45
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.
CUTAWAY OF DUCTWORK
TO EXPOSE COIL
INCLINED
MANOMETER
RETURN
AIR
SUPPLY
AIR
Checking Static Pressure
COOL MOTOR SPEED DIP SWITCH SETTING (S1-1, S1-2, S1-3)
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
*
= DEFAULT SETTING
HEAT MOTOR SPEED DIP SWITCH SETTING (S2-1, S2-2)
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
*
= DEFAULT SETTING
FAN MOTOR SPEED DIP SWITCH SETTING (S2-3, S2-4)
*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
*
= DEFAULT SETTING
D
ISCONNECT
ALL
POWER BEFORE SERVICING.
WARNING
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.
