, clogged drain | |
| Water in cab | Clogged condensate drain, damaged drain pan | Water leak location, drain flow test |
Evaporator freeze occurs when surface temperature drops below 32°F. This can happen from low refrigerant charge, restricted airflow, or failed expansion device. Ice blocks airflow and reduces cooling efficiency.
Evaporator replacement is major job requiring dashboard removal on some models. Plan for extended downtime. Replace expansion device and receiver/dryer when replacing evaporator.