Bryant FA4A - Manual (Page 4)

A U G / 1 4 / 2 0 0 8 / T H U 0 3 : 4 5 UTC TECH PUB F A X N o , 3 1 7 2 4 0 5 6 6 2
PCB BLOCK WIRINS
LOW
VOLTAGE
FUSE
FIg. 3—Fan Còli
2. Functional Control
a. Thermostat and Relay Control
When thermostat calls for the fan in cooling, heat pomp,
heating, or fan-only mode, a 24-vdc signal is sent to
relay. This causes the relay to close its nonnally-opcn
contacts, turning On fan. When thermostat no longer calls
for the fan, the signal sent to relay is turned off and relay
opens causing fan to turn off after a 90-sec fan-off delay,
b. Sequencer Interlock
The fan will also Operate whenever there is a call for
electric heat, even if fan relay is nOt energized. This
happens because fan is interlocked with first stage of
electric heat through the normally-dosed contact of fan
relay.
NOTE: The fan interlock is only connected to first stage electric
heat W2, W3 and E do not contain an interlock with fan. See
outdoor thermostat Installation Instructions when electric heat
Staging is desired;
C. Electric Heat
When thermostat calls for electric heat, a 24-vac signal is sent to
PCB through WZ, causing first stage to turn on. W3 and E also
receive signal if wired in with WZ. The signal sent to WZ causes
J5r$t stage to turn on. If W3 and E arc not wired to W2, the
sequencers can be controlled individually to stage additional
electric heat. The sequence control is described in the following
Section;
1. W2
When thermostat sends a signal to WZ, a Z4-vac signal is
applied across sequencer number f, causing it to close after
a short delay. When sequencer number 1 closes, first stage
of electric heal is energized. In straight electric heat, fan is
also energized through the nonnally-doscd contacts of fan
relay. In cooling, heat pump, or manual fan mode, fan will
already be running since fan relay would have been
energized. When thermostat stops calling for electric heat,
the
24-'Vac signal to sequencer number 1 turns off and
sequencer opens after a delay of 60 to 90 sec. When
sequencer opens, first stage of heat turns off along with fan,
providing thermostat is not calling for the fan.
2. W3
When a signal is sent to W3, a 24-vaO Signal to sequencer
number 2 causes sequencer to dose, with Second stage of
electric heat turning on after a short delay. The 24-vac
A9434S
Printed-Circuit Boafd , 2
signal applied to sequencer number iJ chuses fan -tb;opkate.
Timing is Such that'sequchc'or liuinB'if FWiIf'iiirn:tii.h:'before
sequencer number 2. Whem, sigriifl to'WS' is turned off,
sequencer number 2 op,ens;;^^aiter a short 'delay. tf^.W^Z is also
satisfied, first stage of.,dectriC'heat and^-fimwiy ais^o tum
off, providing thermostat is not calling for the fan.
3, E ■'
When thermostat ..sends, a signal :iDrB^ ' a' 24-v~ac signalris sent
to sequencer number 3, The 24^Wc; sighhl' applied to
sequencer number 3 turns" on third'stagcof'clcctric heat.
The 24-vac signal applied to sequencer number 1 turns on
first stage of electric heat'arid fan. ’^hen 'thermostat stops
calling for electric heat,' the signartO'Sequ£d£efs I, 2, and 3
are turned off/^ahd sequdhfcefs b'|fieh;'''Th'il5''caii&es''dw^
heat to turn off with fan providihg'lheriniti^Iat'i^'hdt calling
for the fan,
^ ^ .
NOTE: Electric heaters are factory wired with alj stages tied
together. If independent staging is desired, cpnsul|, outdoor ther^
mostat Installation Instructions. ./
III. TROUBLESHOOTING PCB . ■ > 2
Use wiring schematic shown in Fig, 4 as a guide in troubleshooting
PCB unless otherwise notedv
■ ■ —
A. If Fan Will Not tum On ffom TherWost^i: ' ^
IF THERE IS NO HIGH VOLTAGE TO PCB:
1. Check plug/receptacle connection. This supplies power
from heaters to PCB. Be sure plug is connected properly.
, 2-, Check sequencer number X and plug wiring. Yellow, wire
should be connected to pin number 9 of plug and to limit
switch. Black wire should be Connected to pin number 7 of
plug and to sequencer number 1.
3. Check power leads Cl and L2. tf these are not receiving
power, system cannot function.
IF PCB HAS HIGH VOLTAGE APPLIED TO IT;
1, Check low-voltagc transformer leads R (red) and C
(brown). Be sure they are wired to correct locations,
2. Check output voltage of transformer secondary side R (red)
and C (brown). Be sure transformer output is between IS
and 30 vac. If transfbmicr output is incorrect and trans-
fonner is reqeiving correct input voltage (208v or 230v),
then transformer needs to be replaced with recommended
transformer. If no problem exists with transformer second-
ary, proceed to items 3 and 4.
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