Step 5 - Check Operation Of The Exv; Alarms And Alerts - Carrier 30GTN Service And Troubleshooting Manual

3. Make sure that thermistor leads are connected to the proper
pin terminals at the J5 terminal strip on EXV board and
that thermistor probes are located in proper position in
the refrigerant circuit.
When these checks have been completed, the actual op-
eration of the EXV can be checked by using the procedures
outlined in Step 5 — Check Operation of the EXV section
below.
STEP 5 — CHECK OPERATION OF THE EXV — Use the
following procedure to check the actual operation of the EXVs.
The ENABLE/OFF/REMOTE contact switch must be in the
OFF position.
1. Close the liquid line service valve for the circuit to be
checked and run through the appropriate service test to
pump down the low side of the system. Run lead com-
pressor for at least 30 seconds to ensure all refrigerant
has been pumped from the low side and that the EXV has
been driven fully open (1500 steps).
NOTE: Do not use the Emergency ON-OFF switch to re-
cycle the control during this step.
2. Turn off the compressor circuit breaker(s) and the control
circuit power and then turn the Emergency ON/OFF switch
to the OFF position. Close compressor service valves and
remove any remaining refrigerant from the low side of
the system.
3. Remove screws holding top cover of EXV. Carefully re-
move top cover, using caution to avoid damage to the O-ring
seal and motor leads. If EXV plug was disconnected dur-
ing this process, reconnect it after the cover is removed.
4. Note position of lead screw (see Fig. 14). If valve has
responded properly to processor signals in Step 5.1 above,
the valve should be fully open and the lead screw should
protrude approximately
the motor.
5. Recycle the control by turning the control circuit power
on and switching the Emergency ON-OFF switch to the
ON position. This puts the control in initialization mode.
During the first 60 seconds of the initialization mode, each
valve is driven to the fully closed position (1500 steps)
by the processor. With the cover lifted off the EXV valve
body, observe the operation of the valve motor and lead
screw. The motor should turn in the counterclockwise (CCW)
direction and the lead screw should move down into the
motor hub until the valve is fully closed. Lead screw move-
ment should be smooth and uniform from the fully open
to the fully closed position.
6. When test has been completed, carefully reassemble
expansion valve. Be careful not to damage motor or
O-ring when reassembling valve. Open compressor serv-
ice valves and close compressor circuit breakers. Open
1 ⁄ in. to 3 ⁄ in. above the top of
4 4
liquid line service valve. Turn the ENABLE/OFF/REMOTE
contact switch and allow unit to operate. Verify proper
operation of unit.
This process of opening and closing the EXV (EXV.A/
EXV.B under OUTS) can be repeated by using these Service
Test steps and recycling the control as described in the pre-
ceding steps. If the valve does not operate as described when
properly connected to the processor and receiving the cor-
rect signals, it should be replaced.
If operating problems persist after reassembly, they may
be due to out-of-calibration thermistor(s) or intermittent con-
nections between the EXV board terminals and the EXV plug.
Recheck all wiring connections and voltage signals.
Other possible causes of improper refrigerant flow con-
trol could be restrictions in the liquid line. Check for plugged
filter drier(s), restricted metering slots in the EXV, or par-
tially closed liquid line service valves. Formation of ice or
frost on the lower body of the EXV is one symptom of re-
stricted metering slots. Clean or replace the valve if neces-
sary. Wrap a wet cloth around the valve if it is to be replaced
to prevent the heat from damaging the internal components
of the valve.
NOTE: Frosting of the valve is normal during service test
and at initial start-up. The frost should dissipate after 5 to
10 minutes operation of a system that is operating properly.
NOTE: The EXV orifice is a screw-in type and may be re-
moved for inspection and cleaning. Once the top cover has
been removed, the EXV motor may be taken out by remov-
ing the 2 cap screws securing motor to valve body. Pull mo-
tor, lead screw, and the slide assembly up off the orifice as-
sembly. See Fig. 14. A slot has been cut in top of orifice
assembly to facilitate removal using a large screwdriver. Turn
orifice assembly counterclockwise to remove.
When cleaning or reinstalling orifice assembly, be careful
not to damage orifice assembly seals. The bottom seal acts
as a liquid shut-off, replacing a liquid line solenoid valve.
Reassembly of valve is made easier by screwing the slide
and lead screw assembly out of the motor. Align hole in top
of slide with the guide pin in orifice assembly and gently
push slide and lead screw onto orifice assembly about half-
way. Screw motor onto lead screw and secure EXV motor
with cap screws. Be careful not to twist or pull on wires from
EXV motor to valve cover pin connections. Check EXV op-
eration in quick step steps.
Alarms and Alerts —
or fault conditions, and may cause either one circuit or the
whole unit to shut down. They are assigned code numbers as
described in Table 27.
47
These are warnings of abnormal