AL165 - HIGH PRIORITY

Freeze Evaporating Temperature

Circuit 1's evaporator temperature is too low, risking freeze damage

Freeze Warning: Running a chiller with a frozen evaporator can cause severe damage to the heat exchanger. Allow any ice to fully thaw before attempting to restart the system.

Symptoms

Alarm code AL165 is shown for Circuit 1, often labeled as a "freeze protection" or low evaporating temperature alarm. The chiller will usually shut down Circuit 1's compressor to protect itself from freezing.
You might notice the evaporator (chiller barrel) or suction line getting frosty or icy before or during the alarm. This is a sign that the refrigerant temperature dropped too low, potentially freezing the chilled water.
The outlet water temperature may be abnormally low (close to freezing) just before the shutdown. If the chiller has temperature readouts, Circuit 1's evaporating temp or suction temperature probe (often labeled B5 on Refcool V15) will read very low.

Likely Causes

Low or No Water Flow Through the Evaporator

Inadequate water flow is the top cause for freeze alarms. If the pump isn't moving enough water, the refrigerant will over-cool the small amount of water present, causing temperatures to plummet. Clogged strainers or closed valves can drastically reduce flow and lead to this condition.

Thermostat Set Too Low

If someone set the chiller's temperature setpoint too low (colder than the design, e.g. trying to chill below ~5 °C without anti-freeze), the chiller might hit the freeze threshold. The controller triggers AL165 to prevent making ice.

Faulty Flow Switch or Pump Issue

If flow actually stopped (pump failed) but AL012 didn't trigger for some reason, the first alarm you get might be freeze protection because the water in the evaporator went stagnant and cold.

Refrigerant System Fault

Less commonly, a malfunction like an expansion valve stuck open could over-feed refrigerant, causing excessive cooling. However, modern units typically still rely on flow issues for freeze alarms.

Recommended Actions

Follow these steps in order to troubleshoot the AL165 alarm

Immediately Restore Proper Water Flow

Check the chilled water loop for any closed valves or blockages as these will cause low flow. Ensure the pump is running. If you find a clogged filter, clean it. Restoring flow will warm the evaporator back up with circulating water.

Allow the Evaporator to Thaw (If Iced)

If you saw frost/ice, leave the chiller off for a short time to let any ice melt in the evaporator. Do not run the chiller until the ice has dissipated, as running with a frozen evaporator can cause physical damage.

Important: Never attempt to chip or scrape ice from the evaporator as this can damage the delicate tubes.

Reset the Alarm

After correcting flow and giving time for temperatures to normalize, reset AL165 on the control panel. Press the alarm button to clear the fault (some chillers may auto-reset after a time delay once conditions are safe). Verify that the red alarm LED is off and the chiller is allowed to restart.

Check Glycol Concentration (If Applicable)

If your system uses an antifreeze solution (glycol), ensure the concentration is appropriate for the operating temperature. Inadequate glycol can lead to freezing at higher temps than expected. Adjust if necessary (consult chiller manual for correct percentages).

Monitor After Restart

Once the chiller is running again, watch the evaporator/suction temperatures. They should stay above the alarm threshold (typically a few degrees above 0 °C if water, lower if glycol is present). Also verify that flow remains steady. If you have pressure gauges or flow meters, ensure readings are within normal range.

When to Call a Technician

Professional Help Required:

If the AL165 alarm continues to trip repeatedly, even after you've confirmed good water flow and correct setpoints
Unresolved flow problems (pump running but low flow, or pump can't reach design flow rate)
If you do not have antifreeze in a low-temperature application
Any scenario where you are not confident in fully eliminating the risk of freezing

There may be an underlying issue like a refrigerant metering problem (expansion valve or control fault) causing evaporator temperatures to drop too low. A technician can test the freeze stat calibration and ensure the safety controls are functioning properly to protect your equipment.

Need Emergency Support?

Our certified technicians are available for emergency chiller repairs and freeze protection issues.