Refrigerant boils at low temperature (around -15°F at atmosphere). 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. Makes the defrost work better
Will have a thermometer either taped to the outlet line or inserted in fins.
Similar to condenser but designed for low temperatures. Fins are closely spaced for maximum surface area in compact space.
Cold refrigerant enters from TXV. Suction line (low side) carries vapor back to compressor. Make sure connections are correct. Not all TXVs have different size line fittings. The outlet of the evaporator is always closest to the power element of the TXV.
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. Clogged drain can cause freeze-up or a wet operator.
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 | Restricted airflow, failed TXV or MCC | 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 |
| Water in cab | Clogged condensate drain | Clean drain(s) and potentially modify drain valves |
Evaporator freeze occurs when surface temperature drops below 32°F. This can happen from MCC thermoter problems, restricted airflow, or failed expansion device. Ice blocks airflow and reduces cooling efficiency.