Bryant Legacy 674D Installation Instructions Manual Download Page 18

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Gas Heating Fan Speed Set-up

To change the gas heating speed:

1. Remove the vinyl cap off of the desired speed tap wire

(Refer to Table 6 for color coding). Table 10 shows the
temperature rise associated with each fan speed for a given

static pressure. Make sure that the speed chosen delivers a
temperature rise within the rise range listed on the unit

rating plate.

2. Remove the current speed tap wire from the “GAS HEAT”

terminal on the interface fan board (IFB) (Fig.14) and place

vinyl cap over the connector on the wire.

3. Connect the desired speed tap wire to the “GAS HEAT”

terminal on the interface fan board (IFB).

Single Cooling Fan Speed Set-up (Dehumidification

feature not used)

To change cooling speed:

1. Remove the vinyl cap off of the desired speed tap wire

(Refer to Table 6 for color coding). Add the wet coil

pressure drop in Table 8 to the system static to determine the
correct cooling airflow speed in Table 10 that will deliver

the nominal cooling airflow as listed in Table 1 for each
size.

2. Remove the current speed tap wire from the “LOW”

terminal on the interface fan board (IFB) (See Fig. 13) and
place vinyl cap over the connector on the wire.

3. Connect the desired speed tap wire to the “LOW” terminal

on the interface fan board (IFB).

Two Cooling Fan Speeds Set-up (Dehumidification

feature used)

IMPORTANT

: Dehumidification control must open control

circuit on humidity rise above set point.
Use of the dehumidification cooling fan speed requires use of
either a 24 VAC dehumidistat or a thermostat which includes

control of a 24 VAC dehumidistat connection. In either case, the
dehumidification control must open the control circuit on humidity

rise above the dehumidification set point. Dehumidification

controls are available with the reverse logic; these must not be
used.

1. Remove fan speed tap wire from the “LOW” terminal on

the interface fan board (IFB) (See Fig. 13).

2. Determine correct normal cooling fan speed for unit and

application. Add the wet coil pressure drop in Table 8 to
the system static to determine the correct cooling airflow

speed in Table 10 that will deliver the nominal cooling
airflow as listed in Table 1 for each size.

3. Remove the vinyl cap off of the desired speed tap wire

(Refer to Table 6 for color coding) for the normal cooling
fan speed and place desired speed tap wire on “HIGH” on

the interface board.

4. Refer to airflow tables (Table 10) to determine allowable

speeds for the dehumidification cooling fan speed. In Table
10, speeds that are not allowed for dehumidification cooling
are shaded.

5. Remove the vinyl cap off of the desired speed tap wire

(Refer to Table 6 for color coding) for the dehumidification

cooling fan speed and place desired speed tap wire on the
“LOW” connection on the interface board (IFB). Verify
that static pressure is in the acceptable range for the speed

tap to be used for dehumidification cooling.

6. Use any spare vinyl plugs to cap any unused speed tap

wires.

Continuous Fan Operation

When the DEHUM feature is not used, the continuous fan speed

will be the same as cooling fan speed. When the DEHUM feature
is used, the continuous fan will operate on IFB “LOW” speed

when the DH control lead is not energized, or IFB “HIGH” speed

when the DH lead is energized (see Fig. 13).

NOTE

: For heat pump operation, the recommended airflow is 350

to 450 CFM for each 12,000 Btuh of rated cooling capacity.

Table 6 – Color Coding for Indoor Fan Motor Leads