Carrier Gemini 38AU07 Series Installation Instructions Manual

Contents

32OPERATING SEQUENCEBase Unit ControlsINDOOR (SUPPLY) FANThe indoor fan contactor (IFC) is remotely located at thefan coil or fan section. If the thermostat fan operation is se-lected as Continuous, the IFC is energized and the indoor(supply) fan motor runs continuously. If the thermostat fanoperation is selected as Automatic, the IFC will be energizedon a call for Cooling; indoor (supply) fan motor runs. Whenthermostat call for Cooling is satisfied, the IFC is de-ener-gized and indoor (supply) fan motor stops.COOLING, UNIT WITHOUT ECONOMIZER38AUZ(A,B) (Single Circuit)On a thermostat call for Cooling, IFC will be energizedand indoor (supply) fan motor runs. Thermostat output Y1 isenergized; terminal Y1 at 38AUZ unit receives 24-v. 24-v re-ceived at CADM1 terminal Y. If anti-recycle time delay peri-od has not expired, CADM1 relay will remain open, de-ener-gizing Solenoid Valve Relay (SVR) and preventing compres-sor start. When safety pressure switches are closed andCADM1 time delay expires, CADM1 relay closes, SVR andcompressor contactor C1 are energized; liquid line solenoidvalve LLSV opens, all outdoor fan motors start and Compres-sor 1 starts.As space cooling load is satisfied, thermostat output Y1 isde-energized, removing 24-v at 38AUZ terminal Y1. On Y1opening, Compressor stops, all outdoor fan motors stop andSVR relay is de-energized. Liquid line solenoid valve is de-energized and valve closes. CADM1 begins its three-minuteanti-recycle time delay.38AUZ(D,E)07,08 (Single Circuit/2-Stage)On a thermostat call for Cooling, IFC will be energized andindoor (supply) fan motor runs. Thermostat output Y1 is ener-gized; terminal Y1 at either 38AUZ(D,E)07 or 38AUZ(D,E)08unit receives 24-v. 24-v received at CADM1 terminal Y. If anti-recycle time delay period has not expired, CADM1 relay willremain open, de-energizing Solenoid Valve Relay (SVR) andpreventing compressor start. When safety pressure switches areclosed and CADM1 time delay expires, CADM1 relay closes,SVR and compressor contactor C1are energized; liquid line so-lenoid valve LLSV opens, all outdoor fan motors start andCompressor 1 starts.On a thermostat calling for Stage 2 Cooling, thermostatoutput Y2 is energized; terminal Y2 at 38AUZ(D,E)07,08units receive 24-v. 24-v received at CADM1 terminal Y2.CADM1 DC SOL terminal outputs 24-vdc to the compressorloader plug (LDR) and the compressor operates at full loadcapacity.As space cooling load is satisfied, thermostat outputs Y2and Y1 are sequentially de-energized, removing 24-v at38AUZ(D,E)07,08 terminals Y2 and Y1. Compressor loaderplug is de-energized on Y2 opening. On Y1 opening, Com-pressor 1 stops, all outdoor fan motors stop and SVR relay isde-energized. Liquid line solenoid valve is de-energized andvalve closes. CADM1 begins its three-minute anti-recycletime delay.38AUD (Two Circuit)On a thermostat call for Cooling, IFC will be energizedand indoor (supply) fan motor runs. Thermostat output Y1 isenergized; terminal Y1 at 38AUD unit receives 24-v. 24-v re-ceived at CADM1 terminal Y. If anti-recycle time delay peri-od has not expired, CADM1 relay will remain open, de-ener-gizing Solenoid Valve Relay 1 (SVR1) and preventing com-pressor start. When safety pressure switches are closed andCADM1 time delay expires, CADM1 relay closes, SVR1 andcompressor contactor C1 are energized; liquid line solenoidvalve LLSV1 opens, all outdoor fan motors start and Circuit 1compressor starts.On a thermostat calling for Stage 2 Cooling, thermostatoutput Y2 is energized; terminal Y2 at 38AUD unit receives24-v. 24-v received at CADM2 terminal Y. If anti-recycletime delay period has not expired, CADM2 relay will remainopen, de-energizing Solenoid Valve Relay 2 (SVR2) and pre-venting compressor start. When safety pressure switches areclosed and CADM2 time delay expires, CADM2 relay closes,SVR2 and compressor contactor C2 are energized; liquid linesolenoid valve LLSV2 opens and Circuit 2 compressor starts.As space cooling load is satisfied, thermostat outputs Y2and Y1 are de-energized, removing 24-v at 38AUD terminalsY2 and Y1. Circuit 2 compressor stops on Y2 opening; SVR2is de-energized and LLSV2 closes. CADM2 begins its three-minute anti-recycle time delay. On Y1 opening, Circuit 1compressor stops, all outdoor fan motors stop and SVR1 re-lay is de-energized. Liquid line solenoid valve LLSV1 is de-energized and valve closes. CADM1 begins its three-minuteanti-recycle time delay.38AUDC12, UNIT WITH HOT GAS BYPASS (HGBP)Figure 33 illustrates the factory-installed hot gas bypass(HGBP) option for 38AUD units. See Fig. 34 for the locationof the Hot Gas Bypass. The HGBP is set at about 109 psig(752 kPa) (about 36°F (2°C) saturation temperature), tomaintain the evaporator coil temperatures above 36°F (2°C).The liquid injection valve (TXV) is set at approximately 17°F(9°C) superheat. The valves on the HGBP option are preset atthe factory, but may be adjusted in the field.As the load on the indoor evaporator decreases, the suctionpressure will decrease which is detected by the HGBP valve(constant pressure valve). When the suction pressure approach-es 109 psig (752 kPa), the HGBP valve begins to open to allowhot gas from the compressor to bypass to the suction pipe in acontrolled manner to attempt to maintain a constant suctionpressure. Since hot gas is too hot for entering the compressor,the device includes a liquid injector (or TXV) which feeds a lit-tle refrigerant from the liquid line through the TXV to de-su-perheat the hot gas and maintain an acceptable refrigerant qual-ity to not damage the compressor. When hot gas bypasses, it re-duces the mass flow of refrigerant to the evaporator whichreduces its capacity, and attempts to maintain the suction satu-ration temperature above 32°F (0°C) which minimizes the po-tential for freeze-up in the evaporator coil.The HGBP solenoid valve, as indicated in the lower leftof Fig. 33, allows HGBP control during first stage coolingoperation.