Carrier 69NT40-541-306 Operation And Service
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7–29 T-35410. Record new gauge readings and current draw. The suction pressure should go into a vacuum and the cur-rent draw should have gone down. If little or no change to the suction pressure or current draw occurs, thisis an indication of a malfunctioning SMV.11. Frozen operation: In frozen mode the valve tends to stay open as much as possible. Again, this is depen-dent upon current limit setting and control logic. Turn the unit OFF and ON, as in the perishable mode, andwatch the gauges. The valve will run at 21% open if CREL logic is active, and will open to maximum allowable after this. Depending on ambient conditions, there should be an increase in suction pressure and cur-rent draw as the valve opens. However, at times, this may be difficult to fully determine.12. If the unit still does not operate properly, stop unit and proceed to the following step to check out the SMVsystem.7.19.2 Checking the Stepper ValveChecking with ohmmeterDisconnect 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 thewhite/black (c-d terminals) leads. If an infinite or zero reading occurs, check connections and replace the motor. Ifnear normal or normal reading occurs, proceed to Section 7.19.3 to check out the controller.Checking with SMA-12 portable stepper drive testerThe SMA-12 portable stepper drive tester (Carrier Transicold P/N 07-00375-00) is a battery-operated stepper drivethat will open and close the SMV, allowing a more thorough check of the motor. To check operation:1. Stop the unit, disconnect the 4-pin connector from the stepper module to the valve (see Figure 7.25) andattach 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 lightsequentially until all four are lit. Any LED failing to light indicates an open on that leg, which indicates a poorconnection or an open coil. Repair or replace as required to achieve proper operation.3. Restart unit, set the step rate to 200 PPS on SMA-12 for the valve, and close stepper valve while watchingthe suction gauge. Within one minute the suction pressure will go into a vacuum. This is an indication thatthe valve is moving.4. If no change in suction pressure is detected, check for resistance (refer to Section 7.19.2), and check con-nections for proper continuity and retest. If the valve is functioning, and all connections and motor resistanceare good, check the drive module (refer to Section 7.19.3).5. If the valve is determined to be faulty after completing the above steps, perform a low side pump down.Remove valve powerhead assembly, 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 suction modulating valve powerhead assembly. Doingso may result in damage to piston.7.19.3 Checking the Controller1. Turn unit OFF.2. With voltmeter set to read 20 volts DC, attach the positive lead to MC1 of the 4-pin connector and the nega-tive lead to the TP9. Turn ON unit and watch the volt meter. After a short delay, the reading should remainunchanged at 0 volts. If 5VDC, check jumper wire from MC1 to MC8 is in place; if not, install and retest.7.19.4 Emergency Repair ProceduresIn the event that the SMV system has a failure and replacement components are not readily available, the systemcan be bypassed by removing the valve piston. To remove the piston, do the following:1. Perform a low side pump down (refer to Section 7.4).2. Remove SMV powerhead by loosening the 2-1/8 inch diameter nut (see Figure 7.25) to relieve any pres-sure and then sliding the powerhead out. |
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