23
by removing the “A” shaped block off plate from the end on
the coil; drilling a test hole in it and reinstalling the block off
plate. Take a duct static reading at the test hole. Tape up the
test hole after your test is complete. The negative pressure
must be read between the filter and the furnace blower.
Excessive external static pressure will result in insufficient air
that can cause excessive temperature rise. This can cause
limit switch tripping and heat exchanger failure.
To determine total external duct static pressure, proceed as
follows:
1.
With clean filters in the furnace, use a 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. (Posi-
tive Pressure)
3.
The difference between the two numbers is .4” w.c.
Example:
static reading from return duct = -.1” w.c.
static reading from supply duct = .3” w.c.
total external static pressure on this system = .4” w.c.
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 maximum
listed on the furnace rating plate, check for closed dampers,
registers, undersized and/or oversized poorly laid out duct
work.
Digital
Manometer
Checking Static Pressure
1 2 3
1 2 3
Position
OFF OFF OFF
ON OFF OFF
Motor Speed
COOL
Y
T1
T2
1 2 3
1 2 3
*1 2 3
ON ON OFF
OFF ON OFF
OFF OFF ON
Motor Speed
COOL
T3
T4
T1+T2
1 2 3
1 2 3
1 2 3
OFF ON ON
ON OFF ON
ON ON ON
Motor Speed
COOL
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
OPERATIONAL CHECKS
WARNING
To avoid personal injury or death, do not remove any internal
compartment covers or attempt any adjustment. Electrical
components are contained in both compartments. Contact
a qualified service agent at once if an abnormal flame
appearance should develop.
Checking Duct Static
Refer to your furnace rating plate for the maximum ESP (ex-
ternal duct static) rating.
Total external static refers to everything external to the fur-
nace cabinet. Cooling coils, filters, ducts, grilles, registers
must all be considered when reading your total external stat-
ic pressure. The supply duct pressure must be read between
the furnace and the cooling coil. This reading is usually taken
