Reversing Valve Control; Compressor Control - Carrier 38AUQ16-25 Installation, Start-Up And Service Instructions Manual

Fig. 23 — Field Wiring of Indoor Coil Freeze Protection Switch (FPT) (Dual Circuit Shown)
Fig. 24 — Defrost Control Board (DFB) Arrangement
LOC1
or
LPS1
HPS1 FPT1
CIRCUIT 1
HPS LPS FPT
CIRCUIT 2
HPS LPS FPT
HPS2 LOC2 FPT2
or
LPS2
DIP
Switches
Speed-Up
Jumpers
C1
NOTE: Move compressor contactor wire
from right-side LPS terminal
to right-side FPT terminal
C2

REVERSING VALVE CONTROL

The DFB has two outputs for unit reversing valve control. Opera-
tion of the reversing valves is based on internal logic; this applica-
tion does not use an "O" or "B" signal to determine reversing
valve position. Reversing valves are energized during the Cooling
stages and de-energized during Heating cycles. Once energized at
the start of a Cooling stage, the reversing valve will remain ener-
gized until the next Heating cycle demand is received. Once de-
energized at the start of a Heating cycle, the reversing valves will
remain de-energized until the next Cooling stage is initiated.

COMPRESSOR CONTROL

The DFB receives inputs indicating Stage 1 Cooling and Stage 1
Heating from the space thermostat or third-party Building Man-
agement System; it generates commands to start compressors with
or without reversing valve operation to produce Stage 1 Cooling
(one compressor), or Stage 1 Heating (both compressors run).
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