Carrier Complete Guide to Air Conditioner Models 38AKS028 and 38AKS044

Oil Pressure Safety Switch (OPS) Ð The OPS in the control circuit stops the compressor and unit, if proper oil pressure differential is not established at start-up or main- tained during operation. If OPS stops the unit, determine the cause and correct before restarting unit. Failure to do so will constitute abuse. Equipment failure due to abuse may void the warranty.

Compressor Protection

CIRCUIT BREAKER Ð Calibrated trip manual reset, am- bient compensated, magnetic breaker protects against motor overload and locked rotor conditions.

CONTROL MODULE TIMER Ð This control protects com- pressor against short cycling. See Sequence of Operation on page 17.

CRANKCASE HEATER Ð This minimizes absorption of liquid refrigerant by oil in crankcase during brief or ex- tended shutdown periods.

IMPORTANT: Never open any switch or disconnect that deenergizes the crankcase heater unless unit is be- ing serviced or is to be shut down for a prolonged pe- riod. After a prolonged shutdown on a service job, en- ergize the crankcase heater for 24 hours before starting the compressor.

High-Pressure Switch Ð This switch has ®xed, non- adjustable settings. Switch is mounted on the compressor (See Table 4).

Low-Pressure Switch Ð This switch has ®xed, non- adjustable settings. Switch is mounted on the compressor. (See Table 4.)

Table 4 Ð Pressure Switch Settings, psig (kPa)

	HIGH PRESSURE			LOW PRESSURE
Cutout		Cut-in		Cutout		Cut-in
426	± 7	320	± 20	27	± 3	44	±	5
(2937	± 48)	(2206	± 138)	(186	± 21)	(303	±	34)

Winter Start Control Ð Bypass relay timer bypasses low-pressure switch for 2 minutes on unit start-up.

Head Pressure Control Ð Control maintains ad- equate discharge pressure under low ambient temperature con- ditions. See Table 5.

FAN CYCLING Ð These 38AKS units have standard pro- vision for fully automatic intermediate-season head pressure control through condenser fan cycling. Fan no. 2 is cycled by a fan cycling pressure switch (FCPS) which responds to variation in discharge pressure. The pressure sensor is lo- cated in the liquid line of the refrigerant circuit. Fan no. 3 cycling is controlled by outdoor-air temperature through an air temperature switch (ATS) (38AKS044 units only).

Table 5 Ð Minimum Outdoor-Air

Operating Temperature

		COND	MIN OUTDOOR TEMP, F (C)
UNIT	COMPR	TEMP,	Standard		Low Ambient
38AKS	CAP. (%)				Control
		F (C)	Unit
					(Motormaster )
028	100	90 (32)	31	(±1)	±20 (±29)
	67	80 (27)	35	(2)	±20 (±29)
	33	70 (21)	43	(6)	±20 (±29)
034	100	90 (32)	30	(±1)	±20 (±29)
	67	80 (27)	34	(1)	±20 (±29)
	33	70 (21)	42	(6)	±20 (±29)
044	100	90 (32)	25	(±4)	±20 (±29)
	67	80 (27)	30	(±1)	±20 (±29)
	33	70 (21)	35	(2)	±20 (±29)

The ATS is located in the lower divider panel between the compressor compartment and condenser section. Through a hole in the panel, the sensing element is exposed to air en- tering the no. 1 fan compartment. Fan no. 1 is noncycling. Table 6 shows the operating settings of the FCPS and the ATS.

Table 6 Ð Fan Cycling Controls

CONTROL BY	SWITCH OPENS	SWITCH CLOSES
Temp, F (C)	70 ± 3 (21 ± 1.7)	80 ± 3 (27 ±	1.7)
Pressure,	160 ± 10 (1103 ± 69)	260 ± 15 (1793	± 103)
psig (kPa)

NOTE: See Fig. 6 and 7 for fan arrangement.

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