Carrier 48MA/50ME016-040 - Manual (Page 38)

When OAT is open, final stage heating element in all zone
modules is inactive. When OAT is closed, final 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 — One element energized
Second-Stage Heat
OAT Open — One element energized
OAT Closed — Two elements energized
UNITS WITH 3-ELEMENT HEATERS
First-Stage Heat — One element energized
Second-Stage Heat
OAT Open — Two elements energized
OAT Closed — Three elements energized
Optional Glycol Heating Coils — Start up glycol
solution supply system in accordance with equipment manu-
facturer’s instructions. Solution supply temperature must not
exceed 200 F. Maximum solution flow through each zone
module heating coil is 6 gpm.
Zone Airflow Adjustment — Adjust each zone duct
balancing damper to provide required airflow to each zone.
Increasing or decreasing airflow to one zone may cause a
change in the airflow to other zones. After initial damper
settings 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 zone
module.
Be sure that temperature rise is within range shown on
unit instruction plate and Table 1 (48MA only).
Sequence of Operation — 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 — 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 airflow 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.
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).
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