Bryant SM03-4 Service Manual page 18

A. If the fan will not turn on from the thermostat:
IF THERE IS NO HIGH VOLTAGE TO THE PCB:
1. Check the plug/receptacle connection; this brings power to
the PCB. Make sure the plug is connected properly.
2. Check sequencer number 1 and the plug's wiring; the
yellow wire should be connected to pin number 9 of the
plug and the limit switch. A black wire should be connected
to pin number 7 of the plug and to sequencer number 1.
3. Check power leads L1 and L2. If these are not receiving
power, the system cannot function.
IF THE PCB HAS HIGH VOLTAGE APPLIED TO IT:
1. Check the low-voltage transformer leads, R and C. Make
sure they are wired to the correct locations. Note that
Fig. 13 shows wiring of the HK61GA001 board.
2. Check the output voltage of the secondary side, R and C, of
the transformer. If the circuit board is a HK61GA003, make
sure the ground strap is in place from C to the bracket. This
strap must be in place to complete the 24-v circuit. Make
sure the transformer output is around 24-v ac. If the
transformer output is zero-v ac and the transformer is
receiving the correct input voltage (208-v or 240-v), then
the transformer needs to be replaced with the recommended
transformer. If the transformer output is 24-v ac, then
proceed to 3 and 4.
3. Check the low-voltage fuse shown in Fig. 6 and Fig. 7. If
the fuse is blown, replace it. The transformer cannot supply
power to the board with the fuse blown or loose. If the fuse
blows when the unit has power applied to it, the system
most likely has 1 of the following problems:
a. If the transformer is shorting out, check the wiring of the
transformer.
b. The maximum load on the transformer is 40 VA. If the
load on the transformer is excessive, the low-voltage,
5-amp fuse will blow to protect the transformer. If the
load exceeds the VA rating of the transformer, a larger
VA rated transformer needs to be installed. Check the
sequencers for excessive current draw.
c. Check the wiring of the heaters. If the heater is miswired,
the fuse may blow. Check the diodes shown in Fig. 14
for signs of overheating. If the heater is miswired,
correct the miswiring.
4. Check the T1, T2, and T3 connections on the primary side
of the transformer. If they are not connected properly, the
low-voltage terminal board cannot supply the 24-v signal to
energize the fan relay. If the transformer is receiving the
correct primary voltage but is not outputting the correct
secondary voltage, the transformer needs to be replaced.
B. If the electric heat stages will not turn on but the fan
will turn on:
1. Check the wiring of the sequencer. Pay particular attention
to the high and low-voltage wiring of the sequencers.
2. Check the plug wiring to make sure that it is wired
correctly.
3. Check the voltage to the sequencer; sequencer number 1
receives a 24-vac signal. If it is receiving the correct
voltage, check to see if the sequencer is closing. If the
sequencer is not closing but is receiving the correct voltage,
replace the sequencer. If the sequencer is closing, check the
high-voltage wiring as discussed in 1 and 2.
C. If the electric heat and the fan will not turn on:
IF THERE IS NO HIGH VOLTAGE TO THE PCB:
1. Check the plug connection. This brings power to the PCB
transformer and the fan. Make sure the plug is connected
properly.
2. Check sequencer number 1 and the plug wiring. The yellow
wire should be connected to pin number 9 of the plug and
the limit switch. The black wire should be connected to pin
number 7 of the plug and to sequencer number 1.
3. Check incoming high-voltage power leads. If these are not
receiving power, the system cannot function.
IF THE PCB HAS HIGH-VOLTAGE APPLIED TO IT:
1. Check the low-voltage transformer leads, R and C. Make
sure they are wired to the correct location. The unit will not
function without proper connections.
2. Check the output voltage of the secondary side, R and C, of
the transformer. If the circuit board is an HK61GA003,
make sure the ground strap is in place from C to the bracket.
This strap must be in place to complete the 24-v circuit. If
the transformer output is zero-v ac, refer to "If the PCB has
high voltage applied to it" in column 1, numbers 3 and 4.
D. If the traces are burnt off the back of the PCB:
Usually whenever there is a trace blown on the PCB it means
either there has been a high-voltage short or high voltage has been
applied to the low-voltage circuit. This can be prevented by
making sure the PCB is wired correctly before the PCB has power
applied to it.
E. If there are blown diodes:
1. If diodes a and b are blown, it is probable the electric heater
plug was miswired. Correct the miswiring. It should be
noted the board will need to be replaced if the diode
indicated is bad.
2. If any of the c diodes are blown, the fan is miswired to 1 of
the low-voltage terminals, AUX1 or AUX2. Check to make
sure that the fan leads are connected to the proper terminals
as shown in Fig. 13. If the fan is connected properly, make
sure that no other high voltage is applied to the AUX
terminals.
F. The PCB fuse keeps blowing:
When the low-voltage fuse blows, it means the transformer would
have just blown if the fuse had not been in the circuit to protect it.
The fuse usually blows when there is a high current draw on the
transformer, high voltage applied to the low-voltage circuit, or a
direct secondary short. When there is a high current draw on the
transformer, it is most likely because the transformer has been
shorted or the system is trying to draw more VA than the
transformer is rated for. When the fuse blows because of high
voltage, the system has mixed high- and low-voltage signals.
1. Check the transformer and thermostat wiring as shown in
Fig. 11. Make sure the transformer is not shorting out by the
thermostat wires being miswired.
2. Check the wiring of the sequencers as shown in Fig. 13.
Make sure the low-voltage and the high-voltage wiring are
connected to the proper sequencers.
3. Check the VA draw on the transformer. If the VA draw is
more than the VA rating of the transformer, the fuse will
blow. If this is the case, replace the transformer with 1 that
has a higher VA rating and meets system specifications.
G. The fan runs continuously:
1. If the PCB has no low-voltage power, check the blue and
black fan leads. These may be switched at the sequencer.
2. If the PCB has low-voltage power, check the fan relay to
see if it is opening and closing. It may be stuck in the
normally closed position due to debris in the relay.
3. See Service Manager Bulletin (SMB) 92-3.
H. Transformer failure:
1. Check the 208-v and 240-v taps connected to T1, and T3.
They may be miswired.
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