A5 Daikin — Coil freeze protection
At a glance
- Severity
- FAULT STOP
- Domain
- air_handling_unit
- Reference standard
- UNI EN 13053, EN 378, ASHRAE 90.1
- Product / context
- Freeze-up protection
What it means
The AHU anti-freeze thermostat has tripped, indicating that the air temperature downstream of the heating/cooling coil has dropped below the safety threshold (typically +5 degrees C). This protects the water coil from freezing, which would cause pipe rupture with water leakage and major damage.
Probable causes
- Outdoor air damper stuck open with outdoor temperatures below zero
- Hot water coil not supplied (pump stopped, valve closed)
- 3-way valve of the hot coil stuck in closed position
- Anti-freeze thermostat defective or poorly positioned
- Glycol absent or at insufficient concentration in the water circuit
- Power supply interruption during winter
Where to start
Verify that the outdoor air damper is closed (or at minimum position). Check that the hot water coil is supplied (pump running, valve open). Verify hot water supply temperature to the coil (min 60 degrees C). Check circulation through the coil.
Full guided diagnosis in the app
The diagnostic tree for this fault has 5 guided steps with measurements, checks and resolutions. You'll find it in HVACIQ, one of the four IndexOS apps: free, works offline.
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