Installation guide

_Installation Instructions
6. Economizer Accessory
Single Package Air Conditioners I
The purpose of an economizer is to:
• Provide cool outdoor air to the conditioned space
during the cooling cycle to minimize the use of com-
pressors.
• Bring outdoor air into the conditioned space to meet
minimum ventilation air requirements whenever the
circulation blower is running.
Theory of Operation
The economizer has two sets of dampers that are mechan-
ically linked together. The outdoor air dampers regulate the
intake of outdoor air and the return air dampers regulate
the flow of return air (see FIGURE 6). When the outdoor air
dampers modulate open, the linkage causes the return air
dampers to modulate closed. A barometric relief damper is
installed in the return air side of the system. It relieves any
positive pressure in the unit created by the economizer.
The economizer is controlled by a logic module which field
connects to the unit controls through a harness plug. The
logic module also controls the compressor staging based
on the thermostat input.
FIGURE 6
[
Typical Downflow Economizer
Outdoor Air
Dampers
MixedAir
Sensor
Actuator Motor and
Logic Module
Return Air
Dampers
Sequence of Operation
NOTE: For correct wiring to the low voltage terminal board,
see the connection wiring diagram in the economizer's
documentation.
When a field supplied two stage thermostat is in the FAN
ON position:
1.
2.
The outdoor air dampers will open to the minimum
position for outdoor air.
On the thermostat's call for cooling, the thermostat
completes Circuit 1 between thermostat terminals R
and G and Y1 for first stage cooling.
If the economizer's enthalpy sensor determines that
the outdoor air conditions are below the setting for
economizer operation, the outdoor air dampers will
modulate open and the return air dampers will modu-
late closed.
.
4,
NOTE: All circuits have a low voltage safety circuit
consisting of a high pressure switch, a low pressure
switch and an anti-cycle delay timer.
The mixed air sensor at the blower inlet modulates
the economizer dampers to prevent the mixed air
from falling below 56°F (13.3°C). (Mixed air refers to
return air after it combines with outdoor air from the
economizer.) The mixed air sensor modulates the
outdoor air dampers between the full open and mini-
mum outdoor air positions.
If the mixed air is not cold enough to maintain the
conditioned space at the selected temperature, the
thermostat will make Y2 and call for second stage
cooling by energizing the economizer logic module.
This energizes the Y1 anti-cycle delay timer and
contactor Cl which energizes the condenser fan and
the compressor.
If the thermostat is still calling for cooling and the
economizer's enthalpy sensor determines that the
outdoor air conditions have risen above the setting
for economizer operation:
a. The economizer dampers will close to the mini-
mum position for outdoor air and remain there.
b. Contactor Cl will remain energized and the com-
pressor will continue to run.