Carrier 38AE012 Installation, Start-up And Service Instructions Manual

Also see for 38AE012: Installation, Start-Up and Service Instructions

Contents

Carrier 38AE012 Installation, Start-up And Service Instructions Manual Manual pdf 13 page image

Check Operation — Verify operation of all safety con-trols. Replace all service panels. Be sure that control panelcover is closed tightly.OPERATING SEQUENCECooling — When the first stage (TC1) of the cooling ther-mostat closes, the timer starts. After approximately 3 sec-onds, the timer activates the compressor and fan motor no.1 contactor. 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 field-supplied liquid line solenoid (LLS) valve, which opens. Thisincreases the suction pressure, causing the compressor to op-erate at higher capacity.When fan switch is set at AUTO, the indoor-air fan cycleswith the compressor. When the switch is set at CONT, theindoor-air fan runs continuously.At shutdown, the Time Guardt II timer prevents the com-pressor from restarting for approximately 5 minutes.When installed, a field-supplied solenoid valve (wired inparallel 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 — The heating thermostat (TH) energizes a field-supplied relay which operates heating controls and ener-gizes the indoor-fan relay. When the fan switch is set at AUTO,the indoor-air fan cycles with the heating control. The indoor-air fan runs continuously when the fan switch is set at CONT.Fan Cycling — Head pressure control is accomplishedby cycling the fans. The no. 2 fan responds to liquid linepressure, cycling on at approximately 257 psig (1772 kPa)and off at approximately 126 psig (869 kPa).Winter Start Control (If Installed) — When the com-pressor starts, the control’s bypass timer contacts close for150 seconds, thereby bypassing the low-pressure switch dur-ing start-up. After 150 seconds, the bypass timer contactsopen and the low-pressure switch is restored to the safetycircuit.SERVICECapacity Control — A suction pressure-actuated un-loader controls 2 cylinders and provides capacity control. Un-loaders are factory set (see Tables 1A-1D), but can be fieldadjusted as described in the 2 following sections.CONTROL SET POINT (cylinder load point) is adjustablefrom 0 to 85 psig (586 kPa). To adjust, turn control set pointadjustment nut (Fig. 12) clockwise to its bottom stop. In thisposition, set point is 85 psig (586 kPa). Next, turn adjust-ment counterclockwise to desired control set point. Everyfull turn counterclockwise decreases set point by7.5 psig (51.7 kPa).PRESSURE DIFFERENTIAL (difference between cylinderload and unload points) is adjustable from 6 to 22 psig (41.4to 152 kPa). To adjust, turn pressure differential adjustmentscrew (Fig. 12) counterclockwise to its back stop position.In this position, differential is 6 psig (41.4 kPa). Next, turnadjustment clockwise to desired pressure differential setting.Every full turn clockwise increases differential by 1.5 psig(10.3 kPa).Head Pressure Control — Fan cycling is a standardfeature. The no. 2 fan cycles in response to changes in liquidpressure. The switch cycles the fan off at 126 ± 4 psig (869± 28 kPa) as pressure decreases, and cycles it back on at 257(+5, −0) psig (1772 [+103, −0] kPa).Time Guard II Circuit — Prevents short-cycling by pro-viding a delay of approximately 5 minutes before restartingcompressor after shutdown from safety device action.On start-up, the Time Guard II timer causes a delay ofapproximately 3 seconds after thermostat closes.On compressor shutdown, the timer recycles for approxi-mately 5 minutes. During this time, the compressor cannotrestart.Refer to Fig. 13 and to label diagram on unit.Winter-Start Control (If Required) — Install Ac-cessory Package 38AE900021.Crankcase Heater — The heater prevents refrigerantmigration and compressor oil dilution during shutdown when-ever compressor is not operating. It is wired into the controlcircuit, and cycles with the compressor; the heater is off whencompressor is running, and on when compressor is off.Both compressor service valves must be closed wheneverthe crankcase heater is deenergized for more than 6 hours.The crankcase heater is operable as long as the control cir-cuit is energized.Fig. 12 — Compressor Capacity Control UnloaderFig. 13 — Timer Sequence Chart13