Afternoon cutouts traced to blocked outdoor airflow
Aircon case in Ang Mo Kio, Singapore: airflow traced to outdoor unit in a blocked alcove with new installation above trapping discharge airflow — thermal protection tripping during peak afternoon heat after targeted diagnosis checks.
Case details
What client reported
The customer said the unit cut out every day between 2pm and 4pm for about a month. It restarted on its own after an hour or so. Mornings were fine. A previous technician had suggested the compressor might be failing but had not done any testing. The timing matched when a new water heater platform had been installed nearby.
What we found
We visited in the afternoon to observe the outdoor unit during the cutout window, not in the morning when the problem was absent
- Outdoor unit in a partly enclosed utility alcove — three sides enclosed, open at the front
- New water heater platform installed above the outdoor unit six weeks earlier — its base sat 20cm above the top discharge grille, blocking the hot air exhaust
- Discharge air temperature measured — significantly above ambient. Hot air was cycling back down from the platform instead of dispersing upward.
- Compressor surface temperature measured — elevated but within the range expected for thermal protection tripping, not internal damage
The water heater platform was trapping hot discharge air in the alcove. During peak afternoon heat, this pushed the compressor's thermal switch to trip every day. The compressor was not damaged. It was shutting down to protect itself.
What we did
We discussed options with the customer. The platform could be modified to let discharge air through, or a duct could direct the air out of the alcove. The customer agreed to raise the platform by 40cm. After the change, the outdoor unit ran through two consecutive afternoons without cutting out.
The afternoon cutouts stopped once the platform clearance was increased. No parts were needed and the compressor was not damaged. The customer was told to keep at least 50cm of clear space above the discharge grille and to check before placing anything near the outdoor unit in future.
Timeline
Day 1
Afternoon cutout pattern reported — unit working in morning, tripping around 2–4pm, restarting after an hour
Day 1
Visited during an afternoon cutout — outdoor unit surface temperature was high. A new structure above it was trapping hot discharge air.
Day 1
Afternoon inspection confirmed blocked outdoor airflow from new platform, obstruction modified, subsequent afternoons ran without cutout
What we learned
Time-of-day cutouts and outdoor unit airflow.
- The compressor's thermal switch trips when the casing gets too hot. Trapped discharge air nearby makes this happen sooner.
- Any new structure placed above or around the outdoor unit can block airflow. This can cause afternoon trips that never happened before.
- A unit that cuts out only in the afternoon almost always has an outdoor unit heat problem. An internal compressor fault is unlikely.
- The compressor is usually undamaged. It trips to protect itself and resets once cooled. This is why the unit restarts on its own after an hour.
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