Carrier 40GXC Service Manual

Also see for 38GXC: Installation instructions Owner's manual Owner's manual Product data

Contents

14Heating ModeIn this mode, the system heats the room air with the indoor fanrunning at either the selected speed or on Auto. As the coolingmode, the indoor fan will run continuously unless interrupted bythe cold blow algorithm. This algorithm will not allow the fan torun if the indoor coil temperature drops below a preset value.Compressor and fan operationAs shown below, the compressor and outdoor fan cycle on and offbased on the actual room temperature versus the set point. Theoutdoor fan is de--energized 30 seconds after the compressor isde--energized. The reversing valve is energized in heating and willstay energized for 2 minutes after the compressor is de--energized.The reversing valve is energized 2 seconds before the compressoris energized.CompressorOutdoor FanIndoor FanReversing ValveTS + 3.6°FTS + 9°FTS + 9°FTS + 3.6°F30 S≥ 3 minutes2 SCompressormatches loadCold Blowprevention2 minutesA09252Fig. 20 – Heat ModeIndoor Fan Operation – HeatingWhen in heating mode, as long as the coil temperature is above thethreshold for cold blow prevention, the fan runs continuouslyeither at the chosen set speed, or in Auto mode, where the speed isdetermined by the microprocessor based on the difference betweenthe room temperature and the temperature set point as shownbelow:TS + 5.4°FMediumLowHighTS + 1.8°FA09254Fig. 21 – Auto Fan -- Heat ModeCold Blow PreventionThis function prevents the cold air from blowing into a space whenin heat mode. When there is a demand for heating one of thefollowing conditions occurs:S If the indoor coil temperature is < 106_F (41.1_C) andthe room temperature is < 75_F (23.4_C), there will be a3 minute time delay before the indoor fan runs at lowspeed for 5 minutes.S If the indoor coil temperature is ≥106_F (41.1_C) andthe room temperature is ≥75_F (23.4_C, the indoor fanwill run at low speed for 1 minute.After one of the above steps occur, the indoor fan speed will bedetermined as shown below:LowMediumHighUser selected100.4 °F 109.4 °FA09354Fig. 22 – Cold Blow PreventionDefrostDefrost is controlled by the microprocessor and will occur if theunit operated in the heating mode for at least 45 minutes and any ofthe conditions below lasted for more than 3 minutes.3223 41 °FOutdoor Temperature10.41421.228.4Coil Temperature3223 41 °FA09355Fig. 23 – DefrostThe defrost cycle will terminate 12 minutes after the initiation ofthe defrost cycle or when the coil temperature is ≥50_F (10_C).The defrost algorithm is shown below:Defrost Initiated Defrost TerminatedIndoor FanOutdoor FanReversing ValveCompressor75 S12 min or tubetemp ≥ 50°F25 HzCold BlowPreventionA09256Fig. 24 – Defrost (continued)38/40GXC(Q)