78
38APS Units — On a call for cooling, the Indoor Fan Status
Cir A (Inputs
GEN.I
ID.F.A) is checked. The switch must
be closed before the capacity routine will start. The lead com-
pressor will be determined and started. See Circuit Compressor
Staging on page 112. If the lead compressor is a digital com-
pressor and is enabled, the compressor will start fully loaded
for 90 seconds prior to starting to cycle between loaded and un-
loaded.
The unit will stage compressors every 90 seconds to meet
the requested capacity. With every change in capacity that oc-
curs, a 90-second time delay is initiated and the capacity stage
is held during this time delay. If the capacity change is a change
of the digital compressor only, the compressor will be modulat-
ed to the requested capacity without moving in increments.
For example, if the requested capacity requires a change to the
compressor unload time from 8 to 2 seconds, that change will
occur without the intermediate steps of 7, 6, 5, 4, and 3
seconds. During operation, the controls will stage the condens-
er fans to maintain head pressure. See Head Pressure Control
on page 117.
As part of normal operation, if a single compressor operates
for the cumulative time of 60 minutes without an increase in
circuit capacity, an oil recovery routine is initiated. When this
routine is initiated, a second compressor in the circuit is started.
Once started, the normal capacity control routine takes priority
and will turn off the compressor if needed.
As the capacity requirement begins to decrease, the ma-
chine controls will reduce the unit’s capacity in response to the
requested capacity signal. If the unit is equipped with Mini-
mum Load Control, it will not be active until the unit is on its
last stage of capacity.
See Fig. 87-139 for capacity loading, C.TYP=7.
Fig. 87 — Capacity Loading, C.TYP=7
38APD,APS025-030, Non-Digital, Equal (Default) or Staged Circuit Loading,
Circuit A or B (38APD Only) Leads
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