Carrier 69NT40-541-306, Операция и обслуживание

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T-354 7–28
7.19 SUCTION MODULATION VALVE (SMV)
On start up of the unit, the valve will reset to a known open position. This is accomplished by assuming the valve
was fully open, driving it fully closed, resetting the percentage open to zero, then opening to a known 21% staging
position.
Figure 7.25 Suction Modulation Valve (SMV)
7.19.1 Pre-check Procedure
1. Check unit for abnormal operation.
2. Check charge. If refrigerant is low repair as required and again check operation.
3. If sufficient capacity cannot be maintained or unit is tripping excessively on high pressure switch (HPS) in
high ambients, check coils and clean if required.
4. If capacity or control cannot be maintained, turn unit OFF, then back ON. This will reset the valve in the
event the controller lost communication with the valve, and may correct the problem.
NOTE
Carefully listen to the valve. During reset, the valve will make a ratcheting noise that may be heard or
felt as it is attempting to close. If this can be heard or felt, it indicates that the controller and drive mod-
ule are attempting to close the valve, and may serve as a quick indication that the drive module is in
working order.
5. During the first few minutes of unit operation, compressor reliability enhancement logic (CREL) may be in
effect. This places the valve at a 21% staging position and is sufficient to drive the temperature of the supply
probe down several degrees during this inter val.
6. After the CREL time-out has been met, the valve will start responding to the control logic and open or close
relative to the demand. Scrutinize the unit operation for a few minutes. While in pulldown, the unit will open
the SMV to a maximum discharge pressure of 325 psig in high ambient conditions, or as much as the cur-
rent setting and control logic will allow. The current level should be high. A lower discharge pressure will be
seen in lower ambient temperatures. Once the unit has reached set point, the SMV will go into control
mode. Both the discharge/suction pressures, and current draw will go significantly lower. Once below set
point, the suction pressure should go into a vacuum within several minutes. Should the operation differ as
mentioned, the SMV, controller, or wiring, may be faulty.
7. Check for correct wire location at the stepper motor plug and the environmental connector (EC). Make sure
that the wires terminate in accordance with the wire markings (addresses).
8. Attach a manifold gauge set (refer to Section 7.3 ). If the unit is operating in the perishable mode, proceed to
step i. If the unit is operating in the frozen mode, proceed to step j.
9. 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 approximately
one minute. Record readings on gauges and current draw. The current draw and pressures should go up.
Place set point 0.5

C (0.9

F) above current box temperature to fully modulate valve, and run for approxi-
mately 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.
2-1/8 inch Nut