A chiller trip is a symptom. The controller is protecting the compressor from a condition that would damage it, so resetting the alarm without finding the cause only shortens the time to the next failure. Use this guide to narrow the fault down. Refrigerant handling, electrical testing on live panels and compressor work must be left to qualified technicians.
Before anything else: read the log
Note the alarm text, then record suction and discharge pressure, water or brine inlet and outlet temperature, condenser water or ambient temperature, compressor current and oil level. Compare with the commissioning values. Nine faults out of ten are visible in those numbers, which is why a daily log is the first item in any chiller maintenance checklist.
Alarm-to-cause chart
| Alarm or symptom | Most likely causes | First checks |
|---|---|---|
| High pressure (HP) trip | Dirty condenser, fan or cooling tower fault, low condenser water flow, air in system, overcharge | Clean fins or tubes, check fans, tower, pump and strainers, compare condensing temperature with water or air temperature |
| Low pressure (LP) trip | Refrigerant leak, choked filter drier, expansion valve fault, low evaporator flow, set-point too low | Sight glass, superheat, pressure drop across drier, flow rate, brine concentration |
| Flow switch / low flow | Pump tripped, strainer choked, valve closed, air lock, undersized piping | Pump rotation and current, strainer, valves, vent air, check pressure gauges across evaporator |
| Antifreeze / low water temperature | Low flow, set-point too low, weak glycol, sensor fault | Flow, set-point, glycol strength with a refractometer, sensor calibration |
| Oil pressure / oil level | Low oil, oil diluted by liquid refrigerant, choked oil filter, failed oil heater | Oil level in sight glass, crankcase heater, oil filter differential, superheat |
| High discharge temperature | High compression ratio, low suction pressure with high superheat, failed liquid injection, valve damage | Condenser condition, superheat, injection solenoid |
| Compressor overload / motor protection | Low or unbalanced voltage, loose terminals, high head pressure, mechanical tightness | Voltage on all three phases, contactor and terminals, discharge pressure |
| Short cycling | Oversized chiller, small buffer tank, narrow differential, low flow | Tank volume, control differential, minimum load |
| Not reaching set-point | Load above capacity, dirty heat exchangers, low charge, bypassing valve, compressor not loading | Actual load vs design, approach temperatures, loading solenoids or VFD |
| Ice on suction line or compressor | Liquid floodback: expansion valve overfeeding, low load, low flow | Superheat, evaporator flow, valve bulb position |
High pressure trip
This is the most common summer fault. The condensing temperature should be roughly 10–15 °C above ambient on an air cooled chiller and about 5–8 °C above the leaving condenser water on a water cooled one. A larger gap means the condenser is not transferring heat.
- Air cooled: wash the fins from inside out with low-pressure water, check every fan runs in the right direction, and make sure hot discharge air is not being drawn back in by a wall or a neighbouring unit.
- Water cooled: check cooling tower fan and fill, water flow and strainers. If the approach is high with correct flow, the tubes are scaled and need descaling. Check water treatment afterwards or the scale will return.
- Non-condensables: if head pressure is high with a clean condenser and normal subcooling, air may have entered during service and must be purged by a technician.
The difference between the two condenser types is covered in air cooled vs water cooled chillers.
Low pressure trip
Either refrigerant is not reaching the evaporator or heat is not. Bubbles in the liquid sight glass with high superheat point to a leak or a choked drier; a noticeable temperature drop across the filter drier confirms the drier. Normal charge with low suction usually means low flow through the evaporator: a blocked strainer, a failed pump or a closed valve. On brine chillers also check concentration, because a weak mixture begins to freeze on the tubes and insulates them.
Flow and freeze alarms
Never bypass a flow switch. Without flow the evaporator can freeze and split within minutes, flooding the refrigerant circuit with water. Clean the strainer, vent air from high points, confirm the pump is delivering design flow and check that no process valve has been throttled. For sub-zero duties verify the glycol or brine strength every month; guidance on freezing points is in chilled brine temperature range.
Compressor will not start
- Control supply, emergency stop and phase-sequence relay healthy?
- Any safety still open: HP, LP, oil, flow, antifreeze, motor thermistor?
- Anti-recycle timer still counting? Most controllers enforce 3–10 minutes between starts.
- Crankcase heater on for the required period before start after a long shutdown?
- Remote start or process interlock present?
Poor cooling with no alarm
First confirm the load has not grown. A machine added to the loop, a higher throughput or a hotter season can take a chiller beyond its capacity with nothing actually wrong. Then compare approach temperatures: a rising gap between leaving water and evaporating temperature means a fouled evaporator, and a rising gap on the condenser side means a fouled condenser. Efficiency drift of this kind shows up early if you track kW per TR.
When to stop and call service
- Any repeated trip on the same safety after cleaning and flow checks
- Oil in the wrong place: on the floor, foaming, or missing from the sight glass
- Abnormal compressor noise or vibration
- Suspected refrigerant leak, or water in the refrigerant circuit
- Burnt smell, tripped breaker or damaged contactor
If your Teqtive chiller is showing a fault that this guide does not resolve, contact our service team with the model, alarm and log readings.
Frequently asked questions
Why does my chiller trip on high pressure?
The condenser is not rejecting heat. On air cooled chillers the usual causes are choked condenser fins, a failed fan, hot air recirculation or very high ambient. On water cooled chillers they are scaled condenser tubes, low cooling water flow, or a cooling tower that is not bringing the water temperature down. Air in the system and refrigerant overcharge cause the same trip.
Why does my chiller trip on low pressure?
Low suction pressure means the evaporator is starved of refrigerant or of heat. Common causes are refrigerant leakage, a choked filter drier, a faulty expansion valve, low water or brine flow, a fouled evaporator, or a set-point that is too low for the coolant in use.
Why is my chiller running but not cooling?
Check the basics first: is the set-point correct, is flow normal, and is the compressor actually loaded? After that the usual causes are a dirty condenser raising head pressure, low refrigerant charge, a heat load larger than the chiller's capacity at that temperature, or a bypass valve passing warm return water.
How often should a chiller be serviced to avoid breakdowns?
Daily log readings, monthly condenser and strainer cleaning, quarterly electrical and leak checks, and an annual shutdown service with oil analysis and tube cleaning. Chillers that run 24 hours a day should be scheduled by run hours rather than calendar months.
