Carrier 50DL - Manual (Page 12)

heating LED on the left-hand side of thermo­
stat or transmitter should begin to glow. Electric
heat should cycle on. Check supply duct outlets
for heat. If heating equipment does not cycle on,
see Service, Electronic Component Checkout.
4. Move the heating set point below room tempera­
ture. The heating equipment should cycle off and
the heating LED intensity should decrease to a
faint glow or go off completely.
5. Return the heating and cooling set points to
desired settings and lock in place. On standard
units, return subbase switch to desired position.
On units with Energy Management option, an
adjustable morning warmup thermostat is used
to hold dampers closed until return air reaches
the setting on the thermostat located in the
night setback box.
To Shut Off Unit — Standard units, set the subbase
selector switch to OFF or set the heating tempera­
ture selector lever below room temperature. For
units with Energy Management option, set the heat­
ing temperature selector switch below room
temperature.
AUTOMATIC CHANGEOVER — Standard units
automatically switch from heating to cooling mode
when the subbase selector switch is set at AUTO,
and the temperature of the conditioned space rises to
the cooling selector lever setting. When the tempera­
ture of conditioned space falls to heating selector
lever setting, the unit automatically changes from
cooling mode to heating mode.
The thermostat and unit are so connected that
cooling and heating systems do not operate
simultaneously.
On units with Energy Management option, with
dual set point thermostat or transmitter, changeover
is also automatic. There is a minimum 3 F deadband
between the heating and cooling set points.
ECONOMIZER OPERATION — If unit is
equipped with modulating outdoor air control
(economizer), set enthalpy control (Fig. 4 and 6) at
“A.” Unit capability to integrate economizer with
.mechanical cooling allows for a higher changeover
point than conventional economizer systems. Be­
cause of this, outside air is desired whenever its
enthalpy (total heat content) is below return air
enthalpy. Typical return air conditions, shaded
portion of Fig. 7, indicate that setting “A” should
be used for maximum operating economy.
OPERATING SEQUENCE WITH ECONO­
MIZER (without Energy Management option)
using thermostat with subbase.
Cooling — System switch set at AUTO, or COOL,
fan switch at ON or AUTO, (indoor air fan runs
intermittently). Thermostat set at desired setting.
When thermostat calls for cooling and outdoor
air enthalpy is below setting of enthalpy controller.
the economizer modulates open. (If outdoor air
enthalpy is above enthalpy set point, the outdoor
air dampers remain at minimum position.) Econo­
mizer acts as the first stage of cooling, providing
“free cooling” with outside air. If outside air alone
cannot satisfy the cooling requirements of condi­
tioned space, economizer cooling is integrated
with mechanical cooling.
Compressor(s), working simultaneously with
economizer, will come on in stages to meet the
cooling load.
As the conditioned space temperature approaches
the thermostat’s cooling set point, stages cycle off,
last stage first. After all stages of mechanical cool­
ing are off, economizer modulates to minimum
position.
During the cooling cycle, a discharge air sensor
senses discharge air temperature. If discharge air
temperature drops below 62 F, economizer starts
to modulate toward minimum position. At 50 F dis­
charge temperature, the economizer will be at mini­
mum position.
Heating — System switch set at HEAT or AUTO.,
fan switch at ON or AUTO., thermostat set at
desired setting. When thermostat calls for heating,
one or 2 stages of heat energize to satisfy heating
demand.
As space temperature approaches the heating
temperature set point, heating stages cycle off.
During heating, economizer is limited to the
minimum position to provide outdoor air for
ventilation requirements.
OPERATING SEQUENCE WITH ECONO­
MIZER AND ENERGY MANAGEMENT option
(using electronic thermostat or transmitter).
Clock in remote control box switches controls to
OCCUPIED mode. Indoor air fan runs continually
while in OCCUPIED mode.
If return air temperature is below the adjustable
setting of morning warmup thermostat, outdoor-
air dampers remain closed.
When return air temperature goes above setting
of morning warmup thermostat, economizer goes
to adjustable minimum position.
When thermostat calls for cooling and outdoor
air enthalpy is below setting of enthalpy controller,
economizer modulates open. (If outdoor air en­
thalpy is above enthalpy set point, economizer
remains at minimum position.) The economizer acts
as the first stage of cooling, providing “free cooling”
with outside air. If outside air alone cannot satisfy
cooling requirements of the conditioned space,
economizer cooling is integrated with mechanical
cooling.
Compressor(s), working simultaneously with
economizer, will come on in stages to meet the
cooling load.
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