Aircon Cassette Warm, Stuck Expansion Valve

Case Details

What We Checked

• Compressor was running and discharge pressure was within normal range — the compressor was pumping correctly.
• Suction pressure was lower than expected at the indoor coil — indicating restricted refrigerant flow on the inlet side.
• Superheat at the indoor coil was excessively high — the coil was starved of refrigerant.
• Electronic expansion valve was stuck in a partially closed position — confirmed by the pressure differential across it.

The Diagnosis

The electronic expansion valve had seized in a partly closed position due to internal contamination on the valve needle seat. Only a fraction of the normal refrigerant flow was reaching the indoor coil. With less refrigerant absorbing heat, the coil surface temperature stayed well above the room air temperature, so the output felt warm even though air was moving. The compressor was working correctly the whole time — discharge pressure confirmed it was pumping at full capacity. But it was pushing refrigerant against the bottleneck created by the stuck valve, which is why suction pressure dropped abnormally low. The symptom looked like compressor weakness because the end result was the same: warm air. The difference shows up in the pressure readings.

What Fixed It

We explained the findings and presented two paths. The first option was to replace the expansion valve — a targeted repair that restores refrigerant flow without touching the compressor. The second was the compressor replacement the previous contractor had quoted, which was unnecessary since the compressor tested healthy. We recommended the valve replacement because the diagnostic data confirmed the compressor was not the problem. After swapping the valve, we recharged the system, verified that suction and discharge pressures returned to normal range, and confirmed that superheat at the indoor coil dropped to the correct operating value. The coil temperature fell within minutes.

Full cooling was restored after the valve replacement. The compressor was confirmed healthy and retained. The repair cost a fraction of the compressor replacement quote.

Why This Happens

Cassette not cooling — expansion valve vs. compressor failure.

• The expansion valve controls how much refrigerant enters the indoor coil. If it sticks partly closed, flow drops and the coil cannot absorb enough heat. The air blows but stays warm because there is not enough cold refrigerant surface to cool it.
• Superheat readings at the indoor coil show whether it is getting enough refrigerant. High superheat with a running compressor points to a restriction upstream. Ask your technician whether they measured superheat before diagnosing compressor failure.
• A stuck expansion valve is a smaller repair that restores flow without touching the compressor. The cost difference between an expansion valve swap and a compressor replacement can be several times over, which is why the diagnosis step matters so much.
• Electronic expansion valves seize from internal contamination, coil winding burnout, or corrosion on the valve needle seat. In commercial units that run long hours in dusty environments, the valve sees more wear than in a residential setting.