When the control determines that the outdoor air is suitable, the first stage of cooling is always free cooling.
If the parameter all compressors off in free cooling is on, free cooling is used regardless of the number of cooling stages demanded.
Cooling stages set to one for single compressor unit
With a stage 1 cooling demand (Y1 input), the economizer modulates to get SAT to VAV cooling supply air temperature upper setpoint +/-5°F. If the Y1 input remains on for 20 minutes, the C1 output energizes and the economizer opens to 100%.
With stage 2 cooling demand (Y2 input) and the Y1 input has been present less than 20 minutes, then the economizer opens to 100%.
If the Y1 or Y2 has been present for more than 20 minutes, then the C1 output energizes.
Cooling stages set to two for a two compressor unit
With a stage 1 cooling demand (Y1 input), the economizer modulates to get the SAT to the VAV cooling supply air temperature upper setpoint +/-5°F.
With a stage 2 cooling demand (Y2 input), the economizer modulates to 100% and energizes one compressor output. After 20 minutes, the second compressor output energizes.
When the Y2 stage 2 cooling demand is removed, all compressor outputs are de-energized and the economizer modulates to get the SAT to the upper SAT setpoint +/-5°F.
Cooling stages set to four for a four compressor unit
With a stage 1 cooling demand (Y1 input), the economizer modulates to get the SAT to the upper SAT setpoint +/-5°F.
With a stage 2 cooling demand (Y2 input), the economizer opens to 100% and the first compressor output energizes.
With a stage 3 cooling demand (Y3 input), a second compressor output energizes.
With a stage 4 cooling demand (Y4 input), a third compressor output energizes and 20 minutes after the Y4 input the fourth compressor output energizes.
When each cooling demand is removed, the compressor outputs de-energize in reverse order without time delays. When only a Y1 input remains, the economizer controls the SAT to the upper SAT setpoint +/- 5°F.