Checking Temperature Rise; Checking Primary Limit Control - Goodman GMEC96 Service Instructions Manual

SERVICING
To determine proper air movement, proceed as follows:
1. With clean filters in the furnace, use a draft gauge (in-
clined manometer) to measure the static pressure of
the return duct at the inlet of the furnace. (Negative Pres-
sure)
2. Measure the static pressure of the supply duct. (Posi-
tive 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 condi-
tioner coil or Electronic Air Cleaner is used in conjunction
with the furnace, the readings must also include theses com-
ponents, 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, reg-
isters, 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 deliv-
ered, 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.
Checking Temperature Rise
3. Subtract the return air temperature from the supply air
temperature to determine the air temperature rise. Allow
adequate time for thermometer readings to stabilize.
4. Adjust temperature rise by adjusting the circulator blower
speed. Increase blower speed to reduce temperature rise.
Decrease blower speed to increase temperature rise.
Refer to Circulator Blower Speed section in the Product
Design section of this manual for speed changing de-
tails. Temperature rise is related to the BTUH output of
the furnace and the amount of air (CFM) circulated over
the heat exchanger. Measure motor current draw to de-
termine that the motor is not overloaded during adjust-
ments.
S-300 CHECKING PRIMARY LIMIT CONTROL
All primary limit controls are nonadjustable, automatic re-
set, bi-metal type limit control. Refer to the following draw-
ing for the location of the primary limit.
SUPPLY
AIR
RETURN
AIR
57