Cassette not cooling: stuck gas-flow valve, not compressor

The cassette unit pushed air but the air stayed warm. Warm air from a running unit puts the compressor first in most minds. We checked gas flow first, and the fault sat at the expansion valve, the part that meters gas into the indoor coil.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Daikin Cassette9 years oldIndustrialPioneer, Singapore

Concern: A full compressor replacement was on the table. That is several times the cost of a valve swap.
Found: Gas-flow valve stuck partly closed, restricting cooling to the indoor coil
Key check: Checked whether gas was reaching the indoor coil before blaming the compressor
Result: Full cooling came back after the valve replacement. The compressor was confirmed healthy and kept in place. A valve swap costs a fraction of a compressor replacement, and the owner kept a working part instead of paying to replace it.

What we were told

The aircon in the factory office stopped cooling about a week ago. The fan still runs, but the air coming out is warm. It had been looked at once already, and nothing about the fault had changed since. The owner wanted a second opinion before paying for a compressor.

What we checked

We first checked whether the compressor was moving gas at all, then whether enough gas was actually reaching the indoor coil. That order matters. A healthy compressor can still blow warm air if a small flow-control part downstream is stuck. Blaming the compressor first risks replacing an expensive part that works, while the cheap part that failed goes untouched.

The compressor was running normally and moving gas, which did not match the failing-compressor story.
Gas flow into the indoor coil was restricted, so the coil was being starved despite a working compressor.
The gas-flow valve, the part that meters gas into the coil, was stuck partly closed.
The control board was still sending the open command, so the valve was the fault, not the electronics telling it what to do.

What we found

The gas-flow valve had seized in a partly closed position. Only a small amount of gas could pass through, so the indoor coil never got enough to absorb heat from the room. The compressor itself was healthy. The whole problem was the one stuck valve sitting between it and the coil.

What fixed it

Nothing in the readings pointed at the compressor, so it did not need replacing. The fix was much smaller: swap out the stuck gas-flow valve, recharge the gas, and test the system end to end. Once the new valve was fitted, gas flowed freely to the coil and the indoor unit cooled within minutes.

Outcome

Full cooling came back after the valve replacement. The compressor was confirmed healthy and kept in place. A valve swap costs a fraction of a compressor replacement, and the owner kept a working part instead of paying to replace it.

What this case teaches us

Warm air does not always mean a failed compressor

A running compressor can still leave a room warm if a stuck valve blocks gas from reaching the indoor coil. The fan and the noise can sound completely normal.
The expansion valve meters how much gas flows into the coil. When it seizes partly closed, the coil starves and cannot pull heat from the room, even though the compressor is fine.
Before approving a compressor replacement, ask whether gas flow to the indoor coil was tested. That one check separates a small valve repair from a major rebuild.

Questions this case answers

Aircon fan running but the air stays warm: what does that mean?

Heat is not being absorbed at the indoor coil, and that can happen with a healthy compressor. In this Pioneer factory office the compressor ran and moved gas normally. The expansion valve, which meters refrigerant into the coil, had seized partly closed. Only a trickle got through, so the coil starved and the air came out warm.

Can a compressor be fine and the room still not cool?

Yes. The compressor sits upstream of the parts that actually feed the indoor coil. Here it sounded normal and the fan behaved normally, so nothing audible gave the fault away. Testing whether refrigerant is genuinely reaching the coil is what separates a starved coil from a failing compressor.

What does an expansion valve do, and why does it stop a cassette cooling?

It controls how much refrigerant flows into the indoor coil. Seized partly closed, it lets through too little for the coil to pull heat out of the room. On this cassette the control board was still sending the open command, so the electronics were doing their job. The valve itself had jammed.

Before approving a compressor replacement, what should I ask?

Ask whether gas flow to the indoor coil was tested and what the reading showed. That one question separates a valve swap from a major rebuild. On this unit the valve was replaced, the system recharged, and cooling returned within minutes with the original compressor left in place.

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