Bryant SM03-4 Service Manual Download Page 48

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Troubleshooting Printed-Circuit Board

(Diagnostic LED)

The PCB of Smart Heat option heater package contains a micro-
processor which controls fan operation, fan speed, outdoor unit,
and heater elements. For troubleshooting, a service LED indicates
condition of PCB. See Table 11 for LED flash codes.

IV.

ELECTRICAL OPERATING SEQUENCES AND

TROUBLESHOOTING

NOTE:

Refer to Table 12 for proper input and output voltages.

See Fig. 40 for Smart Heat Proper Wiring Diagram.

Ready-To-Start

In ready-to-start (standby) mode, LED on board indicates a steady
flash.

In this mode, 24-v power should be available at control’s low
voltage terminal strip terminals R and C. If 24v is not present
across R and C, check the following:

• Is low-voltage fuse on control board good?

• Are line voltage fuses FU1 and FU2 good?

• Is LED on control on steadily or not on at all? Both of these

indications signal a possible board failure.

• Is 208/230-v power available to control across pins 7 and 9

of 9-pin connector? Is connection to board tight?

Continuous Fan

On a call for continuous fan, thermostat provides a 24-v input
signal to G terminal on low-voltage terminal strip. Sensing this
signal, the microprocessor energizes a relay on control to provide
power to high-speed winding of fan motor, at 1. The fan continues
to run until fan switch on thermostat is turned off.

During continuous fan operation with no call for heating or
cooling, LED indicates a steady flash, the same indication seen
when system is in standby.

The call for continuous fan operation signal can be checked by
placing voltmeter leads across terminals G and C of control’s
low-voltage terminal strip. If 24v is not seen across these termi-
nals, check for the following:

• Is 24v available across R and C? If not, refer to Ready-To-

Start section for items to check if 24v is not available.

• Is thermostat fan switch set for continuous operation?

Confirm fan operation. Voltage to operate fan can be confirmed by
placing voltmeter leads across terminals F1 and HI on control. The
reading should be 208/230v. If 208/230v is not observed, check the
following:

• Is 208/230v available at pins 7 and 9 of 9-pin connector? Is

connection to board tight?

• Are line voltage fuses FU1 and FU2 good?

If 208/230v is available across terminals F1 and HI and fan does
not operate, check the following:

• Is fan motor capacitor good?

• Is blower wheel jammed or loose? Are there any other

mechanical problems preventing fan operation?

Cooling

On a call for cooling, room thermostat provides input signals to
control board at terminals Y and O. The O signal is also available
to heat pump to energize reversing valve.

When it receives both these signals, the microprocessor responds
by providing a 24-v output signal at the Y

terminal. This output

signal energizes contactor in heat pump and starts compressor.
There is a 3 to 5 sec delay in output of Y

signal.

At the same time, control energizes fan coil’s fan motor on high
speed through terminals F1 and HI. The LED indicator on control
signals 5 flashes, indicating cooling operation.

The call for cooling signals can be confirmed by placing voltmeter
leads across low-voltage terminals Y, O, Y

, and C. The reading

should be 24v. If 24v is not available, check the following:

• Is 24v available across R and C? See Ready-To-Start section

for items to check if 24v is not available.

• Is thermostat function switch set in COOL position with

thermostat calling for cooling?

Assuming heat pump has power and is adequately charged, it
should be running at this time in cooling mode. Indoor fan should
also be running at this time. If indoor fan is not running, refer to
Continuous Fan section for items to check.

Heating (Compressor Only)

On a call for heat, room thermostat provides an input signal to
control board at terminal Y. This signal causes the microprocessor
to provide a 24-v output signal at terminal Y

to energize contactor

in heat pump. There is a 3 to 5 sec delay in output of Y

signal.

Thirty sec after Y is energized, control energizes fan motor. It may
run on high or low speed, depending on its operation in previous
cycle.

Compressor operation in current cycle is monitored by the smart
control to determine whether a fan speed change is required for
enhanced indoor comfort. The LED indicator on control signals 1
flash, indicating compressor operation only with no electric heat.

The call for heat signals can be confirmed by placing voltmeter
leads across low-voltage terminals Y, Y

, and C. The readings

should be 24v. If 24v is not available, check the following:

• Is 24v available across R and C? See Ready-To-Start section

for items to check if 24v is not available.

• Is thermostat function switch set in HEAT position with

thermostat calling for heat?

Assuming heat pump has power and is adequately charged, it
should be running at this time in heating mode. Indoor fan should
also be running at this time. If indoor fan is not running, refer to
Continuous Fan section for items to check. When room thermostat
is satisfied, indoor fan continues to run an additional 60 sec to
recover heat remaining in indoor coil.

Heating (Compressor and Electric Heat)

If heat pump alone cannot satisfy heat requirements of structure,
room thermostat calls for additional heat by way of an input to W2
terminal of control. When this occurs, control begins sequencing
on electric heaters by energizing the first sequencer/heat relay.
Indoor fan should be running at this time.

If room temperature requirements cannot be met, additional stages
of

electric

heat

are

energized

through

the

other

sequencers/relays, at 2.

TABLE 11—LED CODES FOR SMART HEAT PCB

FLASH CONDITION

INPUT SIGNALS