Chiller AC running but barely cooling — what's wrong?
We're on district cooling and the AC runs constantly but the apartment stays warm — nothing like the cooling we had last year. Airflow seems okay, it's just not cold. What could cause a chiller system to run but not cool?
3 answers
Chilled-water systems fail differently to splits. Check in this order:
- FCU filter and coil. A clogged filter or dirty coil chokes cooling. Clean the filter first — it's the most common cause.
- Chilled-water control valve. Each FCU has a valve that lets chilled water through the coil on demand. If it's stuck closed or the actuator failed, the fan blows but the coil never gets cold water. Needs a technician.
- Air in the coil / low flow. Trapped air or a strainer blockage reduces flow; a tech can bleed and check it.
- Building-side supply. If neighbours are also warm, the district-cooling supply temperature or a plant issue is to blame — that's the provider's job.
If only your flat is warm, it's your FCU (points 1–3). If the whole tower is, it's point 4.
Ours turned out to be a failed valve actuator on one FCU — fan running, no chilled water getting through. Quick swap once it was diagnosed.
If you want to move from 'it's barely cooling' to actually knowing WHY, there's a newer thread on reading a chiller's delta-T and approach temperature — the two numbers that reveal whether the plant (or your FCU) is genuinely performing or quietly fouled/starved. Worth a read if the cooling's weak but nothing's obviously 'broken' — the numbers usually point straight at the cause.
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