Perfectly fine before service, warm after: valve left half-closed
The aircon cooled fine before the service visit. Two days later it blew warm air. The servicing company came back and suggested the compressor might be failing. But the timing pointed somewhere else, and the fault turned out to need no parts at all.
By Team Snowflake | Reviewed 26 Feb 2026
Case summary
Daikin Wall-mounted10 years oldHDBBedok, Singapore
- Concern
- The homeowner feared the service had damaged the compressor and a costly repair would follow
- Found
- Service valve left partially closed after routine service
- Key check
- Checked service valve positions first, then traced the cooling circuit
- Result
- Cold air returned within minutes. The unit reached its set temperature on the same visit, and no compressor work was needed.
What we were told
The aircon worked fine until the service two days earlier. Now it blew air, but the air was warm. The servicing company came back and said the compressor might be failing. The homeowner pushed back, because the unit had cooled well right up until that visit.
What we checked
When cooling fails within days of a service, the work just done is the first thing to check, not the compressor. We started at the outdoor service valves and traced the cooling circuit from there.
The compressor ran steadily, with no overheating and no abnormal cycling. It was not failing.
A quick gas reading looked close to normal, which is why the earlier check missed the fault.
The outdoor service valve sat about a quarter-turn short of fully open, restricting refrigerant flow.
The indoor coil stayed warm even with the compressor running, pointing to a flow restriction, not a dead compressor.
The reading at the outdoor unit read low, matching a restricted valve rather than a refrigerant shortage.
What we found
During the service, the outdoor valve was closed to isolate the refrigerant circuit for checks. When the work finished, the valve was turned back but not all the way. It sat about a quarter-turn short of fully open. That gap squeezed the flow of refrigerant through the system. Enough still passed for the compressor to keep running without tripping, so a quick gauge check looked acceptable. But the reduced flow starved the indoor coil, and a starved coil cannot pull enough heat from the room. The compressor ran at full power and the fan blew hard, yet the air came out warm.
What fixed it
We opened the service valve fully and watched the cooling response at the indoor coil. Cold air returned within minutes, confirming flow was restored. We then checked the other valves and service connections to make sure nothing else had been left loose or part-closed. The unit ran steadily under load. No parts were needed, no refrigerant was lost, and the compressor needed no further work.
Outcome
Cold air returned within minutes. The unit reached its set temperature on the same visit, and no compressor work was needed.
What this case teaches us
Warm air right after a service often means a step was left undone
- A service valve left a quarter-turn short can starve the coil and mimic a failing compressor. Always check it before agreeing to a costly part.
- The timing is the strongest clue. A unit that cooled fine until the day it was serviced rarely has a sudden internal failure.
- Tell the next technician the exact service date and what was done. That separates a workmanship slip from a genuine new fault.
Related reading
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