SERVICING
37
1 2 3
1 2 3
1 2 3
1 2 3
Position OFF OFF OFF ON OFF OFF ON ON OFF OFF ON OFF
Motor
Speed
COOL
Y
T1
T2
T3
T4
*1 2 3
1 2 3
1 2 3
1 2 3
Position OFF OFF ON OFF ON ON ON OFF ON ON ON ON
Motor
Speed
COOL
Y
T1+T2
T1
T1
T1
COOL MOTOR SPEED DIP SWITCH SETTING (S1-1, S1-2, S1-3)
*
= DEFAULT SETTING
1 2
*1 2
1 2
1 2
Position OFF OFF ON OFF ON ON OFF ON
Motor
Speed
HEAT
W
T1
T2
T3
T4
HEAT MOTOR SPEED DIP SWITCH SETTING (S2-1, S2-2)
*
= DEFAULT SETTING
*3 4
3 4
3 4
3 4
Position OFF OFF ON OFF OFF ON ON ON
Motor
Speed
FAN
G
T1
T2
T4 T1+T2
FAN MOTOR SPEED DIP SWITCH SETTING (S2-3, S2-4)
*
= DEFAULT SETTING
S-200 CHECKING DUCT STATIC
The maximum and minimum allowable external static
pressures are found in the specification section. These tables
also show the amount of air being delivered at a given static
by a given motor speed or pulley adjustment.
The furnace motor cannot deliver proper air quantities (CFM)
against statics other than those listed.
Too great of an external static pressure will result in insufficient
air that can cause excessive temperature rise, resulting in
limit tripping, etc. Whereas not enough static may result in
motor overloading.
To determine proper air movement, proceed as follows:
1. With clean filters in the furnace, use a draft gauge (inclined
manometer) to measure the static pressure of the return
duct at the inlet of the furnace. (Negative Pressure)
2. Measure the static pressure of the supply duct. (Positive
Pressure)
3. Add the two (2) readings together for total external static
pressure.
NOTE:
Both readings may be taken simultaneously and read
directly on the manometer if so desired. If an air conditioner
coil or Electronic Air Cleaner is used in conjunction with the
furnace, the readings must also include theses components,
as shown in the following drawing.
4. Consult proper tables for the quantity of air.
If the total external static pressure exceeds the minimum
or maximum allowable statics, check for closed dampers,
registers, undersized and/or oversized poorly laid out duct
work.
Checking Static Pressure
S-201 CHECKING TEMPERATURE RISE
The more air (CFM) being delivered through a given furnace,
the less the rise will be; so the less air (CFM) being
delivered, the greater the rise. The temperature rise should
be adjusted in accordance to a given furnace specifications
and its external static pressure. An incorrect temperature
rise may result in condensing in or overheating of the heat
exchanger. An airflow and temperature rise table is provided
in the blower performance specification section. Determine
and adjust temperature rise as follows:
1. Operate furnace with burners firing for approximately ten
minutes. Check BTU input to furnace - do not exceed
input rating stamped on rating plate. Ensure all registers
are open and all duct dampers are in their final (fully or
partially open) position.
2. Place thermometers in the return and supply ducts as
close to the furnace as possible. Thermometers must not
be influenced by radiant heat by being able to “see” the
heat exchanger.
SUPPLY
AIR
RETURN
AIR
Checking Temperature Rise
