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Fig. 35 — Defrost Control Board Arrangement
DIP
SWITCHES
SPEED-UP
JUMPERS
Fig. 36 — Defrost Control Board Location
20
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 the defrost cycle and de-energized during heating cy-
cles. Once energized at the start of a cooling stage, the reversing
valve will remain energized until the next heating cycle demand is
received. Once de-energized at the start of a Heating cycle, the re-
versing valves will remain de-energized until the next cooling
stage is initiated.
Compressor control
The DFB receives inputs indicating Stage 1 Cooling, Stage 2
Cooling and Stage 1 Heating from the space thermostat or unit
control system (PremierLink™ controller or RTU Open control-
ler); it generates commands to start compressors with or without
reversing valve operation to produce Stage 1 Cooling (one com-
pressor runs), Stage 2 Cooling (both compressors run) or Stage 1
Heating (both compressors run).
Auxiliary (Electric) Heat control
The 50HCQ unit can be equipped with one or two auxiliary elec-
tric heaters, to provide a second stage of heating. The DFB will
energize this Heating System for a Stage 2 Heating Command
(heaters operate concurrently with compressor(s) in the Stage 1
Heating cycle), for an Emergency Heating sequence (compressors
are off and only the electric heaters are energized) and also during
the Defrost cycle (to eliminate a "cold blow" condition in the
space).
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