Carrier 69NT20-531-300 manual Precheck Procedure

6.20.1 Precheck Procedure

a. Check unit for abnormal operation.

b. Check charge. If refrigerant is low repair as required and again check operation.

c. 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.

d. 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 control- ler and drive module are attempting to close the valve, and may serve as a quick indication that the drive is in working order.

e.Operation of the valve may be checked using the con- troller valve override program, function code Cd41. Refer to paragraph 6.19 for valve override test in- structions.

6.20.2Checking The Stepper valve a. Checking with ohmmeter

Disconnect the four 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 the white/black (c-d terminals) leads. If an infinite or zero reading occurs, check connections and replace the motor.

b. Checking with SMA-12 portable stepper drive tester

The SMA-12 portable stepper drive tester (Carrier Transicold P/N 07-00375-00) is a battery operated stepper drive which will open and close the SMV, which allows a more thorough check of the operating mechanism.

To check operation:

1.Stop the unit, disconnect the four pin connector from the stepper module to the valve (see Figure 6-17) and attach the SMA-12 stepper drive to the connector go- ing to the valve.

2.Set the SMA-12 pulse per second (PPS) to one PPS and either open or close valve. Each LED should light sequentially until all four are lit. Any LED fail-

ing to light indicates an open on that leg which indi- cates a poor connection or an open coil. Repair or re- place as required to achieve proper operation.

CAUTION

The scroll compressor achieves low suction pressure very quickly. Do not operate the compressor in a deep vacuum, internal dam- age will result.

3.Restart unit, set the step rate to 200 PPS on SMA-12 for the valve, and close stepper valve while watching the suction gauge. Within one minute the suction pressure will go into a vacuum. This is an indication that the valve is moving.

4.If no change in suction pressure is detected, check for resistance (refer to step 6.20.2), and check con- nections for proper continuity and retest. If the valve is functioning and all connections and motor resist- ance are good, check the controller and expansion module.

CAUTION

DO NOT disassemble piston from NEW suc- tion modulating valve powerhead assembly. Doing so may result in damage to piston.

5.If the valve is determined as faulty after completing the above steps, perform a low side pump down. Re- move valve powerhead assembly, and replace with a NEW valve powerhead assembly, torque nut to 35 ft- lb, evacuate low side, and open all service valves.

6.21CONTROLLER AND EXPANSION MODULE 6.21.1 Handling Modules

CAUTION

Do not remove wire harnesses from module unless you are grounded to the unit frame with a static safe wrist strap.

CAUTION

Unplug all module connectors before per- forming arc welding on any part of the con- tainer.

The guidelines and cautions provided herein should be followed when handling the modules. These precautions and procedures should be implemented when replacing a module, when doing any arc welding on the unit, or when service to the refrigeration unit requires handling and removal of a module.

T-309 6-14