After which the BLWM operates at the appropriate oil
heating airflow. The BLWM reverts to continuous blower
airflow after the heating cycle is completed.
c. When thermostat
″
calls for low-cooling
″
, the BLWM keeps
continuous-blower speed until the end of
″
Short run
″
delay
period. After which the BLWM operates at the appropriate
low cooling airflow. When the thermostat is satisfied, the
BLWM switches to continuous-blower airflow.
d. When the thermostat calls for high cooling, the BLWM
keep continuous-blower speed until the end of
″
Short run
″
delay period. After which the BLWM operates at the
appropriate high cooling airflow.
e. When R-G circuit is opened, the BLWM stops immedi-
ately.
HEAT PUMP
NOTE:
A dual-fuel thermostat is required when variable speed
furnaces are used with heat pumps. See dual-fuel thermostat
Installation Instructions for interface connections. The interface
prevents simultaneous operation of both furnace and heat pump,
and prevents direct transition from heat pump to furnace operation.
a. Single-Speed Heat Pump Cooling
(1.) The thermostats close the R to Y/Y2-and-G-and-O
circuits to operate the Furnace BLWM at cooling
airflow. The Y/Y2 input to the furnace control is
necessary to provide adequate cooling airflow.
(2.) When thermostat is satisfied, furnace BLWM contin-
ues operating at 50 percent of the cooling airflow for
an additional 3 min
b. Two-Speed Heat Pump Cooling
(1.) The thermostat closes the R to G-and-Y1-and-O
circuits to operate the furnace BLWM at low-cool
airflow. The thermostat R to G-and-Y/Y2-and-Y1-
and-O circuits operates the furnace BLWM at high-
cool airflow.
NOTE:
The furnace control CPU controls blower airflow by
sensing G, Y1, and O for low-cool airflow and G, Y1, Y/Y2, and
O for 2-speed high-cool airflow.
(2.) When the thermostat is satisfied, the furnace BLWM
continues operating at 50 percent of the additional 3
min.
c. Single-Speed Heat Pump Heating
(1.) The thermostats close R to G-and-Y/Y2 circuits to
operate the furnace BLWM at heat pump heating
airflow. Heating airflow is the same as cooling air-
flow.
(2.) When thermostat is satisfied, the furnace BLWM
continues operating at 50 percent of the heat pump
heating airflow for an additional 3 min.
d. Two-Speed Heat Pump Heating
(1.) The thermostat closes the R to Y1-and-G circuits for
low heat and operates the furnace BLWM at heat
pump low-heat airflow. Closing R-Y/Y2, Y1 and G
circuit to furnace provides BLWM heat pump high-
heat airflow.
NOTE:
The furnace control CPU controls BLWM airflow by
sensing G and Y1 for heat pump low-heat airflow, and G, Y1, and
Y/Y2 for heat pump high-heat airflow.
(2.) When the thermostat is satisfied, the furnace BLWM
continues operating at 50 percent heating airflow for
an additional 3 min.
(3.) Opening only R-Y/Y2 circuit switches BLWM to heat
pump low-heat airflow.
DEFROST
When furnace controls R to W/W1-and-Y/Y2 circuits are closed,
furnace control CPU starts and burner and BLWM operation is at
oil heating airflow during defrost.
Step 3—Combustion Check
In order to obtain optimum performance from oil burner, the
following setup procedures must be followed:
1. A test kit to measure smoke, stack draft, over-fire draft, CO
2
,
oil pump pressure, and stack temperatures MUST be used in
order to obtain proper air band setting. Although all of the
above measurements are required for optimum setup and
efficiency data, the most important readings that must be taken
are smoke number, over-fire draft, stack draft, and pump
pressure.
2. The proper smoke number has been established by engineer-
ing tests to be between 0 and 1. This degree of smoke emission
is commonly referred to as a
″
trace
″
of smoke. It is recom-
mended to use a Bacharach true spot smoke test set or
equivalent.
3. In order to ensure proper draft through furnace, a barometric
draft regulator (supplied with furnace) must be installed.
In order for this device to function properly, barometric
damper must be mounted with hinge pins horizontal and face
of damper vertical. (See instructions included with damper.)
The draft regulator should be adjusted after furnace has been
firing for at least 5 minutes, and set between -0.025 and -0.035
in. wc. (See Table 9.)
4. The over-fire draft, which is taken through observation door
(located in center line above burner in front panel of furnace),
is a measurement necessary to determine if there is a blockage
between oil burner and flue outlet.
There should be a total pressure drop of between 0.020 and
0.05 in. wc through furnace as shown in Table 9. The over-fire
draft must be set within the range shown in Table 9. A reading
outside the range shown in Table 9 (for e0.1 in. wc)
would indicate that furnace is in an extremely high-pressure
condition in primary section. This condition may be caused by
any of the following problems:
a. Excessive combustion air due to air shutter being too wide
open.
b. A lack of flue draft (chimney effect) or some other
blockage, such as soot, in secondary section of heat
exchanger.
c. Use of an oversized nozzle input.
d. Pump pressure over the values listed in Table 10.
Table 9—Furnace Draft Conditions
(In. wc)
FURNACE
INPUT
(BTUH)
FLUE
DRAFT
MINIMUM
OVER-FIRE
DRAFT
MAXIMUM
TOTAL RESTRICTION
THROUGH
HEAT EXCHANGER
70,000
–0.025
0.010
0.020 to 0.035
91,000
–0.025
0.020
0.030 to 0.045
105,000
–0.025
0.025
0.035 to 0.050
119,000
–0.025
0.025
0.035 to 0.050
140,000
–0.025
0.025
0.035 to 0.050
154,000
–0.025
0.025
0.035 to 0.050
11