Code +030220215- rel. 1.4 – 25.04.2007-
25
PROBLEM CAUSE SOLUTION
The condensing pressure swings
Check the controller condenser settings, giving the parameters
“blander” values (e.g. increase the proportional band or increase
the integration time). Note: the required stability involves a
variation within +/- 0.5 bar. If this is not effective or the settings
cannot be changed, adopt electronic valve control parameters for
perturbed systems (see paragraph 8.3)
The superheat swings even with the
valve set in manual control (in the
position corresponding to the
average of the working values)
Check for the causes of the swings (e.g. low refrigerant charge)
and resolve where possible. If not possible, adopt electronic valve
control parameters for perturbed systems (see paragraph 8.3).
The superheat does NOT swings
with the valve set in manual control
(in the position corresponding to the
average of the working values)
As a first approach , decrease (by 30 to 50 %) the proportional
factor. Subsequently try increasing the integration time by the
same percentage. In any case, adopt parameter settings
recommended for stable systems.
The superheat value
swings around the set
point with an
amplitude greater
than 4°C
The superheat set point is too low
Increase the superheat set point and check that the swings are
reduced or disappear. Initially set 13 °C, then gradually reduce the
set point, making sure the system does not start swinging again
and that the unit temperature reaches the control set point.
MOP protection disabled or
ineffective
Activate the MOP protection by setting the threshold to the
required saturated evaporation temperature (high evaporation
temperature limit for the compressors) and setting the MOP
integration time to a value above 0 (recommended 4 seconds). To
make the protection more reactive, decrease the MOP integration
time.
In the start-up phase
with high evaporator
temperatures, the
evaporation pressure
is high
Refrigerant charge excessive for the
system or extreme transitory
conditions at start-up
(for
showcases only).
Apply a “soft start” technique, activating the utilities one at a time
or in small groups. If this is not possible, decrease the values of th
MOP thresholds on all the utilities.
The “Valve opening at start-up”
parameter is set too low
Check the calculation in reference to the ratio between the rated
cooling capacity of the evaporator and the capacity of the valve; if
necessary lower the value (see paragraph 8.1).
The driver in pLAN or tLAN
configuration does not start control
and the valve remains closed
Check the pLAN / tLAN connections. Check that the pCO
application connected to the driver (where featured) correctly
manages the driver start signal. Check that the driver is NOT in
stand-alone mode.
The driver in stand-alone
configuration does not start control
and the valve remains closed
Check the connection of the digital input. Check that when the
control signal is sent that the input is closed correctly. Check that
the driver is in stand-alone mode.
LOP protection disabled
Set a LOP integration time greater than 0 sec.
LOP protection ineffective
Make sure that the LOP protection threshold is at the required
saturated evaporation temperature (between the rated
evaporation temperature of the unit and the corresponding
temperature at the calibration of the low pressure switch) and
decrease the value of the LOP integration time.
Solenoid blocked
Check that the solenoid opens correctly, check the electrical
connections and the operation of the relay.
Insufficient refrigerant
Check that there are no bubbles in the sight glass upstream of the
expansion valve. Check that the subcooling is suitable (greater
than 5 °C); otherwise charge the circuit.
The valve is connected incorrectly
(rotates in reverse) and is open
Check the movement of the valve by placing it in manual control
and closing or opening it completely. One complete opening must
bring a decrease in the superheat and vice-versa. If the movement
is reversed, check the electrical connections.
Stator broken or connected
incorrectly
Disconnect the stator from the valve and the cable and measure
the resistance of the windings using an ordinary tester.
The resistance of both should be around 36 ohms. Otherwise
replace the stator. Finally, check the electrical connections of the
cable to the driver (see paragraph 5.1).
In the start-up phase
the low pressure
protection is activated
(
only for units with
compressor on
board)
Valve stuck closed
Use manual control after start-up to completely open the valve. If
the superheat remains high, check the electrical connections
and/or replace the valve.
control
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