Carrier 38AUZ*07 Series Installation, Start-up And Service Instructions Manual

Contents

23OPERATING SEQUENCEBase Unit ControlsIndoor (Supply) FanThe indoor fan contactor (IFC) is remotely located at the fancoil or fan section. If the thermostat fan operation is selectedas Continuous, the IFC is energized and the indoor (supply)fan motor runs continuously. If the thermostat fan operationis selected as Automatic, the IFC will be energized on a callfor Cooling; indoor (supply) fan motor runs. Whenthermostat call for Cooling is satisfied, the IFC isde-energized and indoor (supply) fan motor stops.Cooling, Unit Without Economizer38AUDOn a thermostat call for Cooling, IFC will be energizedand indoor (supply) fan motor runs. Thermostat output Y1is energized; terminal Y1 at 38AUD unit receives 24-v.24-v received at CADM1 terminal Y. If anti-recycle timedelay period has not expired, CADM1 relay will remainopen, de-energizing Solenoid Valve Relay 1 (SVR1) andpreventing compressor start. When safety pressureswitches are closed and CADM1 time delay expires,CADM1 relay closes, SVR1 and compressor contactor C1are energized; liquid line solenoid valve LLSV1 opens, alloutdoor fan motors start and Circuit 1 compressor starts.On a thermostat calling for Stage 2 Cooling, thermostatoutput Y2 is energized; terminal Y2 at 38AUD unitreceives 24-v. 24-v received at CADM2 terminal Y. Ifanti-recycle time delay period has not expired, CADM2relay will remain open, de-energizing Solenoid ValveRelay 2 (SVR2) and preventing compressor start. Whensafety pressure switches are closed and CADM2 timedelay expires, CADM2 relay closes, SVR2 andcompressor contactor C2 are energized; liquid linesolenoid valve LLSV2 opens and Circuit 2 compressorstarts.As space cooling load is satisfied, thermostat outputs Y2and Y1 are de--energized, removing 24-v at 38AUDterminals Y2 and Y1. Circuit 2 compressor stops on Y2opening; SVR2 is de-energized and LLSV2 closes.CADM2 begins its three-minute anti-recycle time delay.On Y1 opening, Circuit 1 compressor stops, all outdoorfan motors stop and SVR1 relay is de-energized. Liquidline solenoid valve LLSV1 is de-energized and valvecloses. CADM1 begins its three-minute anti-recycle timedelay.If either the Low Pressure Switch or High Pressure Switchopens while thermostat output Y1 or Y2 remain energized,the compressor contactor is de-energized, the compressorstops and liquid line solenoid is de-energized (valvecloses). CADM initiates a TRIP event (cooling demandsensed at CADM terminal Y but no current is measured atT1, T2, T3 motor sensors); CADM relay opens and REDLED is illuminated. TRIP condition maintains lockout ofcompressor operation until CADM is manually reset.Reset CADM by cycling unit main power.Complete system shutdown may be caused by loss ofmain power, open compressor internal overload, openlow-pressure or high-pressure switch, or a fault detectedby the CADM logic. Compressor operation withoutcooling may indicate the compressor’s ASTP feature isactive; disconnect unit power and allow compressor tocool. See Service section for further details.Cooling, Unit With EconomizerRefer to fan coil unit installation instructions andeconomizer accessory installation instructions for operatingsequences when system is equipped with accessoryeconomizer.HeatingRefer to fan coil unit installation instructions andaccessory heating device installation instructions foroperating sequences in heating mode.38AUD