8
−
29
62-11389
cessor and the SMV connector, or check the micro-
processor for proper model number 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 to the valve connector, refer to
Table 8
−
3, and the cable wires to the tester in accord-
ance 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 se-
quentially until all four are illuminated. Any LED failing
to illuminate indicates an open on that leg and a need
to replace the piston and drive motor assembly .
3. To test with an ohmmeter, check the winding resist-
ance between connector pin 1A & 1B and then
between 2A & 2B, see Figure 8
−
27. In normal ambi-
ent, 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 ob-
served, the piston and drive motor assembly is to be
replaced.
1
2
1A (BLACK)
(WHITE) 1B
(RED) 2B
2A (GREEN)
Figure 8
−
27 CSMV Coil
c. Diagnostics - Valve
NOTE
If the valve failed pretest and passed the pre-
ceding diagnostic testing, this is an indication
that the valve internal mechanism is damaged
and the piston and motor assembly is to be re-
placed.
1. To test the valve internal mechanism, install a mani-
fold gauge set on the suction service valve and a
stepper motor drive tester.
2. Start the unit, set the step rate to 200 steps per
second and close the valve while watching the suc-
tion pressure. Within one minute the suction pressure
should begin to fall. Place the Main Power switch in
the OFF position before the reading enters a vacuum.
3. If the suction pressure does not change, this is an in-
dication the valve is stuck and the piston and drive
motor assembly is to be replaced.
d. Replacing the Drive and Motor Assembly
1. Pump down the low side. (Refer to section 8.6.2).
2. Remove valve piston and motor assembly and re-
place with a new assembly and gasket. The power
head should be set to 100% open when received from
the warehouse. This is to ensure the Teflon 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.
Torque nut to 47.4 Nm (35 ft-lb).
3. Leak check, evacuate the low side. Refer to Sections
8.6.3 and 8.6.4.
e. Emergency Repair Procedures:
In the event that the SMV system has a failure, and
replacement components are not readily available in an
emergency. A
LIMP-HOME
procedure can be done as
follows :
1. Install a manifold gauge set.
2. Pump down the low side. (Refer to section 8.6.2).
3. Remove SMV power head by loosening the 2-1/8
inch diameter nut (see Figure 8
−
26), and sliding the
power head out.
4. Remove the piston by loosening the Allen screw and
removing the piston and screw.
5. Install the power head assembly (without piston),
torque to 35 to 40 ft-lb (47 to 54 Nm).
6. Leak check and evacuate the low side. Refer to Sec-
tions 8.6.3 & 8.6.4.
7. Start the unit.
8. Adjust the suction service valve so that the approxi-
mate temperature OR current limit is maintained.
For perishable loads, it is recommended that the ad-
justment be made so that the available capacity is
slightly larger than the load, the unit will cycle OFF
and ON.
9. Once repair parts become available, repair as re-
quired.
8.8.6 Electronic Expansion Valve
The electronic expansion valve (EVXV - see
Figure 8
−
28) is a microprocessor driven device which
meters the flow of refrigerant into the coil. The flow
control provides: (a) response to match the evaporator
load and (b) prevention of liquid refrigerant return to the
compressor. Unless the valve is defective, it seldom
requires any maintenance.
NOTE
As a preliminary check, ensure the EVXV coil is
snapped down fully, and the coil retention tab is properly
seated in one of the valve body dimples.
