Bryant SM03-4 Service Manual Download Page 49

Page: 49 / 52

The logic of control determines how much and how soon these
additional stages are brought on. By observing LED status light,
the number of operating stages of electric heat can be determined.
The control also varies indoor fan speed depending on number of
energized stages of heat. In general, the more stages of electric
heat, the higher the fan speed.

There is no hard and fast rule for determining exactly when stages
will be energized since microprocessor in the smart control
constantly monitors duration of previous heating cycle, setting of
room thermostat, and number of stages of heat needed in previous
cycle to satisfy room thermostat. Rather than try to determine what
should be operating when, service technicians should check LED
status light to see how many stages of electric heat are energized
at a given time and confirm operation of sequencer/relay using a
voltmeter. If a quick check of all stages is desired, set room
thermostat as high as it will go. With a constant signal on W2T
terminal, sequencers/relays energize every 10 minutes until all
heaters are on.

The previous paragraphs described how to check for low-voltage
inputs to control by placing voltmeter leads across low-voltage
terminal strip and checking for 24v. The call for electric heat can
be confirmed by placing voltmeter leads across W2T and C.

To check for operation of sequencers/relays, check directly across
appropriate coil for 24 volts DC.

NOTE:

All sequencer/relay coils are powered by 24 volts DC.

This voltage is generated internally by the smart control.

In this example, sequencer/relay 1 is being checked. The procedure
is the same for all other sequencers/relays. If 24 volts DC is not
observed, check the following:

• Is room thermostat calling for electric heat? This can be

confirmed by checking for 24 volts AC between low-voltage
terminal strip terminals W2T and C.

• Is

LED

flashing

appropriate

code

for

number

sequencers/relays energized? In this example, 2 flashes should be
visible, indicating 1 sequencer/relay is energized. Indicator tells
how many sequencers/relays are energized, but does not tell which
ones are.

• Is 9-pin connector for heater package tightly secured to

control board?

Checking Sequencer Operation

To check for operation of power circuit of sequencer/relay, place
voltmeter

leads

across

sequencer/relay

terminal

sequencer/relay 1 and terminal 4 of limit switch 3. The reading
should be 208/230v, and heater should be energized.
If 208/230v is not observed at terminals specified, check the
following:

• Are fuses FU3 and FU4 good?
• Is limit switch LS3 open? If so, check fan coil air filter or air

distribution system for blocking or restriction that might reduce
airflow and cause limit switch to open.
Operation of heaters can be confirmed further by using a clamp-on
ammeter in circuit shown to verify current is flowing through
heaters. Amperage readings will depend on size of heater. The
procedure for checking other sequencers/relays in system is
identical to that just described.

Emergency Heat

Emergency heat mode requires that room thermostat be placed in
EMERGENCY HEAT position. This locks out and prevents
operation of heat pump outdoor unit. In this mode, heat is provided
exclusively by electrical heaters in fan coil.
In this mode, room thermostat, at 1, provides an emergency heat
input signal to smart control at terminal W2T. If jumper JW1, at 2,
has not been cut and an outdoor thermostat installed to control
electric heat stages, that same input signal is applied to terminal
W3. For this example, assume that jumper JW1 has not been cut.

TABLE 12—TROUBLESHOOTING VOLTAGE READINGS AND TEST POINTS

INPUT VOLTAGES

LOCATION

NORMAL READING

PURPOSE

L1 and L2

208/230 vac

Main power supply input to fan coil

L3 and L4

208/230 vac

Power to electric heaters

9-pin connector
7 and 9