Bryant Model 378 - Manual (Page 5)

3. Thermostat connections for heating only are to
be made at terminals 4 and W. See Figure 3 for low
voltage connections when cooling equipment is
used.
4. A separate, fused, electrical line should be run
for this installation.
START-UP AND ADJUSTMENT
1. Before Starting the Unit:
a. Check to see that electric and piping con­
nections have been made.
b. Make sure gas piping is purged and free of
air; do not purge into the combustion chamber
of the furnace. All gas piping connections
should be leak tested. Do not use an open
flame. Use a soap and water solution.
2. Start-Up:
'Follow lighting instructions attached to the unit.
Sequence of control operation is as follows:
a. When pilot gas cock is opened, gas flows to
the pilot and to the pilot pressure switch.
b. Pilot pressure switch then closes to com­
plete the 24 volt circuit. The pilot then
lights automatically.
c. Subsequent switch action completes circuit
through Y and W to energize the electric gas
valve.
When the thermostat calls for heat, circuit is closed
between W and 4. This allows current to flow through
combustion air fan relay which energizes the com­
bustion air blower and builds up pressure in the
combustion air switch. When combustion air pres­
sure switch is closed, low voltage is completed.
The conditioning air blower is not actuated by a fan
switch, but by a delay fan relay.
If the lower limit opens, the automatic gas valve is
de-energized.
If the upper limit opens, the automatic gas valve is
de-energized, and the combustion air pressure switch
is by-passed so that the conditioning air blower will
continue to run.
unit. The limit will shut off the main gas if the
temperature goes too high. The limit may be checked
by removing the fan belt and firing the unit. The
burners should shut in a few minutes.
3. Adjust Gas Input:
Air Shutter Adjustment - To adjust the air shutter,
pull the shutter closed until there is a slight yellow
tip at the top of each flame. Then open the shutter
until the yellow tip disappears.
Gas input should agree with that shown on the rating
plate of the unit. The burners are equipped with
orifices sized to give the correct input with a mani­
fold pressure of 3 inches w.c. ± 0.3 for natural and
mixed gases, and II inches w.c. for propane gas.
The furnaces are approved for minimum firing rates
(shown on rating plate) as follows:
Size 150 - May be fired at 100,000 BTUH input.
Size 300 - May be fired at 200,000 BTUH input
Note: The size 150 furnace (natural gas only) is
also approved for modulated input down to 50,000
BTUH when equipped with an approved modulating
valve. The size 300 furnace (natural gas only) is
approved for modulated input down to 100,000 BTUH.
See next page for
Gas Input Measurement
The automatic pilot turns the main gas off, should
pilot flame be put out. This can be checked by turn­
ing the main burners and pilot oh, then shutting the
pilot gas off. The main burners should shut off.
The limit controls the temperature reached in the
5 - EH 378