The compressor hums, but will not start (the motor protector trips cyclically).
The compressor is stopped by its built-in thermal protector tripping.
The contacts of the start relays get worn too soon or they get stuck.
The discharge pressure is too low.
The compressor hums, but will not start (the motor protector trips cyclically).
POSSIBLE CAUSES AND SOLUTIONS
» Failure of one of the power supply phases.
A phase failure can be detected by measuring the voltage of the phases at the compressor’s terminal strip. Then check the entire power supply line starting from the contactor inlet. You would probably find a blown fuse, or a pair of worn contacts of the contactor, or loose terminals
» Mains voltage lower than the tolerance limits.
Measure the voltage of each of the contactor phases. If it is under the tolerance limits or if there is a voltage imbalance among the phases, ask electricity supply company for servicing. If, on the other hand, electric mains are all right, measure the voltage of each of the phases at the terminals of the compressor while it is humming but doesn’t start. If there is a drop in voltage at the compressor terminals, this is proof that the power supply wiring between contactor and compressor is of insufficient size. Substitute this cabling for an appropriate one (larger size of wires).
» Interruption of the compressor’s electrical motor winding
A phase failure can be detected by measuring the voltage of the phases at the compressor’s terminal strip. Check the entire power supply line starting from the contactor inlet. You would probably find a fuse interruption, or a pair of worn contacts of the contactor, or loose terminals
» Compressor winding earthed. The compressor is mechanically locked.
Try insulation to earth. If it is insufficient, replace the compressor. It is useless to try to unlock the compressor by reversing the sequence of phases on the terminal strip. The compressor must be replaced.
The compressor is stopped by its built-in thermal protector tripping.
POSSIBLE CAUSES AND SOLUTIONS
» Inefficient condenser
Clean the finned pack.
» System overloaded with coolant.
Discharge the excess coolant as slowly as possible: dose the charge.
» Insufficient air flow to the condenser.
Check the efficiency of the blowers.
» Recirculation of hot air through the condenser.
A part of the air suctioned by the blowers is not fresh: rather, it is recirculation air, because the chiller is located in a small space. Place the chiller in a larger space.
» Suction pressure much higher than it should be.
Check that the expansion valve thermostatic sensor bulb is secured tightly to the piping and is adequately heat insulated.
» Defective thermal protector
First of all, check whether the peak and start currents are as prescribed by the compressor manufacturer. Also check the compressor frame temperature. The absence of overload or of an evident overheating prove that the thermal protector is inefficient. Replace it.
» Mains voltage lower than the tolerance limits
Measure the voltage of the phases at the contactor outlet; if the voltage among the phases is within the limits, make sure there isn’t a voltage drop at the compressor inlet while it runs. If there is a drop in voltage, the power supply wiring between contactor and compressor is of an insufficient size. Replace this cabling with an adequate one (larger size of wires).
» Compressor winding earthed or short-circuited.
Substitute the compressor
» Three-phase line unbalanced
Measure the voltage between the phases.
» Compressor overheating. .
Check that the compressor is adequately cooled by the blowers or by the return gas
The contacts of the start relays get worn too soon or they get stuck.
POSSIBLE CAUSES AND SOLUTIONS
» The number of hourly compressor cycles is too high.
Decrease the load and/or increase the differential of the thermostat
The compressor does not start and no humming is heard, although electrical current reaches its socket or power supply panel and the thermostat is adjusted to a lower temperature than the one in the tank.
POSSIBLE CAUSES AND SOLUTIONS
» A manual reset type protection device has tripped.
The tripping of high or low pressure switches is signalled by red alarm pilot lamps on the panel. Press the manual reset pressure switch and relay push-buttons.
» Defective operation of an automatic protection device (fuse, breaker, etc.).
Check for the integrity of the automatic protection devices.
» The bulb element of the thermostat is discharged; the circuit remains open.
Substitute the thermostat.
» The contactor will not get energized upon interruption of its coil.
The interruption is detected by checking the voltage at the ends of the coil. Replace the coil
» The compressor power supply line is interrupted.
Detach the line at its ends and check its continuity.
» Compressor winding interrupted.
Check the compressor, and replace it if needed
The discharge pressure is too high (either the thermal protector or the high pressure pressure-switch may trip).
POSSIBLE CAUSES AND SOLUTIONS
» Inefficient condenser
Clean the finned pack.
» Insufficient air flow to the condenser.
Check the efficiency of blowers.
» Recirculation of hot air onto the condenser.
A part of the air suctioned by the blowers is not fresh: rather it is recirculation air, this because the chiller is located in a small space. Place the chiller in a larger space.
» Suction pressure too high in relation to the expected evaporation pressure
Check that the thermostatic sensor bulb of the expansion valve is secured tightly to the piping and is adequately heat insulated.
» System overloaded with coolant.
Discharge with the excess coolant as slowly as possible: dose the charge.
The suction pressure is too high in relation to the expected evaporation pressure (possible tripping of the thermal protector and beats at the compressor head).
POSSIBLE CAUSES AND SOLUTIONS
» expansion valve bulb not well secured (if such a unit is fitted)
Secure the expansion valve bulb to the suction piping.
The suction pressure is too low in relation to the expected evaporation pressure (possible tripping of the low pressure pressure-switch).
POSSIBLE CAUSES AND SOLUTIONS
» Evaporator frozen because liquid pump is not working
Check the efficiency of the pump along the entire circuit: check the level of the liquid
» Insufficient charge of coolant. Liquid gas line obstructed
Integrate the system charge. Check the efficiency of the components mounted on the liquid gas line and the dewatering filter, in particular. If this is partially clogged, its outlet coupling will be colder than its inlet coupling
» Excessive drop in pressure in the suction line
Measure the drop in pressure of the line.
The discharge pressure is too low.
POSSIBLE CAUSES AND SOLUTIONS
» Condenser cooling air temperature too low.
This is taken care of automatically by the blower pressure switch (in models equipped with it) which stops the blower. If it is not sufficient, choke the air inlet to the condenser.
» Insufficient charge of coolant.
Integrate the charge.
» Compressor worn out.
Replace the compressor.
The discharge temperature at the compressor outlet exceeds the limit as set by the compressor manufacturer (possible tripping of the thermal protector).
POSSIBLE CAUSES AND SOLUTIONS
» Evaporator frozen.
Check the efficiency of the pump along the entire circuit: check the level of the liquid
» Insufficient charge of coolant
Integrate the charge.
» Obstruction of the liquid gas line.
Check the efficiency of the components mounted on the liquid gas line and the dewatering filter, in particular. If this is partially clogged, its outlet coupling will be colder than its inlet coupling.
The discharge temperature at the compressor outlet exceeds the limit as set by the compressor manufacturer.
POSSIBLE CAUSES AND SOLUTIONS
» Inefficient condenser.
Clean the finned pack of the condenser.
» Insufficient air flow to the condenser.
Check blower efficiency.
» Recirculation of hot air through the condenser.
A part of the air suctioned by the blowers is not fresh: rather, it is recirculation air, this is because the chiller is located in a small space. Place the chiller in a larger space.
» The expansion valve bulb (when present) is not secured tightly to the suction piping.
Secure the expansion valve bulb to the suction line.
» Evaporator frozen because liquid pump is not working.
Check the efficiency of the pump along the entire circuit: check the level of the liquid.
» Insufficient charge of coolant.
Integrate the system charge.
» Obstruction of the liquid gas line.
Check the efficiency of the components mounted on the liquid gas line and the dewatering filter, in particular. If this is partially clogged, its outlet coupling will be colder than its inlet coupling. Replace it.
» Insufficient cooling of the compressor.
Check the efficiency of blowers.
» Deterioration of the isolating material on the suction line.
Reinstate the isolation.
