Carrier 38AKS013-024 specifications Operating Sequence, Service

OPERATING SEQUENCE

Cooling Ð When the ®rst stage (TC1) of the cooling ther- mostat closes, the timer starts. After approximately 3 seconds, the timer expires, energizing the compressor and fan motor no. 1. When the liquid pressure builds to approxi- mately 257 psig (1772 kPa), fan motor no. 2 is energized.

On demand for additional cooling capacity, the second stage (TC2) of the cooling thermostat closes, energizing a ®eld- supplied liquid line solenoid (LLS) valve, which opens. This increases the suction pressure, causing the compressor to operate at higher capacity.

When fan switch is set at AUTO, the indoor unit fan cycles with the compressor. When the switch is set at ON, the indoor unit fan runs continuously.

At shutdown, the Time Guard II timer prevents the com- pressor from restarting for approximately 5 minutes.

When installed, a ®eld-supplied solenoid valve (wired in parallel with the compressor contactor coil), shuts off the liq- uid line to prevent refrigerant migration back to the com- pressor during the off cycle.

Heating Ð The heating thermostat (TH) energizes a ®eld- supplied relay which operates heating controls and ener- gizes the indoor unit relay. When the fan switch is set at AUTO, the indoor unit fan cycles with the heating control. The indoor unit fan runs continuously when the fan switch is set at ON.

Causes of complete unit shutdown are: interruption of sup- plied power, open compressor internal protector (IP), open control circuit breaker, or an open high- or low-pressure safety switch.

Fan Cycling Ð Head pressure control is accomplished by cycling the fans. The no. 2 fan responds to liquid line pressure, cycling on at approximately 255 psig (1758 kPa) and off at approximately 160 psig (1103 kPa).

Winter Start Control (If Installed) Ð When the com- pressor starts, the control's bypass timer contacts close for 150 seconds, thereby bypassing the low-pressure switch dur- ing start-up. After 150 seconds, the bypass timer contacts open and the low-pressure switch is restored to the safety circuit.

SERVICE

Capacity Control Ð A suction pressure-actuated unloader controls 2 cylinders and provides capacity control. Unloaders are factory set (see Tables 1A-1D), but can be ®eld adjusted as described in the 2 following sections.

CONTROL SET POINT (cylinder load point) is adjustable from 0 to 85 psig (586 kPa). To adjust, turn control set point adjustment nut (Fig. 13) clockwise to its bottom stop. In this position, set point is 85 psig (586 kPa). Next, turn adjust- ment counterclockwise to desired control set point. Every full turn counterclockwise decreases set point by 7.5 psig (51.7 kPa).

PRESSURE DIFFERENTIAL (difference between cylinder load and unload points) is adjustable from 6 to 22 psig (41.4 to 152 kPag). To adjust, turn pressure differential ad- justment screw (Fig. 13) counterclockwise to its back stop position. In this position, differential is 6 psig (41.4 kPag). Next, turn adjustment clockwise to desired pressure differ- ential setting. Every full turn clockwise increases differen- tial by 1.5 psig (10.3 kPag).

Head Pressure Control Ð Fan cycling is a standard feature. The no. 2 fan cycles in response to changes in liquid pressure. The switch cycles the fan off at 160 ± 10 psig (1103 ± 69 kPa) as pressure decreases, and cycles it back on at 255 ± 10 psig (1758 ± 69 kPa).

Fig. 13 Ð Compressor Capacity Control Unloader

Time Guard II Circuit Ð Circuit prevents short- cycling by providing a delay of approximately 5 minutes before restarting compressor after shutdown from safety device action.

On start-up, the Time Guard II timer causes a delay of approximately 3 seconds after thermostat closes.

On compressor shutdown, the timer recycles for approxi- mately 5 minutes. During this time, the compressor cannot restart.

Refer to Fig. 14 and to label diagram on unit.

Fig. 14 Ð Timer Sequence Chart

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