Troubleshooting; Finding The Optimum Settings - Danfoss EIM 336 Manual

Manual
Service (continued)
Group PNU Parameter
Control
3099 -
status
3100 -

Troubleshooting

Symptom
Pressure drop across the evaporator too high
Lack of subcooling ahead of expansion valve
Evaporator superheat too high
Suction pressure too low
Pressure drop across the expansion valve less than valve is
sized for
Expansion valve too small
Expansion valve block with foreign material
Evaporator wholly or partly iced up
Superheat of expansion valve too low
Liquid hammer Superheat reference set too low
in compressor
The S2 sensor not in good contact with the suction line
S2 sensor error: PNU 20002 Bad connection or damaged S2 sensor
AKS32R out of range: PNU The suction pressure is above the maximum limit or below
20005 the minimum limit

Finding the optimum settings

Details on the controller algorithm and settings
Problems with startup
Sometimes in one-to-one applications, the valve does not open
sufficiently on startup, and troublesome low pressure trips may
occur.
The force opening of valve function has been implemented in
the EIM 336 controller. After startup, this function will provide a
constant, set minimum opening degree during a set time period,
regardless of the superheat value. The setting parameters are
called Start OD% (n17) and StartUp time (n15).
Low Pressure Issue due to compressor cut in and cut out
One of the features of TEX valves is the external pressure
equalization making a direct and fast responding pressure
connection between the compressor suction line and underside of
the diaphragm in the valve. This enables the valve to open-/ close
momentarily with compressor capacity cut in and out .
The same function has been implemented into EIM 336, which is
controlled by the parameter n20, KpTo. In this function. kp factor
related directly to the suction pressure (To) with direct effect on the
requested signal to the ETS6 valve .
© Danfoss A/S (AC-MCI / sw), 2014-11
Superheat Controller EIM 336
Symbolic name Min. Max.
Control State 0
Ctrl Status 0 20000
Possible Cause
DKRCC.PS.RQ0.B7.02 /520H8832
Default Units e2 W
5 0
0
Check refrigerant ahead of expansion valve.
If the valve is placed much higher than condenser outlet,
check pressure difference.
1. Check superheat performance, the settings
SH min and SH max.
2. Check valve capacity.
3. Check that the maximum number of steps of
valve is same as parameter n37.
Check pressure drop across expansion valve. Replace with
larger valve.
Check refrigeration system capacity and compare with
expansion valve capacity. Replace with larger valve if neces-
sary.
Remove valve and examine the orifice.
De-ice evaporator
Increase the values of SH close and SH min.
Increase the value of SH min
Ensure that S2 sensor is secured on suction line. Insulate
sensor.
The controller will go to either the low or high boundary
depending on the error. The lowest value will be shown at a
short circuit. The highest value will be shown for a missing
connection. Check the temperature sensors.
The controller will go to either the low or high boundary de-
pending on the error. The highest value will be shown if the
signal is above the maximum value. The lowest value will
be shown if the signal is below the minimum value or for a
missing connection. Check the pressure range.
The default value of KpTo is set to automatic (i.e -1). If the
automatic tuning is not fulfilling the desired order, Increasing the
n20 setting to the fixed value will contribute to an improvement.
Too high n20 will produce high fluctuation in superheat regulation.
*10 Description
Current state of internal control state
machine.
Bit mappped status register. See also
appendix 2.
Remedy
15