Carrier Complete Guide to 38AU Air Conditioner Features and Maintenance

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 may require up to 60 minutes (or longer) to reset. 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.

Advanced Scroll Temperature Protection (ASTP) —

	A label located above the terminal box identifies Copeland
	Scroll compressor models that contain this technology. See
	Fig. 20. Advanced Scroll Temperature Protection (ASTP) is
	a form of internal discharge temperature protection, that
38AU	unloads the scroll compressor when the internal temperature
	reaches approximately 149_C (300_F). At this temperature,
	an internal bi-metal disk valve opens and causes the scroll
	elements to separate, which stops compression. Suction and
	discharge pressures 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. 21.

C10080

Fig. 20 - Advanced Scroll Temperature Protection Label

		120
Time*		110
		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 temperature, and the presence of a sound blanket will increase cool-down times.

C10081

Fig. 21 - Recommended Minimum Cool-Down Time

After Compressor is Stopped

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 Protection will reset automatically before the motor protector resets, which may take up to 2 hours.

Start Unit

Set the space thermostat to a set point above space temperature so that there is no demand for cooling. Close the 38AU disconnect switch. Only the crankcase heater will be energized.

Reset the space thermostat below ambient so that a call for cooling is ensured.

!CAUTION

UNIT DAMAGE HAZARD

Failure to follow this caution may result in equipment damage.

Never charge liquid into the low-pressure side of system. Do not overcharge. During charging or removal of refrigerant, be sure indoor-fan system is operating. Ensure both outdoor fan motors are running; bypass any Motormaster function.

Adjust Refrigerant Charge —

Refer to Cooling Charging Charts, Fig. 23 through Fig. 28. For applications with line lengths greater than 125 ft (38 m), contact Carrier representative. Vary refrigerant until the conditions of the chart are met. Note that the charging charts are different from the type normally used. The charts are based on charging the units to the correct subcooling for the various operating conditions. Accurate pressure gage and temperature sensing device are required. Connect the pressure gage to the service port on the liquid line service valve. Mount the temperature sensing device on the liquid line close to the liquid line service valve, and insulate it so that outdoor ambient temperature does not affect the reading. Indoor airflow must be within the unit’s normal operating range. Operate the unit for a minimum of 15 minutes. Ensure that pressure and temperature readings have stabilized. Plot the liquid pressure and temperature on chart and add or reduce the charge to meet the curve. Adjust the charge to conform with the charging chart, using the liquid pressure and temperature to read the chart.

Using plotted operating point:

If plotted operating condition is -	Adjust charge by -
BELOW the curve	REDUCE charge
ABOVE the curve	ADD charge

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