R-Pro › Field cases › Air conditioning
AC Cooling Fault — Electronic Expansion Valve (EEV) Failure
Likely causes
Step 1 — Identify EEV failure mode (stuck open/closed, coil detach, blockage)
Check: Normal EEV = 'click' sound on power-on + proper temperature differential at coil. Blockage = abnormally low suction + high superheat (coil starving). Stuck open = risk of liquid slug to compressor + superheat 0 or negative. Coil detachment = from vibration/install error, no click sound.
What to do: On OFF→ON, hand on EEV to feel click and vibration. Measure coil resistance (normal 40–60 Ω). Use PCB to command 0%/100% → observe suction pressure (no change = stuck). Evap frost = coil starving signal. Measure 15–30% efficiency loss.
Step 2 — Diagnosis and replacement procedure
Check: Measure coil resistance (typically 40–60 Ω, manual prevails) — infinite or 0 = coil bad. With system OFF, command 0%/100% via PCB → observe suction pressure (no change = stuck). Frosting = evaporator frost from coil starving. System efficiency loss = 15–30% (field data).
What to do: Replace: recover refrigerant → braze/disassemble flare → install new EEV → vacuum → charge by weight. Coil only damaged = swap coil alone. Blockage = suspect system contamination (moisture/acid/debris) → add filter-drier + acid cleaning. Activate EEV learning mode after replacement (per PCB manual).
EEV faults = hard to detect (intermittent + requires diagnostic tools). On system OFF/ON, hand on coil to feel vibration as first check. Blockage = inspect overall system cleanliness (compressor acid/drier color). PCB signal fault more common than EEV itself — diagnose PCB first.
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