6-14T -309
6.20.1 Precheck Procedure
a. Check unit for abnormal operation.
b. Check charge. If refrigerant is low repair as required
and again check operation.
c. If sufficient capacity cannot be maintained or unit is
tripping excessively on high pressure switch (HPS)
in high ambients, check coils and clean if required.
d. If capacity or control cannot bemaintained turn unit
OFF, then back ON. This will reset the valve in the
event the controller lost communication with the
valve, and may correct the problem.
NOTE
Carefully listen to the valve. During reset, the
valve will make a ratcheting noise that may be
heard or felt as it is attempting t o close. If this
canbeheardorfelt,itindicatesthat thecontrol-
leranddrivemoduleareattemptingtoclosethe
valve, and may serveas a quick indicationthat
the drive is in working order.
e. Operationofthevalvemaybecheckedusingthecon-
troller valve override program, function code C d41.
Refer to paragraph 6.19 for valve override test in-
structions.
6.20.2 Checking The Stepper valve
a. Checking with ohmmeter
Disconnect the four pin connector to the stepper SMV.
With a reliable digital ohmmeter, check the winding
resistance.Innormalambient,thevalveshouldhave72
to 84 ohms measured on the red/green (a-b terminals)
and on t he white/black (c-d terminals) leads. If an
infinite or zero reading occurs, check connections and
replace the motor.
b. Checking with SMA-12 portablestepper drive tester
The SMA-12 portable stepper drive tester (Carrier
Transicold P/N 07-00375-00) is a battery operated
stepperdrivewhichwillopenandclosetheSMV,which
allows a more thorough check of the operating
mechanism.
To check operation:
1. Stoptheunit,disconnectthefourpinconnectorfrom
thesteppermoduletothevalve(see
Figure 6-17)and
attachtheSMA-12stepperdrivetotheconnectorgo-
ingtothevalve.
2. Setthe SMA-12pulsepersecond (PPS)to onePPS
and either open or close valve. Each LED should
lightsequentiallyuntilallfourarelit.AnyLEDfail-
ing tolight indicatesan openon thatleg whichindi-
catesapoorconnectionoranopencoil.Repairorre-
place as required to achieve proper operation.
CAUTION
The scroll compressor achieves low suction
pressure very quickly. Do not operate the
compr essorinadeepvacuum, internaldam-
age will result.
3. Restartunit, setthesteprateto200PPS onSMA-12
forthevalve,andclosesteppervalvewhilewatching
the suction gauge. Within one minute the suction
pressurewillgointoavacuum.Thisis anindication
that the valve is moving.
4. If no change in suction pressure is detected, check
for resistance (refer to step 6.20.2), and check con-
nectionsforpropercontinuityandretest.Ifthevalve
is functioning and all connections and motor resist-
ance are good, check the controller and expansion
module.
CAUTION
DONOTdisassemblepistonfromNEWsuc-
tion modul ating valve powerhead assembly.
Doing so may result in damage to p i ston.
5. If the valve is determined asfaulty aftercompleting
theabovesteps,performalowsidepumpdown.Re-
movevalvepowerheadassembly, andreplacewitha
NEWvalvepowerheadassembly,torquenutto35ft-
lb, evacuate low side, and open all service valves.
6.21 CONTROLLER AND EXPANSION MODULE
6.21.1 Handling Modules
CAUTION
Do not remove wire harnesses from module
unless you are grounded to the unit frame
with a static safe wrist strap.
CAUTION
Unplug all module connectors before per-
forming arc welding on any part of the con-
tainer.
The guidelines and cautions provided herein should be
followed when handling the modules. These
precautions and procedures should be implemented
when replacing a module, when doing any arc welding
on the unit, or when service to the refrigeration unit
requires handling and removal of a module.
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