Williamson-Thermoflo PLB-098 LOW-BOY, Instructions Manual, Page: 10 / 26

PLB-098
Oil Furnaces
– Furnace Manual
10 11/13
1.9.2. Ducting
Poisonous carbon monoxide gas hazard.
DO NOT draw return air from inside a closet or
utility room. Return air MUST be sealed to the
furnace casing.
Failure to properly seal ducts can result in death,
bodily injury and/or property damage.
The ducting must be designed and installed according to approved
methods, local and national codes as well as good trade practices.
When ducting supplies air to a space other than where the furnace is
located, the return air must be sealed and also be directed to the
space other than where the furnace is located.
1.9.3. Air filter
A properly sized air filter must be installed on the return air side of
the unit. Refer to table 10, for the correct dimensions. Also refer to
the instructions supplied with the filter.
1.10. SUPPLY AIR ADJUSTMENTS
(4-SPEED MOTORS)
On units equipped with 4-speed blower motors, the supply air must
be adjusted based on heating/air conditioning output and the static
pressure of the duct system. For the desired air flow refer to the
following table as well as the air flow tables based on static pressure
in the table 12 of this manual.
Table 5: Blower speed adjustments
(4-speed motors)
FURNACE HEATING OR A/C RECOMMENDED
APPLICATION OUTPUT BLOWER SPEED
0.50 USGPH MED-LOW
0.60 USGPH MED-HIGH
0.70 USGPH HIGH
2.0 TONS MED-LOW
2.5 TONS MED-HIGH
3.0 TONS HIGH
HEATING
A/C
To effect the adjustment, the RED (for heating) and BLUE (for
cooling and heat pump) wires can be changed on the motor. Also,
refer to the position of the wires on the electronic board of the unit
and consult the wiring diagrams. If the heating and air conditioning
speeds are the same, the RED wire must be moved to “UNUSED
LEADS” on the electronic board and the jumper provided with the
BLUE wire must be used between the “HEAT” and “COOL”
terminals.
The blower start/stop delays can be adjusted by positioning the DIP
switches on the electronic board as shown in the following figures.
The recommended blower ON delay is 60 seconds and the blower
OFF delay is 2 minutes.
Figure 8: Blower start/stop delays
Board # 1158
1.11. SUPPLY AIR ADJUSTMENTS
(ECM VARIABLE-SPEED MOTORS)
On units equipped with ECM variable speed blower motors, the air
supply must be adjusted based on heating/air conditioning output.
The start/stop delays of the blower must also be adjusted by
positioning the DIP switches on the electronic board. Refer to the
following tables, air flow table 13 and the wiring diagram, figure 10 in
this manual for the proper settings:
Table 6: Supply air adjustments, ECM variable speed
motors, heating mode
1 2 POSITION
OFF OFF A 0.70
ON OFF B 0.60
OFF ON C 0.50
ON ON D ALL
SW1 – HEAT
Input
USGPH
DIP Switch Positions
Table 7: Supply air adjustments, ECM variable speed
motors, air conditioning mode
1 2 POSITION
OFF OFF A 3.0
ON OFF B 2.5
OFF ON C 2.0
ON ON D 1.5
SW2 – COOL
Output Tons
DIP Switch Positions
Table 8: CFM adjustments, all modes
CFM HTG. CFM A/C
% increase % increase
1 2 POSITION
or decrease or decrease
OFF OFF A 0% 0%
ON OFF B 10% 10%
OFF ON C -10% -10%
ON ON D N/A 0%
SW3 – ADJ (Adjustment)
DIP Switch Positions
Table 9: Delay adjustments - heating mode
1 2 POSITION
OFF OFF A 0.70
ON OFF B 0.60
OFF ON C 0.50
ON ON D ALL
SW4 – Delay
Input
USGPH
DIP Switch Positions