Carrier MODU-PAC 50DF - Manual (Page 16)

Typical piping and wiring
CONTROL BOX itt
Controls
Operating sequence with economizer — (With­
out energy management Option/Accessory) using
thermostat with subbase.
Cooling
System switch set at AUTO, or COOL, indoor air fan runs
continually. Thermostat set at desired setting.
When thermostat calls for cooling and outdoor air
enthalpy is below setting of enthalpy controller, economizer
modulates open. (If outdoor air enthalpy is above enthalpy
set point, economizer remains at the minimum position.)
Economizer acts as first stage of cooling, providing “free
cooling” with outside air. If outside air alone cannot satisfy
the cooling requirements of the conditioned space, econo­
mizer cooling is integrated with mechanical cooling.
Compressor(s), working simultaneously with econo­
mizer, will be staged on to meet cooling load.
As conditioned space temperature approaches thermo­
stat’s cooling set point, stages cycle off, last stage first.
After all stages of mechanical cooling 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
the minimum position. At 50 F, economizer will be at the
minimum position.
Heating
System switch set at HEAT and AUTO., thermostat set
at desired setting. When thermostat calls for heating, one or
2 stages of heat energize to satisfy the heating demand.
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