46 WGZ030D through WGZ200D OMM 1130
If Unit Mode = Heat AND
At least one compressor is running AND
LWT error > 0.5 * Control band AND
Pulldown rate <= Max pulldown rate AND
Compressors running < unit capacity limit AND
Stage up timer expired THEN
Stage Up Now = True
Stage Down Now
The Stage Down Now flag is set based on the following tests:
If Unit Mode = Cool AND
LWT error < -0.5 * Control band AND
More than one compressor running AND
Stage down timer expired THEN
Stage Down Now = True
If Unit Mode = Cool AND
LWT error < (-0.5 * Control band - stop delta) AND
One compressor running AND
Stage down timer expired THEN
Stage Down Now = True
If Unit Mode = Cool AND
Number of compressors running > Demand limit AND
Stage down timer expired THEN
Stage Down Now = True
If Unit Mode = Heat AND
LWT error < -0.5 * Control band AND
More than one compressor running AND
Stage down timer expired THEN
Stage Down Now = True
If Unit Mode = Heat AND
LWT error < (-0.5 * Control band - stop delta) AND
One compressor running AND
Stage down timer expired THEN
Stage Down Now = True
Compressor Sequencing
Compressor staging is based primarily on compressor run hours and starts. Compressors that have less
starts will normally start before those with more starts. Compressors that have more run hours will
normally shut off before those with less run hours. In the event of a tie on number of starts, the lower
numbered compressor starts first. In the event of a tie on run hours, the lower numbered compressor shuts
off first. Run hours are compared in terms of tens of hours.
If possible, only one compressor per circuit will start before starting the second compressor on any
circuit. If a circuit is unavailable for any reason, the other circuit shall be allowed to stage the second
compressor on. When staging down, one compressor on each circuit shall be left on until each circuit has
only one compressor running.
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