Checking The Stepper Valve - Carrier 69NT40--541--200 TO 299 Operation And Service

sure that the wires terminate in accordance with the
wire markings (addresses).
h. Attach a manifold gauge set. If the unit is operating in
the perishable mode, proceed to step i. I f the unit t is
operating in the frozen mode, proceed to step j.
i. Perishable operation: If the operation of the unit is
in question, place the set point to approximately 6°C
(11°F) less than the current box temperature, so the
unit goes into pulldown. Run the unit for approximate-
ly one minute. Record readings on gauges and cur-
rent draw. The current draw and pressures should go
up. Place set point to 0.5°C (0.9°F) above current box
temperature to fully modulate valve, and run for
approximately one minute.
NOTE
The unit may shut off for a short time. Wait until
the unit self starts and sufficient time has
elapsed to cause the valve to fully modulate.
Record new gauge readings and current draw. The
suction pressure should go into a vacuum and the
current draw should have gone down. If little or no
change to the suction pressure or current draw oc-
curs, this is an indication of a malfunctioning SMV.
j. Frozen operation: In frozen mode the valve will tend
to stay open as much as possible. Again, this is de-
pendent upon current limit setting and control logic.
Turn the unit OFF and ON, as in the perishable mode,
and watch the gauges. The valve will run at 21% open
if CREL logic is active, and will open to maximum al-
lowable after this. Dependent on ambient conditions,
there should be an increase in suction pressure and
current draw as the valve opens, however, this may
be difficult at times to fully determine.
k. If the unit still does not operate properly, stop unit, and
proceed to the following step to check out the SMV
system.

6.18.2 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. If near normal or normal reading occurs,
proceed to section 6.18.3 to check out the controller.
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 motor.
To check operation:
1. Stop the unit, disconnect the four pin connector from
the stepper module to the valve (see Figure 6-21)
and attach the SMA-12 stepper drive to the connec-
tor going 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 failing
to light indicates an open on that leg which indicates
T--317
a poor connection or an open coil. Repair or replace
as required to achieve proper operation.
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 6.18.2), 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 drive module. (Refer to
step 6.18.3)
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.
DO NOT disassemble piston from NEW suc-
tion modulating valve powerhead assem-
bly. Doing so may result in damage to pis-
ton.
6.18.3 Checking The Controller
a. Turn unit OFF.
b. With voltmeter set to read 20 volts DC, attach the pos-
itive lead to MC1 and the negative lead to the TP9.
Turn ON unit, and watch the volt meter. After a short
delay, the reading should remain unchanged at 0
volts. If 5 VDC, check jumper wire form MC1 to MC8
is in place, if not, install and retest.
c. Disconnect the four pin connector to the SMV.
d. With voltmeter set to read 24 volts AC, attach the pos-
itive lead to the drive module outlet pin "A" (wire 1A) of
the 4 pin connector and the negative lead to the "B"
pin (wire 1B).
e. Turn ON unit, and watch the volt meter. After a short
delay, the reading should remain unchanged at 0
volts. If 5 VDC, check jumper wire form MC1 to MC8
is in place, if not install and retest.
f. Repeat for pins "C" and "D" (wires 2 A and 2 B).
g. If only one set of pins reads a voltage, check connec-
tions and retest.
h. If the retest reads out the same, controller is faulty.
i. If no voltage is present in any step, the output from the
controller may be faulty
6.19 AUTOTRANSFORMER
If the unit does not start, check the following:
a. Make sure the 460 vac (yellow) power cable is
plugged into the receptacle (item 3, Figure 4-1) and
locked in place.
b. Make sure that circuit breakers CB-1 and CB-2 are in
the "ON" position. If the circuit breakers do not hold in,
check voltage supply.
c. There is no internal protector for this transformer
design, therefore, no checking of the internal protec-
tor is required.
6-18
CAUTION