Carrier 69NT40-541-505, Operation And Service Manual

Page: 111 / 143

7–19 T-368
7.18 VALVE OVERRIDE CONTROLS
Cd41 is a configurable function code that allows man-
ual operation of the SMV valve for troubleshooting.
Test sequences are provided in Table 7–1 .
PCnt (% Setting − SMV Capacity Modulation) allows
opening of the SMV to various percentages.
The Override Timer (tIM) selection is provided to enter
a time period of up to five minutes, during which the
override is active. If the timer is active, the valve over-
ride selection will take place immediately. If the timer is
not active, changes will not take place for a few sec-
onds after the timer is started. When the timer times
out, override function is automatically terminated and
the valve returns to normal machinery control. To oper-
ate the override, do the following:
a. Press the CODE SELECT key then press an
ARROW key until Cd41 is displayed in the left
window. The right window will display a control-
ler communications code.
b. Press the ENTER key. The left display will show
a test name alternating with the test setting or
time remaining. Use an ARROW key to scroll to
the desired test. Press the ENTER key and
SELCt will appear in the left display.
c. Use an ARROW key to scroll to the desired set-
ting, and then press the ENTER key. Selections
are provided in the following table.
d. If the timer is not operating, follow the above
procedure to display the timer. Use an ARROW
key to scroll to the desired time interval and
press ENTER to start the timer.
e. The above described sequence may be
repeated during the timer cycle to change to
another override.
7.18.1 Checking the Stepper Valve
a. Checking with ohmmeter
Stop the unit, disconnect the 4-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 con-
nections and replace the motor. If near normal or nor-
mal reading occurs, proceed to step 7.18.2 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 that will open and close the SMV, allow-
ing a more thorough check of the motor.
1. Stop the unit, disconnect the 4-pin connector
from the stepper module to the valve (see Fig-
ure 7.24 ) and attach the SMA-12 stepper drive
to the connector 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 a poor connection or an open
coil. Repair or replace as required to achieve
proper operation.
3. Restart unit, set the step rate to 200PPS 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 7.18.1), and
check connections for proper continuity and
retest. If the valve is functioning, and all connec-
tions and motor resistance are good, check the
drive module (refer to step 7.18.2).
5. If the valve is determined to be faulty after com-
pleting the above steps, perform a low side
pump down. Remove valve powerhead assem-
bly, and replace with a NEW valve powerhead
assembly, torque nut to 35ft-lb, evacuate low
side, and open all service valves.
CAUTION
!
DO NOT disassemble piston from NEW suc-
tion modulating valve powerhead assembly.
Doing so may result in damage to piston.
Table 7–1 Valve Override Control Displays
Left Display Controller Communications Codes
(Right Display)
Setting Codes (Right Display)
Cd 41/SELCt tIM
(Override Timer)
0 00 (0 minutes/0 Seconds)
In 30 second increments to
5 00 (5 minutes/ 0 seconds)
PCnt
(% Setting − SMV Capacity Modulation)
AUtO
(Normal Machinery Control)
0
3
6
10
25
50
100
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