Optional Outdoor Air Cfm Control - Lennox LCH036 Installation Instructions Manual

Optional Outdoor Air CFM Control

Outdoor air CFM Control is a factory-installed option
available on units equipped with a supply air variable
frequency drive (VFD) and economizer.
The Unit Controller modulates outdoor air dampers to
maintain a constant amount of outdoor air regardless of
blower speed. This ensures minimum ventilation
requirements are met at lower supply air speeds.
The Unit Controller uses a velocity sensor (A24) to
modulate dampers. The sensor is located in the outdoor
air stream. See figure 34.
Set Damper Minimum Position
1- Operate unit at full supply air CFM with all zone
dampers open. Refer to VFD Supply Air Blower
Start-Up section in this manual.
2- Use an air flow hood to measure the outdoor air CFM
entering the unit.
3- Set economizer DIP switch to "DSET" position as
shown in figure 36. DIP switch is located on the A55
Unit Controller board. See figure 35.
4- Adjust the MIN POS SET potentiometer until the air
flow hood reads the design minimum outdoor air
CFM. See figure 36.
LED FLASHING GREEN
"HEARTBEAT" LED
INDICATES NORMAL
OPERATION
B C D
IN "ODE" MODE, SET ENTHALPY
CONTROL IN "A" POSITION. IF AIR
IS TOO HUMID, ROTATE CLOCK­
A DIF
ENTHALPY
WISE TO LOWER SETTING
SETPOINT
NOTE - Refer to local codes or authorities having
jurisdiction when determining design minimum outdoor
air requirements.
5- Return the economizer DIP switch to original
position. Refer to the Unit Controller manual.
ECONOMIZER SETTINGS
STEADY YELLOW "OUT­
DOOR AIR SUITABLE" LED
INDICATES OUTDOOR AIR IS
SUITABLE FOR COOLING
TMP GLO
GLO TMP
C
OPEN
D
B
A 0 100
DIF
ENTH. SET PT. MIN POS SET
0-100% MINIMUM
POSITION POTEN­
TIOMETER
FIGURE 35
Page 40
VELOCITY SENSOR LOCATION
FIGURE 34
A FLASHING YELLOW
OAS LED INDICATES THE
IAQ SENSOR IS REQUEST­
ING MORE FRESH AIR
DIP SWITCH SET
IN TMP, ODE, DIF
OR GLO MODE
OPEN
0
100
MIN POS
SET
A24
SENSOR
A24
CONTROL