SERVICING
32
CONNECTOR ID
DESCRIPTION
CONNECTOR VOLTAGE
L
LINE, L1
LINE, L1
G
GROUND
CHASSIS GROUND
N
LINE, L2
LINE, L2
C
SIGNAL COMMON 24VAC COMMON
1
TAP 1
24VAC
2
TAP 2
24VAC
3
TAP 3
24VAC
4
TAP 4
24VAC
5
TAP 5
24VAC
Motor Tap Identification
WARNING
Disconnect ALL power before servicing.
CHECKING DUCT STATIC
The maximum and minimum allowable external static pres
-
sures 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 insuffi
-
cient air that can cause excessive temperature rise, result
-
ing in limit tripping, etc. Whereas not enough static may re-
sult in motor overloading.
To determine proper air movement, 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.
(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
(80% Furnace Shown, 90% Similar)
CHECKING TEMPERATURE RISE
The more air (CFM) being delivered through a given fur-
nace, 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 ex
-
ceed 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
