Carrier 48MA/50ME016-040 Installation, Start-up And Service Instructions Manual

Contents

Carrier 48MA/50ME016-040 Installation, Start-up And Service Instructions Manual Manual pdf 38 page image

When OAT is open, final stage heating element in all zonemodules is inactive. When OAT is closed, final stage heatingelement in a zone module may be energized whenever second-stage thermostat for that zone module calls for heat asfollows:UNITS WITH 2-ELEMENT HEATERSFirst-Stage Heat — One element energizedSecond-Stage HeatOAT Open — One element energizedOAT Closed — Two elements energizedUNITS WITH 3-ELEMENT HEATERSFirst-Stage Heat — One element energizedSecond-Stage HeatOAT Open — Two elements energizedOAT Closed — Three elements energizedOptional Glycol Heating Coils — Start up glycolsolution supply system in accordance with equipment manu-facturer’s instructions. Solution supply temperature must notexceed 200 F. Maximum solution flow through each zonemodule heating coil is 6 gpm.Zone Airflow Adjustment — Adjust each zone ductbalancing damper to provide required airflow to each zone.Increasing or decreasing airflow to one zone may cause achange in the airflow to other zones. After initial dampersettings have been made, repeat the adjustment procedure,as required, to be sure final desired airflows are achieved.Do not go below 600 cfm or above 1200 cfm per zonemodule.Be sure that temperature rise is within range shown onunit instruction plate and Table 1 (48MA only).Sequence of Operation — When unit power is onand no zone thermostat is calling for cooling or heating, theevaporator fan and crankcase heater(s) are on. The outdoor-air dampers are at the pre-set position.COOLING — On a call for cooling from a zone thermostat,compressor no. 1, with unloader(s), starts; the liquid line so-lenoid for that zone evaporator coil opens; and condenser-fan motor no. 1 starts. Compressor will load or unload inresponse to suction pressure as required. As additional cool-ing is required (i.e., more zones call for cooling), compres-sor no. 2 (no unloaders) will be energized (024-040 unitsonly). If required, compressor no. 1 will unload when com-pressor no. 2 (024-040 units only) is energized. As coolingrequirements decrease, capacity control pressurestats pre-vent compressor no. 1 from shutting down while compres-sor no. 2 (024-040 units only) is in operation. Compressorno. 1 will fully load up after compressor no. 2 (024-040 unitsonly) shuts down as required to match heat load.If heat load is not sufficient to maintain operation of com-pressor no. 1 in an unloaded condition, hot gas bypass valvewill meter hot gas to outdoor air evaporator coil to supplyadditional load. On 48MA and 50ME040, hot gas is intro-duced into evaporator whenever required to eliminate un-loader short-cycle operation.The Motormastert head pressure control device will varyspeed of condenser-fan motor no. 1 to regulate airflow acrosscondenser coil. As required, condenser-fan motor no. 2(no. 2 and 3 on 3-fan units) will cycle on and off in responseto head pressure via a cycling pressurestat. See Head Pres-sure Control section on page 40.HTR — Heater*AFS1 deenergizes control circuit if loss of outdoor air occurs.†Factory-supplied option.Fig. 35 — Major Component Identification (Typical 12-Zone Unit Shown).38