change any two leads to check the internal motor phas- ing. If the compressor runs backward for an extended period (15 to 30 minutes), the motor winding can over heat and cause the motor winding thermostats to open. This will cause a “compressor trip” diagnostic and stop the compressor.
11.Press the STOP key at the Human Interface Module in the unit control panel to stop the compressor operation.
12.Repeat steps 5 through 11 for each compressor stage and the appropriate condenser fans.
Refrigerant Charging
1.Attach a set of service gauges onto the suction and dis- charge gauge ports for each circuit. Refer to Figure
2.Open the Human Interface access door, located in the unit control panel, and press the SERVICE MODE key to display the first service screen. Refer to the latest edition of the
3.Use Table
Supply Fan (On)
Inlet Guide Vanes/VFD (100%, if applicable) OCC/UNOCC Relay (Unoccupied for VAV units) All Compressors for each circuit (On) Condenser Fans for each circuit (On)
4.Once the configuration for the components is complete, press the NEXT key until the LCD displays the “Start test in __Sec.” screen. Press the + key to designate the delay before the test is to start. This service test will begin after the TEST START key is pressed and the delay desig- nated in this step has elapsed. Press the ENTER key to confirm this choice.
Unit Start-Up (Continued)
Note: Do Not release refrigerant to the atmosphere! If adding or removing refrigerant is required, the service technician must comply with all Federal, State and local laws. Refer to general service bulletin
7.Verify that the oil level in each compressor is correct. The oil level may be down to the bottom of the sightglass but should never be above the sightglass.
8.Press the STOP key at the Human Interface Module in the unit control panel to stop the system operation.
9.Repeat steps 1 through 8 for the number 2 refrigeration circuit.
10.After shutting the system off, check the compressor's oil’s appearance. Discoloration of the oil indicates that an abnormal condition has occurred. If the oil is dark and smells burnt, it has overheated because of: compressor is operating at extremely high condensing temperatures; high superheat; a compressor mechanical failure; or, oc- currence of a motor burnout.
If the oil is black and contains metal flakes, a mechanical failure has occurred. This symptom is often accompanied by a high compressor amperage draw.
If a motor burnout is suspected, use an acid test kit to check the condition of the oil. Test results will indicate an acid level exceeding 0.05 mg KOH/g if a burnout oc- curred.
The scroll compressor uses Trane
Compressor Crankcase Heaters
9and 10 ton scroll compressors have a
WARNING
Rotating Components!
Disconnect all electric power, including remote discon- nects before servicing. Follow proper lockout/tagout procedures to ensure the power can not be inadvert- ently energized. Failure to disconnect power before ser- vicing could result in death or serious injury.
5.Press the TEST START key to start the test. Remember that the delay designated in step 4 must elapse before the system will begin to operate.
6.After all of the compressors and condenser fans for the number 1 circuit have been operating for approximately 30 minutes, observe the operating pressures. Use the appropriate pressure curve in Tables
Compressor Operational Sounds
Because of the scroll compressor design, it emits a higher frequency tone (sound) than a reciprocating compressor. It is designed to accommodate liquids, both oil and refriger- ant, without causing compressor damage. The following dis- cussion describes some of the operational sounds that dif- ferentiate it from those typically associated with a recipro- cating compressor. These sounds do not affect the opera- tion or reliability of the compressor.
At Shutdown
When a Scroll compressor shuts down, the gas within the scroll expands and causes momentary reverse rotation until the discharge check valve closes. This results in a “flutter” type sound.
At Low Ambient Start-Up
When the compressor starts up under low ambient condi- tions, the initial flow rate of the compressor is low due to the low condensing pressure. This causes a low differential across the thermal expansion valve that limits its capacity. Under these conditions, it is not unusual to hear the com- pressor rattle until the suction pressure climbs and the flow rate increases.
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