Carrier 48/50AJ specifications Advanced Scroll Temperature Protection Label

temperature (OAT) rises above 75 F or the highest active cir- cuit saturated condensing temperature (SCT) rises above the HPSP and remains on until the condition is repaired regardless of the OAT and SCT values.

Any time the alert occurs, a strike is called out on the affect- ed compressor. If three successive strikes occur the compressor will be locked out requiring a manual reset or power reset of the circuit board. The clearing of strikes during compressor op- eration is a combination of 3 complete cycles or 15 continuous minutes of run time operation. If there are one or two strikes on the compressor and three short cycles (ON-OFF, ON-OFF, ON-OFF) less than 15 minutes each occur, the strikes are reset to zero for the affected compressor. If the compressor turns on and runs for 15 minutes straight with no compressor failure, the compressor strikes are cleared.

Additionally, some units contain Copeland compressors equipped with advanced scroll temperature protection (ASTP). A label located above the terminal box identifies Copeland Scroll compressor models that contain this technology. See Fig. 5. Advanced scroll temperature protection is a form of in- ternal discharge temperature protection that unloads the scroll compressor when the internal temperature reaches approxi- mately 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. 6.

To manually reset ASTP, the compressor should be stopped and allowed to cool. If the compressor is not stopped, the motor

Fig. 5 — Advanced Scroll Temperature

Protection Label

		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 tem- perature, and the presence of a sound blanket will increase cool- down times.

Fig. 6 — Recommended Minimum Cool-Down

Time After Compressor is Stopped*

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.

COMPRESSOR TIME GUARDS — The control will not al- low any output relay to come on within 3 seconds of any other output relay. For outputs connected to the compressors, the con- trol will use a Compressor Minimum OFF Time of 2 minutes, a Compressor Minimum ON Time of 3 minutes and a Minimum Delay before turning on another compressor of 10 seconds.

COOL MODE SELECTION PROCESS — The A Series ComfortLink™ controls offer three distinct methods by which it may select a cooling mode.

1.Thermostat (C.TYP=3 and 4): The thermostat does not depend upon the state of occupancy and the modes are called out directly by the discrete inputs from the thermo- stat (Inputs→STAT→Y1 and Y2).

2.Occupied VAV cooling types (C.TYP=1 and 2) are called out in the occupied period (Operating Modes→MODE→ OCC=ON).

3.Unoccupied VAV cooling types (C.TYP=1 and 2) are called out in the unoccupied period (Operating

Modes→MODE→OCC=OFF). They are also used for space sensor control types (C.TYP=5 and 6) in both the occupied and unoccupied periods.

This section is devoted to the process of cooling mode determination for the three types outlined above.

VAV Cool Mode Selection during the Occupied Period (C.TYP = 1,2 and Operating Modes→MODE→OCC =ON)

—There is no difference in the selection of a cooling mode for either VAV-RAT or VAV-SPT in the occupied period. The actual selection of a cool mode, for both control types, is based upon the controlling return-air temperature (Temperatures→AIR.T →CTRL→R.TMP). Typically this is the same as the return air temperature thermistor (Temperatures→AIR.T→RAT) except when under CCN Linkage.

VAV Occupied Cool Mode Evaluation Configuration — There

are VAV occupied cooling offsets under Setpoints.

ITEM	EXPANSION	RANGE	UNITS	CCN POINT	DEFAULT
V.C.ON	VAV Occ.	0-25	^F	VAVOCON	3.5
V.C.OF	Cool On Delta
	VAV Occ.	1-25	^F	VAVOCOFF	2
	Cool Off Delta

Cool Mode Determination — If the machine control type (Configuration→ UNIT→C.TYP) = 1 (VAV-RAT) or 2 (VAV- SPT) and the control is occupied (Operating Modes →MODE→OCC=ON), then the unit will not follow the occu- pied cooling set point (OCSP). Instead, the control will follow two offsets in the determination of an occupied VAV cooling mode (Setpoints→V.C.ON and Setpoints→V.C.OF), applying them to the low-heat off trip point and comparing the resulting temperature to the return-air temperature.

The Setpoints→V.C.ON (VAV cool mode on offset) and Setpoints→V.C.OF (VAV cool mode off offset) offsets are used in conjunction with the low heat mode off trip point to determine when to bring cooling on and off and in enforcing a true “vent” mode between heating and cooling. See Fig. 7. The occupied cooling set point is not used in the determination of the cool mode. The occupied cooling set point is used for supply air reset only.

OHSP			V.C. ON		V.C. OF
	L.H.ON
		L.H.OF
				A48-7700

Fig. 7 — VAV Occupied Period Trip Logic

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