Charging; Electronic Components; Electronic Expansion Valve (Exv) (30Mp050 - Carrier AquaSnap 30MPA Series Controls, Start-Up, Operation, Service, And Troubleshooting

valve solenoid (if installed), cooler pump, EXV, and remote
alarm relay. To use the Service Test mode, the Enable/Off/Re-
mote Control switch must be in the OFF position. Use the dis-
play keys to enter the mode and display TEST. Press
twice so that OFF flashes. Enter the password if required. Use
either arrow key to change the TEST value to the ON position
and press . Move the Enable/Off/Remote Control
ENTER
switch to enable. Press
ESCAPE
the OUTS or COMP sub-mode. ENABLE/OFF/REMOTE

switch must be set to ENABLE to operate test.
NOTE: Cooler and condenser (30MPW) water flow must be
established in order to operate compressor in service test.
Test the condenser output, cooler pump, liquid line solenoid
valve (30MPA only), crankcase heater, water valve (accesso-
ry), and alarm relay by changing the item values from OFF to
ON. These discrete outputs are then turned off if there is no
keypad activity for 10 minutes. When testing compressors, the
lead compressor must be started first. All compressor outputs
can be turned on, but the control will limit the rate by staging
one compressor per minute. Minimum load valve can be tested
with the compressors on or off. The relays under the COMP
mode will stay on for 10 minutes if there is no keypad activity.
Compressors will stay on until they are turned off by the opera-
tor. The Service Test mode will remain enabled for as long as
there is one or more compressors running. All safeties are mon-
itored during this test and will turn a compressor, circuit or the
machine off if required. Any other mode or sub-mode can be
accessed, viewed, or changed during the TEST mode. The

STAT item (Run Status VIEW) will display "0" as long as
the Service mode is enabled. The TEST sub-mode value must
be changed back to OFF before the chiller can be switched to
Enable or Remote control for normal operation.
For 30MPW units, when service is required,
Charging —
recover the refrigerant from the system.
For 30MPA units when service is required, the compressor
and evaporator can be serviced by closing the factory-installed
liquid line service valve and field-installed discharge line ser-
vice valve. After the valves are closed, recover the refrigerant
from the system.

Electronic Components

CONTROL COMPONENTS — Unit uses an advanced elec-
tronic control system that normally does not require service.
For details on controls refer to Controls section.
Access to the controls is through a hinged panel. Inner pan-
els are secured in place and should not be removed unless all
power to the chiller is off.

Electronic Expansion Valve (EXV) (30MP050-

See Fig. 26 for a cutaway view of the EXV.
071 Only) —
High-pressure liquid refrigerant enters valve through the top.
As refrigerant passes through the orifice, pressure drops and re-
frigerant changes to a 2-phase condition (liquid and vapor).
The electronic expansion valve operates through an electroni-
cally controlled activation of a stepper motor. The stepper mo-
tor stays in position, unless power pulses initiate the two dis-
crete sets of motor stator windings for rotation in either direc-
tion. The direction depends on the phase relationship of the
power pulses.
As the stepper motor rotates, its motion is transferred to lin-
ear movement by a lead screw. Refrigerant flow is modulated
by either opening or closing the port. The valve includes a pos-
itive shut-off when closed.
ENTER
and the button to enter
1. Cable
2. Glass Seal
3. Motor Housing
4. Stepper Motor
5. Bearing
6. Lead Screw
7. Insert
8. Valve Piston
9. Valve Seat
10. Valve Port
Fig. 26 — Cutaway View of the Electronic
Expansion Valve (Sizes 050-071)
Table 40 shows the number of steps for the EXV. The EXV
motor moves at 150 steps per second. Commanding the valve
to either 0% or 100% will add extra steps to the move, to en-
sure the value is open or closed completely.
Table 40 — EXV Steps
UNIT SIZE 30MP
050-071
The EXV board controls the valve. Each circuit has a
thermistor located in a well in the suction manifold before the
compressor. Suction pressure as measured by the suction pres-
sure transducer is converted to a saturated suction temperature.
The thermistor measures the temperature of the superheated
gas entering the compressor and the pressure transducer deter-
mines the saturated temperature of suction gas. The difference
between the temperature of the superheated gas and the saturat-
ed suction temperature is the superheat. The EXV board
controls the position of the electronic expansion valve stepper
motor to maintain superheat set point.
The MBB controls the superheat leaving cooler to approxi-
mately 9° F (5° C). Because EXV status is communicated to
the main base board (MBB) and is controlled by the EXV
boards, it is possible to track the valve position. The unit is then
protected against loss of charge and a faulty valve. Just prior to
compressor start, the EXV will open. At low ambient tempera-
tures the EXV is closed at start up. After initialization period,
valve position is tracked by the EXV board by constantly
monitoring the amount of valve movement.
The EXV is also used to limit cooler saturated suction tem-
perature to 50 F (10 C). This makes it possible for the chiller to
start at higher cooler fluid temperatures without overloading
the compressor. This is commonly referred to as MOP (maxi-
mum operating pressure).
If it appears that the EXV module is not properly con-
trolling circuit operation to maintain correct superheat, there
are a number of checks that can be made using test functions
and initialization features built into the microprocessor control.
See the EXV Troubleshooting Procedure section to test EXVs.
41
EXV STEPS
3690