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The MBB controls the superheat leaving cooler to approxi-
mately 9.0° F (5.0° 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. During
initial start-up, the EXV is fully closed. After initialization peri-
od, 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 control-
ling 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.
EXV TROUBLESHOOTING PROCEDURE — Follow the
steps below to diagnose and correct EXV problems. Check
EXV motor operation first. Switch the Enable/Off/Remote
(EOR) Contact switch to the Off position. Press
the scrolling marquee until the highest operating level is dis-
played. Use the arrow keys to select the Service Test mode and
press
. The display will be TEST. Use the arrow keys
ENTER
until display shows QUIC. Press
may be required) and use
The Quick Test sub-mode is now enabled. Move the arrow
down to the appropriate circuit EXV, Circuit A EXV % Open
(Service Test Mode
QUIC
Open (Service Test Mode
EXV % Open (Service Test Mode
press
ENTER
. The current value of 0 will be displayed.
Press
and the value will be flashing. Using the
ENTER
increase the EXV position to select 100% valve position
(hold
for quick movement) and press
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. 25 — Cutaway View of the Electronic Expansion Valve
ESCAPE
ENTER
(password entry
or
to change OFF to ON.
EXV.A), Circuit B EXV %
QUIC
EXV.B), or Circuit C
QUIC
EXV.C), and
. The
ENTER
actuator should be felt moving through the EXV. Press
again twice if necessary to confirm this has occurred.
ENTER
This will attempt to force the EXV to 100% again. To close the
valve, press
ENTER
The actuator should knock when it reaches the bottom of its
stroke. If it is believed that the valve is not working properly,
continue with the following test procedure:
Check the 8-position DIP switch on the board for the proper
address. Check the EXV output signals at appropriate terminals
on the EXV module. Connect positive test lead to EXV-J2A
terminal 5 for sizes 060-190 or EXV1-J2A terminal 5 for sizes
210-300 for Circuit A. Connect lead to EXV-J2B terminal 5
for sizes 060-190 or EXV1-J2B terminal 5 for sizes 210-300
for Circuit B. Connect lead to EXV2-J2A terminal 5 for sizes
210-300 for Circuit C. Set meter to approximately 20 vdc. Us-
ing the Service Test procedure above, move the valve output
under test to 100%. DO NOT short meter leads together or pin
5 to any other pin, as board damage will occur. During the next
several seconds, carefully connect the negative test lead to pins
1,2,3 and 4 in succession. Digital voltmeters will average this
signal and display approximately 6 vdc. If the output remains
on
at a constant voltage other than 6 vdc or shows 0 volts, remove
the connector to the valve and recheck.
Press
ENTER
lem still exists, replace the EXV board. If the reading is correct,
the expansion valve and EXV wiring should be checked.
Check the EXV connector and interconnecting wiring.
1. Check color-coding and wire connections. Make sure
they are connected to the correct terminals at the EXV
board and EXV plug and that the cables are not crossed.
2. Check for continuity and tight connection at all pin
terminals.
Check the resistance of the EXV motor windings. Remove
the EXV module plug. Module plug is labeled EXV-J2A on
sizes 060-190 or EXV1-J2A on sizes 210-300 for Circuit A,
EXV-J2B for sizes 060-190 or EXV1-J2B for sizes 210-300
for Circuit B, or EXV2-J2A on sizes 210-300 for Circuit C.
50
, select 0% with
and press
and select 0% to close the valve. If a prob-
.
ENTER
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