Bryant SM03-4 Service Manual page 6

2. Check sequencer/relay number 1 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/relay number 1.
3. Check field power leads L1 and L2. If these are not
receiving power, system cannot function.
IF TRANSFORMER HAS HIGH VOLTAGE APPLIED TO IT:
1. Check low-voltage 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 18
and 30 vac. If transformer output is incorrect and trans-
former is receiving 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.
3. Check low-voltage fuse shown in Fig. 3A. If fuse is blown,
replace it with an identical 5-amp fuse. The transformer
cannot supply power to board with fuse blown or loose. If
fuse blows when unit has power applied to it, the system
most likely has 1 of the following problems:
a. Check all 24-v wiring for an electrical short.
b. The maximum load on transformer is 40 VA. If load on
transformer is excessive, the low-voltage 5-amp fuse
will blow to protect transformer. If load exceeds VA
rating of transformer, a larger VA rated transformer
needs to be installed. Check sequencers/relays for exces-
sive current draw.
c. Check wiring of heaters. If a heater is miswired, fuse
may blow. If a heater is miswired, correct miswiring by
comparing it to heater wiring label.
4. Check connections on primary side of transformer. If they
are not connected properly, the transformer secondary
SPT
FAN
RELAY
FF1D CONTROL BOX
FF1A/FF1B/FF1C CONTROL BOX
Fig. 3C—Electric Heater Control Boxes
B. If Electric Heat Stages Will Not Turn On But Fan Will
Turn On:
IF THERE IS NO HIGH VOLTAGE TO TRANSFORMER:
IF TRANSFORMER HAS HIGH VOLTAGE APPLIED TO IT:
IF TRACES ARE OVERHEATED ON BACK OF PCB:
Usually whenever a trace is blown on PCB, it means either there
has been a high-voltage short or high voltage has been applied to
low-voltage circuit. This can be prevented by making sure PCB is
wired correctly before PCB has power applied to it.
C. If Transformer Fuse Keeps Blowing:
When low-voltage fuse blows, it means transformer would have
blown if fuse had not been in circuit to protect it. The fuse usually
blows when there is a high current draw on transformer, high
—6—
5
cannot supply the 24-v signal to energize fan relay. If
transformer is receiving correct primary voltage but is not
putting out correct secondary voltage, transformer needs to
be replaced.
1. Check plug connection between heaters and board. This
supplies power to transformer and fan. Be sure plug is
connected properly.
2. Check sequencer/relay number 1 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/relay number 1.
3. Check incoming high-voltage power leads. If these are not
receiving power, system cannot function.
1. Check low-voltage transformer leads R (red) and C
(brown). Make sure they are wired to correct location. The
unit will not function without proper connections.
2. Check output voltage of transformer secondary side R (red)
and C (brown). If transformer output is low (less than 18
vac), refer to items 3 and 4 of previous "If Transformer Has
High Voltage Applied To It" section.
WARNING
ELECTRIC SHOCK
HAZARD
DISCONNECT
REMOTE POWER
SUPPLY BEFORE
OPENING PANEL.
PULL TO OPEN
322861-101 REV. A
WARNING
ELECTRIC SHOCK
HAZARD
DISCONNECT
REMOTE POWER
SUPPLY BEFORE
OPENING PANEL.
PULL TO OPEN
322861-101 REV. A
A98184