Carrier TRANSICOLD Vector 8500 Operation & Service Manual Download

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8–27

62-11640

8.8.6

Compressor Suction Modulation Valve
(CSMV)

The purpose of the CSMV (see

Figure 8.22

) is to main-

tain the compressor within its operating envelope, max-
imize unit capacity and fuel economy, maintain
temperature control and engine power.

Figure 8.22 Suction Modulation Valve

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 3.6

). 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 (SMV)

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 07-00375-00SV), connect
the 4 pin test cable supplied with the tester to the
valve connector, and the cable wires to the tester
in accordance with wire and terminal color.

2. Set the step rate to 150 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 8.23

. In normal

ambient, the resistance between the pins should
be 65 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 8.23 CSMV Coil

c. Diagnostics - Valve

NOTE

If the valve failed pretest and passed the
preceding diagnostic testing, this is an indi-
cation that the valve mechanism is damaged
and the internal motor/piston assembly is to
be replaced.

1. To test the valve internal mechanism, install a

manifold gauge set on the suction service valve
and a stepper motor drive tester.

2. Start the unit, set the step rate to 150 steps per

second and close the valve while watching the
suction pressure. Within one minute the suction
pressure should begin to fall. Place the STOP/
RUN-OFF switch in the OFF position before the
reading enters a vacuum.

3. If the suction pressure does not change, this is

an indication the valve is stuck and the internal
motor/piston assembly is to be replaced.

d. Replace the Internal Motor/Piston Assembly

1. Pump down the low side. Refer to

Section

8.6.2

2. Remove internal motor/piston assembly and

replace with a new assembly and gaskets. The
motor/piston assembly should be set to 100%
open when received from the warehouse. This
is to ensure the valve seal is not damaged when
it is installed. Ensure the valve is fully open by
using the stepper motor tester to manually open
the valve to 100% before it is installed. Ensure

4 Pin Connector

Drive & Motor
Assembly

Screws

Body

A (BLACK)

(WHITE) B

(RED) C

D (GREEN)