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Stage 1 Heating (both compressors run on 8−14 systems.
The 04−07 systems have only one compressor).
Auxiliary (Electric) Heat control — The 50TCQ unit
can be equipped with one or two auxiliary electric heaters,
to provide a second stage of heating. The DFB will
energize this Heating System for a Stage 2 Heating
Command
(heaters
operate
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).
Defrost — The defrost control mode is a time/temperature
sequence.
There
are
two
continuous run period and the test/defrost cycle period.
The temperature component is provided by Defrost
Thermostat 1 and 2 (DFT1 and DFT2 (A08−D09 only)
mounted on the outdoor coil.
The continuous run period is a fixed time period between
the end of the last defrost cycle (or start of the current
Heating cycle) during which no defrost will be permitted.
This period can be set at 30, 60, 90 or 120 minutes by
changing the positions of DIP switches SW1 and SW2
(see Fig. 35 and Table 9). The default run periods are 60
minutes for unit sizes 04−06, 30 minutes for unit size 07,
90 minutes for unit sizes 08−09 and 60 minutes for unit
sizes 12−14.
Fig. 35 − DIP Switch Settings — Defrost Board
At the end of the continuous run period, the defrost
control will test for a need to defrost. On unit sizes 04−07
(single compressor designs), DFT1 controls the start and
termination of the defrost cycle. If DFT1 is still open, the
defrost test/run window is closed and the control repeats
the continuous run period. If DFT1 is closed, the defrost
cycle is initiated. The defrost period will end when DFT1
opens (indicating the outdoor coil has been cleared of
frost and ice) or a 10 minute elapsed period expires,
whichever comes first.
On unit sizes 08 and 14 (two circuit designs), DFT2
(located on the bottom circuit of the outdoor coil on the
08−09 size and the outdoor coil with two bends on the
12−14 sizes) controls the start and termination of the
defrost cycle. If DFT2 is still open, the defrost test/run
window is closed and the control repeats the continuous
run period. If DFT2 is closed, the defrost cycle is initiated
in Circuit 2. The defrost period will end when DFT2
opens (indicating the outdoor coil has been cleared of
concurrently
with
time
components:
The
C09283
frost and ice) or a 10 minute elapsed period expires,
whichever comes first.
On sizes 08−14, Circuit 1's defrost thermostat DFT1
(located on the upper circuit of the outdoor coil on 08−09
size and the outdoor coil with one bend on the 12−14
sizes.) cannot initiate a unit defrost cycle; only DFT2 can
do this. But once Circuit 2 is in defrost, the DFB will
monitor the status of DFT1. If DFT1 closes during a
Circuit 2 defrost cycle, Circuit 1 will also enter a defrost
cycle. Circuit 1's defrost cycle will end when DFT1 opens
(indicating the upper portion of the outdoor coil is cleared
of frost and ice) or the Circuit 2 defrost cycle is
terminated.
At the end of the unit defrost cycle, the unit will be
returned to Heating cycle for a full continuous run period.
If the space heating load is satisfied and compressor
operation is terminated, the defrost control will remember
where the run period was interrupted. On restart in
Heating, the defrost control will resume unit operation at
the point in the run period where it was last operating.
Defrost Thermostats — These are temperature switches
that monitor the surface temperature of the outdoor coil
circuits. These switches are mounted on the liquid tube
exiting the outdoor coil heating circuits. These switches
close on temperature drop at 30_F (−1_C) and reset open
on temperature rise at 80_F (27_C).
Indoor Fan Off Delay — The DFB can provide a 60 sec
delay on Indoor Fan Off if the thermostat's fan selector
switch is set on AUTO control. DIP Switch SW3 on the
DFB selects use of the fan off time delay feature. Setting
SW3 in the OPEN position turns the Fan Off Delay
feature on; setting SW3 in the CLOSED position disables
this feature. The delay period begins when Y1 demand or
W1 demand by the space thermostat is removed.
Defrost Speedup Functions — The DFB permits the
servicer to speed−up the defrost cycle. There are two
speed−up sequences: relative speed−up and an immediate
forced defrost. Speed−up sequences are initiated by
shorting jumper wires JMP17 and JMP18 together (see
Fig. 33); use a flat−blade screwdriver.
Shorting the jumpers for a period of 1 to 3 seconds
reduces the defrost timer periods by a factor of 0.1
sec/minute. (For example, the 90 minute run period is
reduced to 9 seconds) The DFB will step the unit through
a Heating cycle and a Defrost cycle using these reduced
time periods. This mode ends after the Defrost cycle.
27
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