Carel EVD4, User Manual, Page: 31 / 48

31
ENGL
ISH
EVD
4
+030220227 - rel. 2.1 - 12.06.2008
5. TROUBLESHOOTING
The following table lists a series of possible malfunctions that may occur when starting and operating the
driver and the electronic valve. These cover the most common problems and are provided with the aim
of offering an initial response for resolving the problem.
Problem Cause Solution
Liquid returns to the
compressor during the
operation of the controller
The probes measure an incorrect superheat
value Check that the pressure and the temperature measured are correct and that the position of the probes is correct.
Check the correct range of the pressure probe. Check the correct electrical connections of the probes.
The type of refrigerant set is incorrect Check and correct the parameter relating to the type of refrigerant.
The type of valve set is incorrect Check and correct the valve type parameter.
The valves are not connected correctly (rever-
sed) and are open Check the movement of the valve by setting manual control and closing and opening it completely. If reversed,
check the connections.
The superheat set point is too low Increase the superheat set point.
Low superheat protection ineffective Increase the low superheat threshold and/or decrease the low superheat integral time.
Valve blocked open Check if the superheat is low on one or more showcases, with the valve position permanently at 0. Use manual
control to close and open it completely. If the superheat is always low, check the electrical connections and/or
replace the valve.
The “Circuit/EEV ratio” parameter is too high
on many showcases and the control set point is
often reached (for showcases only) Try lowering the value of the “Circuit/EEV ratio” parameter on all the utilities, checking that there are no repercus-
sions on the control temperature.
Liquid returns to the
compressor only after
defrosting (for showcases only)
Before becoming stable, the superheat value is
very low for a few some minutes Increase the low superheat threshold to at least 2 °C higher than the (low) superheat value and/or decrease the low
superheat integral time, which must always be greater than zero.
The superheat never reaches very low values Set more reactive parameters (increase the proportional factor, increase the integral time, increase the differential
time) to bring forward the closing of the valve even when the superheat is greater than the set point.
Multiple showcases defrost at the same time Stagger the start defrost times. If this is not possible, if the conditions described in the two previous points are not
present, increase the superheat set point for the showcases involved.
The valve is greatly oversized Set the key11 parameter to 24717, valve type to 99 (custom), disable the extra steps in opening parameter and
reduce the maximum valve steps parameter to a value that is 20% higher than the maximum valve position reached
during normal control. The time taken to reach steady operation after defrosting will be longer.
Liquid returns to the
compressor only when starting
the controller (after being OFF) The “Circuit/EEV ratio” parameter is too high Lower the value of the “Circuit/EEV ratio” parameter.
The system swings
The condensing pressure swings Check that the condensing pressure is stable (m/- 0.5bar from the set point). If not, try to stabilise the
condensing pressure using the controller (e.g. disable the condensing pressure control and operate the fans at
maximum speed, depending on the operating conditions of the installation).
The superheat set point is too low Increase the superheat set point, checking that the temperature of the unit remains low and reaches the control set
point. If the situation improves, adopt this new set point, otherwise see the following points.
The superheat also swings with the driver in
manual control Observe the average operating position of the valve, enable manual positioning and set the opening of the valve to
the average value observed: if the swing persists, re-enable automatic operation and set more reactive parameters
(increase the proportional factor, increase the integral time, increase the differential time).
The superheat only swings with the driver in
automatic control Observe the average operating position of the valve, enable manual positioning and set the opening of the valve
to the average value observed: if the swing stops, re-enable automatic operation and set less reactive parameters
(decrease the proportional factor, increase the integral time).
Bubbles of air can be seen in the liquid indicator
upstream of the expansion valve or adequate
subcooling is not guaranteed Charge the circuit with refrigerant.
During start-up with high
evaporator temperature, the
evaporation pressure is high
MOP protection disabled Activate the MOP protection, setting the threshold to the required saturated evaporation temperature (high evapo-
ration temperature limit for the compressors) and the MOP integral time to a value greater than 0 (recommended
4sec).
MOP protection ineffective Make sure that the MOP threshold is at the required saturated evaporation temperature (high evaporation tempera-
ture limit for the compressors) and decrease the value of the MOP integral time.
Excessive refrigerant charge for the system (for
showcases only) Apply a “soft start” technique by activating the utilities one at a time or in small groups. If this is not possible,
decrease the values of the MOP thresholds.
During start-up the unit
switches off due to low
pressure (units with on-board
compressor only)
The “Circuit/EEV ratio” parameter is too low Increase the value of the “Circuit/EEV ratio” parameter.
The driver is not set correctly in STAND ALONE Check that the strand alone parameter is activated.
The driver digital input is not connected correctly Check the connection of the digital input.
LOP protection disabled
Activate the LOP protection by setting the threshold to the required saturated evaporation temperature (between
the operating temperature and the calibration of the low pressure switch) and the LOP integral time to a value
greater than 0 (recommended 4sec)
LOP protection ineffective Make sure that the LOP threshold is at the required saturated evaporation temperature (between the operating
temperature and the calibration of the low pressure switch) and decrease the value of the LOP integral time.
Solenoid blocked Check that the solenoid opens correctly, check the electrical connections and the operation of the relay.
Insuffi cient refrigerant Check that there are no bubbles of air in the liquid indicator upstream of the expansion valve. Check that the
subcooling is suitable (greater than 5°C). Charge the circuit.
Valve blocked closed Use manual control to close and open the valve completely. If the superheat remains high, check the electrical
connections and/or replace the valve.
The unit switches off due to low
pressure during control (units
with on-board compressor
only)
LOP protection disabled Activate the LOP protection by setting the threshold to the required saturated evaporation temperature (between
the operating temperature and the calibration of the low pressure switch) and the LOP integral time to a value
greater than 0 (recommended 4sec)
LOP protection ineffective Make sure that the LOP threshold is at the required saturated evaporation temperature (between the operating
temperature and the calibration of the low pressure switch) and decrease the value of the LOP integral time.
Solenoid blocked Check that the solenoid opens correctly, check the electrical connections and the operation of the relay.
Insuffi cient refrigerant Check that there are no bubbles of air in the liquid indicator upstream of the expansion valve. Check that the
subcooling is suitable (greater than 5 °C). Charge the circuit.
Valve blocked closed Use manual control to close and open the valve completely. If the superheat remains high, check the electrical
connections and/or replace the valve.
The showcase does not reach
the set temperature, despite the
value opening to the maximum
(for showcases only) Solenoid blocked Check that the solenoid opens correctly, check the electrical connections and the operation of the relay.
Insuffi cient refrigerant Check that there are no bubbles of air in the liquid indicator upstream of the expansion valve. Check that the
subcooling is suitable (greater than 5 °C). Charge the circuit.
Valve blocked closed Use manual control to close and open the valve completely. If the superheat remains high, check the electrical
connections and/or replace the valve.
The showcase does not reach
the set temperature, and the
position of the valve is always
to 0 (for showcases only) The driver is not set correctly in STAND ALONE Check that the strand alone parameter is activated.
The driver digital input is not connected correctly Check the connection of the digital input.