Fault Library

Rack discharge pressure trips high-pressure safeties or runs abnormally high, causing compressors to cut out.

Suction pressure at the rack runs below the target suction group setpoint, starving cases and pulling compressors down.

One or more rack compressors start and stop rapidly, causing wear, oil loss, and poor temperature control.

A rack compressor is commanded on by the controller but does not run.

Compressor motor overload / internal protector trips on high amperage.

Compressor trips on oil-pressure differential safety or oil-level control on a parallel rack.

Liquid refrigerant returns to the compressor crankcase, diluting oil and risking valve/bearing damage.

Expansion valve underfeeds the evaporator, giving high superheat and a warm case.

Expansion valve overfeeds the evaporator, giving low superheat and risking floodback.

System is undercharged, producing flash gas, low suction, and warm cases.

Air or other non-condensable gases raise head pressure and condensing temperature.

One or more condenser fans (EC or contactor-driven) fail to run, raising head pressure.

Airflow restriction across the condenser raises condensing temperature and head pressure.

Ice builds on an evaporator coil, blocking airflow and warming the case.

An evaporator/case fan motor overheats and its internal Klixon thermal cut-out opens, stopping the fan and warming the case until the motor cools and resets.

Condensate can't drain because the drain line or pan freezes, so water backs up, re-freezes on the coil, and overflows or ices the case floor.

The metering valve oscillates instead of holding steady superheat, so suction pressure and case temperature swing and capacity suffers.

Ice builds on the fan blades and shroud, unbalancing the fan — airflow drops, the case warms, and the motor runs loud and hot.

A case is not completing defrost, leading to progressive ice accumulation.

A display case or walk-in runs above its product temperature target.

A failed transducer or temperature sensor feeds the rack controller bad data, causing erratic control.

Loss of a phase or low supply voltage trips compressors and condenser fans across the rack.

Liquid receiver level outside the design band affects liquid feed and head-pressure control.

On a transcritical CO2 rack the high side runs above the optimum gas-cooler pressure target, hurting efficiency and risking high-pressure trips or relief-valve discharge (relief settings are system-specific — see the unit nameplate).

The intermediate flash-tank/receiver pressure drifts off target because the flash gas bypass (FGB) valve isn't controlling correctly, upsetting liquid feed to the cases.

With the rack off, warming CO2 raises system pressure toward the relief setting; the standstill unit must hold pressure down or refrigerant is lost.

On a booster rack the LT compressors discharge into the MT suction; a staging or capacity problem on either stage upsets both temperature levels.

Failed gas-cooler fans or a dirty gas-cooler coil raise the outlet temperature and force higher, less efficient transcritical pressure.

Moisture in a CO2 system, or letting pressure fall below the triple point (75.1 psia ≈ 60 psig / -69.8°F), can form ice or solid dry ice and block metering devices.

Oil (PAG/POE for CO2) fails to return or manage correctly across the booster rack, tripping oil safeties.

The parallel compressor pulls flash gas directly from the receiver in warm ambient to boost efficiency. When it won't run or stage, flash gas dumps through the FGB valve to MT suction and efficiency (and MT capacity) suffer.

On ejector-equipped racks the multi-ejector block recovers high-side pressure energy to lift MT suction gas into the receiver, cutting compressor work. A stuck cartridge or control fault kills the efficiency gain and upsets receiver control.

CO2 compressors run high discharge temperatures because of the high pressure ratio; if discharge-temp control (liquid/vapor injection or interstage desuperheat) fails, the compressor trips or is damaged.

Medium-temp suction pressure runs above target, warming MT cases and forcing the LT stage to work against a high interstage. Often a staging, flash-gas, or false-load problem rather than a compressor fault.

A CO2 gas-detection alarm in the plant room or sales area signals a leak. CO2 is heavier than air, colorless, and odorless — rising ppm is an asphyxiation risk and must be treated as a safety event, not just a refrigerant loss.

CO2 control leans heavily on accurate high-side, receiver, and suction transducers. A drifting or failed transducer makes the controller drive valves and compressors to the wrong targets, mimicking many other faults.

Bringing a CO2 rack online (after service, power loss, or commissioning) has strict pressure rules. Doing it out of order risks dry-ice blockage, relief loss, or nuisance trips.

A plug-in / self-contained display case running on R-290 (propane) isn't holding temperature. These are sealed hermetic systems with a tiny charge, so most no-cool calls are airflow, condenser, or electrical — not a charge problem.

R-290 is propane — an A3 flammable refrigerant. Even the small charge in a self-contained case can create a flammable atmosphere near the unit. Handle any leak or sealed-system repair as a fire/ignition hazard first.

The evaporator in a self-contained R-290 case is frosted/iced, blocking airflow so the case slowly warms. Usually a defrost, drain, or airflow issue on the sealed unit.

The hermetic compressor in a self-contained R-290 case won't start or trips. Often a start component, overload, or controller issue rather than the sealed system.

The condenser fan on a self-contained R-290 case has stopped or slowed, so head pressure climbs, the compressor overheats/trips, and the case warms. On plug-ins this is one of the most common no-cool causes — usually a failed EC/PSC fan motor, seized bearing, or blocked coil.

The electronic case controller (e.g. Dixell, Carel, Danfoss on plug-in R-290 cases) is misconfigured, alarming, or reading a bad sensor — so the case won't cool right even though the sealed system and fans are fine. Setpoint, defrost, and probe faults dominate here.

Indoor and outdoor units lose serial communication and stop or flash a comm error (e.g. Daikin U4/UF, Mitsubishi E6/6607, LG CH04).

VRF systems are charge-critical; a small shortage or leak drops capacity and can trigger low-pressure or refrigerant-shortage codes.

A stuck, miswired or failed indoor/outdoor EEV makes one zone over- or under-feed — hunting temps, floodback, or starving.

The outdoor unit trips on high pressure — usually airflow, overcharge or a blocked circuit — protecting the inverter compressor.

The inverter PCB trips on overcurrent, DC-bus or IPM temperature, protecting the variable-speed compressor and drive.

On a 2-pipe heat-pump VRF, one zone calls for heating while another calls for cooling — it can only do one, so a zone is locked into standby.

A failed inverter-driven outdoor fan motor drives high head in cooling (or low capacity in heating) and often throws a fan/position error.

The glycol circulator runs but delivers little or no flow — the loop starves and downstream coils/chillers lose capacity or trip on flow.

The pump cavitates when suction pressure drops below what the fluid needs — vapour bubbles collapse in the impeller, causing gravel-like noise, vibration and erosion.

Air trapped at the pump or a low-pressure loop lets the impeller spin in vapour instead of liquid, so it stops moving fluid.

A weeping mechanical seal or packing loses glycol, drops loop pressure and forces constant makeup that dilutes the mix.

The pump motor draws high current and trips its overload/VFD — usually viscosity, mechanical drag, or an electrical/drive fault.

Too little glycol risks freeze/burst; too much needlessly raises viscosity — cutting flow and heat transfer and overworking the pump.

The chiller trips on low chilled- or condenser-water flow — the most common chiller nuisance trip.

Low refrigerant (evaporator) temperature trips the freeze protection to stop the barrel freezing and splitting.

High condensing pressure trips the chiller or drops capacity — airflow (air-cooled) or condenser water/tower (water-cooled) driven.

A leak or undercharge drops evaporator pressure and capacity and can trip the freeze/low-pressure safety.

Loss of net oil pressure trips the compressor safety on screw/scroll chillers, protecting bearings and rotors.

The compressor draws high or imbalanced current and trips the overload / motor protector.

A centrifugal compressor surges (flow reversal) at high lift or low load — a repeating whoosh/rumble with swinging amps that damages bearings if left.

A rising evaporator or condenser approach means the heat exchanger isn't transferring well — usually fouling/scale or charge — quietly costing efficiency.

Cold-water temp stays too far above the wet-bulb — the tower isn't rejecting design heat, pushing up condenser head and chiller kW.

Fan, motor, belt or gearbox problems cut airflow (raising approach) and often show as vibration, noise or a VFD trip.

Loss of water-treatment control causes scale/fouling (poor performance), corrosion, and dangerous biological growth (Legionella).

Scale, debris or collapsed fill media reduce wetted surface and airflow — the tower loses capacity and approach climbs.

Makeup usage is higher than expected — from overflow, excess drift, over-bleed, or leaks — wasting water and chemicals.

Basin level too low (pump cavitation/air) or too high (overflow) from makeup-control or level-device faults.

In cold weather, ice forms on fill, louvers and structure — damaging the tower and blocking airflow if capacity/heat/flow aren't managed.