Loading ...
Loading ...
Loading ...
I Combination Units Installation InstructionsI
7. Economizer
The purpose of an economizer is to: economizers or on the actuator motor of three-position
economizers.
• Provide cool outside air to the conditioned space dur-
ing the cooling cycle to minimize the use of the com-
pressors.
• Bring outside air into the conditioned space to meet
minimum fresh air requirements whenever the circula-
tion blower is running.
Figure 16 Downflow Economizer 1
Theoryof Operation
The economizer has two sets of dampers that are mechani-
cally linked together. The fresh air dampers regulate the in-
take of outside air and the return air dampers regulate the
flow of return air (see Figure 16). When the fresh air damp-
ers modulate open, the linkage causes the return air damp-
ers to modulate closed.
The economizer is controlled by a logic module which field
connects to the unit controls through a plug harness. The
logic module also controls the compressor staging based on
the thermostat input.
The minimum opening position of the fresh air dampers is
field adjustable. It is set on the logic module of modulating
The enthalpy sensor is factory installed on the fresh air
dampers of the economizer. The enthalpy change-over
point is adjustable on the logic module.
A discharge air sensor is field installed in the blower inlet.
The discharge air sensor keeps the discharge air above
56°F (13.3°O).
A positive pressure is created when the fresh air dampers
open and the return dampers close. This pressure must be
vented or the air will not circulate properly. This is the func-
tion of the barometric relief damper. A positive pressure
forces thebarometric relief damper to swing open.
The fresh air dampers open to the minimum position for out-
side air whenever the circulation blower is ON.
When the thermostat is in the FAN AUTO position, the fresh
air dampers will close completely whenever heating or cool-
ing is not called for.
If Using a2- StageThermostat
On a call for cooling, ifthe economizer outdoor air sensor de-
termines that the outside air is cool enough (and in the case
of an enthalpy sensor, dry enough), the fresh air dampers
will modulate open and the return air dampers will modulate
closed.
If the conditioned space is not being maintained at the se-
lected temperature, the thermostat will make Y2 and call for
second stage cooling by energizing the economizer logic
module at the low voltage terminal board. This energizes Y1
and contactor which energizes the condenser fan and com-
pressor for cooling to assist the economizer.
NOTE FOR 6-1/3 UNITS ONLY: Contactor C2 cannot be
energized to operate compressor 2 while the economizer is
still energized since Circuit 1 is activating the economizer
and Circuit 2 is activating compressor 1.
If the thermostat is still calling for cooling and the outside air
warms to above the setting for economizer operation:
A. The economizer dampers will close to the minimum
position for outside air and remain there.
B. Contactor Cl will remain energized and compressor 1
will continue to run.
C. Conctactor C2 will close and compressor 2 will start.
If Using a Single-Stage Thermostat
When using a single stage thermostat, all steps as outlined
above will be followed with the exception of the following:
The compressor will only be energized when the outside air
reaches a temperature above the preset limit of the econo-
mizer. When ambient conditions are NOT suitable for econo-
mizer operation, ONLY the compressor will run, and the
economizer will NOT be energized.
513 01 1002 00 _f_
Loading ...
Loading ...
Loading ...