Carrier Streamline Scroll 69NT20-531-300 - Manual (Page 78)

6-14 T-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 be maintained 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 to close. If this
can be heard or felt, it indicates that the control-
ler and drive module are attempting to close the
valve, and may serve as a quick indication that
the drive is in working order.
e. Operation of the valve may be checked using the con-
troller valve override program, function code Cd41.
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. In normal ambient, the valve should have 72
to 84 ohms measured on the red/green (a-b terminals)
and on the white/black (c-d terminals) leads. If an
infinite or zero reading occurs, check connections and
replace the motor.
b. Checking with SMA-12 portable stepper drive tester
The SMA-12 portable stepper drive tester (Carrier
Transicold P/N 07-00375-00) is a battery operated
stepper drive which will open and close the SMV, which
allows a more thorough check of the operating
mechanism.
To check operation:
1. Stop the unit, disconnect the four pin connector from
the stepper module to the valve (see Figure 6-17 ) and
attach the SMA-12 stepper drive to the connector go-
ing to the valve.
2. Set the SMA-12 pulse per second (PPS) to one PPS
and either open or close valve. Each LED should
light sequentially until all four are lit. Any LED fail-
ing to light indicates an open on that leg which indi-
cates a poor connection or an open coil. Repair or re-
place as required to achieve proper operation.
CAUTION
The scroll compressor achieves low suction
pressure very quickly. Do not operate the
compressor in a deep vacuum, internal dam-
age will result.
3. Restart unit, set the step rate to 200 PPS on SMA-12
for the valve, and close stepper valve while watching
the suction gauge. Within one minute the suction
pressure will go into a vacuum. This is an indication
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-
nections for proper continuity and retest. If the valve
is functioning and all connections and motor resist-
ance are good, check the controller and expansion
module.
CAUTION
DO NOT disassemble piston from NEW suc-
tion modulating valve powerhead assembly.
Doing so may result in damage to piston.
5. If the valve is determined as faulty after completing
the above steps, perform a low side pump down. Re-
move valve powerhead assembly, and replace with a
NEW valve powerhead assembly, torque nut to 35 ft-
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.