Bryant 575B, 575C Iii. Liquid Line Solenoid, Iv. Accumulator, Start-Up, Ii. Compressor Overload

Before starting the unit, charge liquid refrigerant into the high side of the system through the liquid service valve. Allow high and low side pressures to equalize before starting compressor. If pressures do not equalize readily, charge vapor on low side of system to assure charge in the evapora- tor. Refer to GTAC II, Module 5, Charging, Recovery, Recy- cling, and Reclamation for liquid charging procedures.

III. LIQUID LINE SOLENOID

To minimize refrigerant migration to the compressor during the heat pump OFF cycle, the 575B,C unit must have a bi-flow liquid line solenoid valve (field supplied). The valve opens when the compressor is energized, and closes when the compressor is deenergized. This reduces compressor flooded starts, thus significantly increasing compressor life.

IV. ACCUMULATOR

The unit accumulator controls the rate of liquid refrigerant to the compressor during heat pump operation.

The 541A accumulator features a unique method for returning oil to the compressor. The oil return mechanism is external to the accumulator. The mixture of oil and refriger- ant is metered to the compressor by a brass orifice which is removable and cleanable. The oil return mechanism also contains a solenoid valve that opens when the compressor is ON and closes when the compressor is OFF. This keeps the liquid refrigerant stored in the accumulator from draining to the compressor during the heat pump OFF cycle, which further protects the compressor against flooded starts.

START-UP

CAUTION: Compressor crankcase heater must be on for 24 hours before start-up. After the heater has been on for 24 hours, the unit can be started.

CAUTION: Prior to starting compressor, a preliminary charge of refrigerant must be added to avoid possible compressor damage.

I. COMPRESSOR ROTATION (575B,C Units)

On 3-phase units with scroll compressors, it is important to be certain compressor is rotating in the proper direction. To determine whether or not compressor is rotating in the proper direction:

1.Connect service gages to suction and discharge pres- sure fittings.

2.Energize the compressor.

3.The suction pressure should drop and the discharge pressure should rise, as is normal on any start-up.

If the suction pressure does not drop and the discharge pressure does not rise to normal levels:

1.Note that the condenser fan is probably also rotating in the wrong direction.

2.Turn off power to the unit, tag disconnect.

3.Reverse any two of the unit power leads.

4.Reapply power to the compressor, verify correct pressures.

The suction and discharge pressure levels should now move to their normal start-up levels.

II. COMPRESSOR OVERLOAD

This overload interrupts power to the compressor when either the current or internal motor winding temperature

becomes excessive, and automatically resets when the internal temperature drops to a safe level. This overload usually resets within 60 minutes (or longer). If the internal overload is suspected of being open, disconnect the electrical power to the unit and check the circuit through the overload with an ohmmeter or continuity tester.

III.ADVANCED SCROLL TEMPERATURE PROTECTION (ASTP)

Advanced Scroll Temperature Protection (ASTP) is a form of internal discharge temperature protection that unloads the scroll compressor when the internal temperature reaches approximately 300 F. At this temperature, an internal bi- metal disk valve opens and causes the scroll elements to sep- arate, which stops compression. Suction and discharge pres- sures balance while the motor continues to run. The longer the compressor runs unloaded, the longer it must cool before the bi-metal disk resets. See Fig. 17.

To manually reset ASTP, the compressor should be stopped and allowed to cool. If the compressor is not stopped, the motor will run until the motor protector trips, which occurs up to 90 minutes later. Advanced Scroll Temperature Protec- tion will reset automatically before the motor protector resets, which may take up to 2 hours. A label located above the terminal box identifies Copeland Scroll compressor models (ZR94, 108 and 125) that contain this technology. See Fig. 18.

		120
		110
Time		100
		90
Recommended Cooling
	(Minutes)	80
		70
		60
		50
		40
		30
		20
		10
		0
		0	10	20	30	40	50	60	70	80	90
				Compressor Unloaded Run Time (Minutes)

*Times are approximate.

NOTE: Various factors, including high humidity, high ambient tempera- ture, and the presence of a sound blanket will increase cool-down times.

Fig. 17 — Recommended Minimum Cool-Down Time After

Compressor is Stopped*

Fig. 18 — Advanced Scroll Temperature Protection Label

—16—