Bryant SM03-4 Service Manual page 49

TABLE 12—TROUBLESHOOTING VOLTAGE READINGS AND TEST POINTS
LOCATION
L1 and L2
L3 and L4
9-pin connector
7 and 9
T1 and T3
SEC1 and SEC2
R and C
G and C
Y and C
O and C
W2T and C
W2D and C
LOCATION
HI and F1
LO and F1
Y and C
o
9-pin connector
1 and 4
9-pin connector
2 and 4
9-pin connector
3 and 4
vac—volts AC
vdc—volts DC
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.
INPUT VOLTAGES
NORMAL READING
208/230 vac Main power supply input to fan coil
208/230 vac Power to electric heaters
208/230 vac Power to smart control
208/230 vac Power to transformer
24 vac Power from transformer secondary
24 vac Power from transformer secondary
24 vac Call for continuous fan signal from room thermostat
24 vac Call for heat/cool signal from room thermostat
Signal to energize reversing valve from room thermostat (cooling). Also present
24 vac
during defrost.
24 vac Call for electric heat from room thermostat
24 vac Defrost initiation signal from heat pump
OUTPUT VOLTAGES
NORMAL READING
208/230 vac
208/230 vac
24 vac
24 vdc
24 vdc
24 vdc
PURPOSE
Power to blower motor (high speed)
Power to blower motor (low speed)
Power to energize contactor in heat pump (heat and cool modes)
Power to energize SEQ 1
NOTE: Sequencers use DC voltage
Power to energize SEQ 2
Power to energize SEQ 3
• Is LED flashing appropriate code for number of
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?
F. Checking Sequencer Operation
To check for operation of power circuit of sequencer/relay, place
voltmeter leads
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.
G. 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.
—49—
PURPOSE
across sequencer/relay terminal 4 of