Cassette not cooling traced to stuck expansion valve, not compressor failure

What we found

We measured refrigerant pressures and superheat at the indoor coil before testing the compressor.

• 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 expansion valve had seized in a partly closed position. Only a fraction of the normal flow was reaching the indoor coil. The coil could not absorb enough heat from the room air, so the output felt warm. The compressor was working fine the whole time. It was pumping against the block caused by the valve.

What we did

We replaced the expansion valve. Flow returned to normal and the indoor coil temperature dropped to the correct range. Superheat readings confirmed proper running.

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.

What we learned

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. The coil cannot absorb enough heat, so the air blows but stays warm.
• Superheat readings at the indoor coil show whether it is getting enough refrigerant. High superheat with a running compressor points to a block upstream. That is usually the expansion valve.
• A stuck expansion valve is a smaller repair. Replacing it restores flow without touching the compressor. The compressor is a much larger and more costly part.