Carrier Transicold X4 7300, Operation & Service Manual

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8.9.7 Stepper Test Harness
A stepper test harness (Carrier Transicold part number
(07 − 00515) is available for testing the compressor suc-
tion modulation valve (CSMV) and evaporator expan-
sion valve (EVXV).
Figure 8.33 Stepper Test Harness
The test harness is installed by disconnecting the
2SVM connector at the SVM module and plugging the
C1 connector (see
Figure 8.33 ) into the module and
C2 connector into the unit harness. With the test har-
ness in place, the A1/A2 test harness connectors may
be used to perform the following EVXV testing while
the B1/B2 connectors may be used to perform the
CSMV testing.
8.9.8 Compressor Suction Modulation Valve
(CSMV)
The purpose of the CSMV (see Figure 8.34 ) is to main-
tain the compressor within its operating envelope and
maximize unit capacity and fuel economy.
Figure 8.34 Suction Modulation Valve (CSMV)
[
If it is suspected that the CSMV is malfunctioning, the
most efficient method of diagnosing the valve is to run
a Pretrip (refer to
Section 3.5 ). The Pretrip steps will
check the remainder of the system and the CSMV spe-
cific test will check the valve. During the CSMV specific
test the valve will be brought to a preset position, the
unit started and then the valve will be opened while the
control system monitors suction pressure. If there is a
problem with the valve internal motor/piston assembly
or control system wiring to the valve the test will fail.
a. Diagnostics - Control System or Wiring
1. Disconnect the CSVM connector.
2. Place the STOP/RUN-OFF switch in the
START/ RUN position, DO NOT ALLOW THE
UNIT TO START. When the MessageCenter
displays “SMV CLOSING”, measure the AC volt-
age on the harness side of the connector
between pins A & B and then between C & D. A
voltage (10 to 16 VAC) should be read by the
digital voltmeter for each pair of wires. If the
reading is present on all of the wire pairs there is
a good signal coming from the control system.
3. If the reading is not present on one or more of
the wire pairs, check the wiring between the
control system and the CSMV connector, or
check the control system for proper model num-
ber Configuration.
b. Diagnostics - Stepper Motor
The valve stepper motor may be tested using a stepper
motor drive tester or ohmmeter.
1. To test with a stepper motor drive tester (Carrier
Transicold part number 07-00375-00), connect
the 4 pin test cable supplied with the tester to
the valve connector, refer to
Figure 8.35 , and
the cable wires to the tester in accordance with
wire and terminal color.
2. Set the step rate to 200 steps per second and
either open or close the valve. Each red LED
should light sequentially until all four are illumi-
nated. Any LED failing to illuminate indicates an
open on that leg and a need to replace the pis-
ton and drive motor assembly.
3. To test with an ohmmeter, check the winding
resistance between connector pin A & B and
then between C & D, see
Figure 8.35 . In normal
ambient, the resistance between the pins should
be 72 to 84 ohms. Also check each terminal to
the coil casing (ground). If an out of tolerance or
zero reading is observed, the piston and drive
motor assembly is to be replaced.
Figure 8.35 CSMV Coil
A1 A2
B1 B2
C2
C1
Body Screws
From Coil
To Compressor
1
2
A (BLACK) (WHITE) B
(RED) C
D (GREEN)