Carrier 48MA/50ME016-040 specifications Units with 2-ELEMENT Heaters, Units with 3-ELEMENT Heaters

HTR Ð Heater

*AFS1 deenergizes control circuit if loss of outdoor air occurs. ²Factory-supplied option.

Fig. 35 Ð Major Component Identi®cation (Typical 12-Zone Unit Shown).

When OAT is open, ®nal stage heating element in all zone modules is inactive. When OAT is closed, ®nal stage heating element in a zone module may be energized whenever second- stage thermostat for that zone module calls for heat as follows:

UNITS WITH 2-ELEMENT HEATERS

First-Stage Heat Ð One element energized

Second-Stage Heat

OAT Open Ð One element energized

OAT Closed Ð Two elements energized

UNITS WITH 3-ELEMENT HEATERS

First-Stage Heat Ð One element energized

Second-Stage Heat

OAT Open Ð Two elements energized

OAT Closed Ð Three elements energized

Optional Glycol Heating Coils Ð Start up glycol solution supply system in accordance with equipment manu- facturer's instructions. Solution supply temperature must not exceed 200 F. Maximum solution ¯ow through each zone module heating coil is 6 gpm.

Zone Air¯ow Adjustment Ð Adjust each zone duct balancing damper to provide required air¯ow to each zone. Increasing or decreasing air¯ow to one zone may cause a change in the air¯ow to other zones. After initial damper settings have been made, repeat the adjustment procedure, as required, to be sure ®nal desired air¯ows are achieved. Do not go below 600 cfm or above 1200 cfm per zone module.

Be sure that temperature rise is within range shown on unit instruction plate and Table 1 (48MA only).

Sequence of Operation Ð When unit power is on and no zone thermostat is calling for cooling or heating, the evaporator fan and crankcase heater(s) are on. The outdoor- air dampers are at the pre-set position.

COOLING Ð 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 in response 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 units only). If required, compressor no. 1 will unload when com- pressor no. 2 (024-040 units only) is energized. As cooling requirements decrease, capacity control pressurestats pre- vent compressor no. 1 from shutting down while compres- sor no. 2 (024-040 units only) is in operation. Compressor no. 1 will fully load up after compressor no. 2 (024-040 units only) 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 valve will meter hot gas to outdoor air evaporator coil to supply additional load. On 48MA and 50ME040, hot gas is intro- duced into evaporator whenever required to eliminate un- loader short-cycle operation.

The Motormaster head pressure control device will vary speed of condenser-fan motor no. 1 to regulate air¯ow across condenser coil. As required, condenser-fan motor no. 2 (no. 2 and 3 on 3-fan units) will cycle on and off in response to head pressure via a cycling pressurestat. See Head Pres- sure Control section on page 40.

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