Minimum Positioner; Enthalpy Sensor; Mixed Air Sensor - Lennox CHA16 Service Manual

If the enthalpy control is set at setpoint A" as shown in
figure 45, the following situation could occur.A cooling
demand when the outside air is at 75 and 20 percent
humidity would drive the economizer outdoor air
dampers open to utilize outdoor air for cooling.The
compressor cooling circuit would be disabled.Howev
er, if the outdoor air should change to 70 F (a drop in
temperature) and 70 percent humidity (a dramatic rise
in humidity), the total heat content" of the outdoor air
would rise above the enthalpy control setpoint and de-
activate the damper motor to the preset minimum posi
tion.If cooling demand is still present when the total
heat of the outside air rises above the control setpoint,
cooling demand is routed from the economizer to the
compressor cooling circuit.
Page 44