Checking Temperature Rise; Checking Primary Limit Control - Maytag Goodman GM9C96 Service And Troubleshooting

SERVICING

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.
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

CHECKING PRIMARY LIMIT CONTROL

All primary limit controls are nonadjustable, automatic reset,
bi-metal type limit control. Refer to the following drawing for
the location of the primary limit.
SUPPLY
The following drawing illustrates the style of limit switches
AIR
used on the 90% furnaces.
RETURN
AIR
HIGH VOLTAGE
D
ISCONNECT
CHANGING ANY ELECTRICAL WIRING.
SOURCES MAY BE PRESENT.
PROPERTY DAMAGE, PERSONAL INJURY OR DEATH.
1. Remove burner compartment door to gain access to
2. Remove low voltage wires at limit control terminals.
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 details.
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 determine
that the motor is not overloaded during adjustments.
Primary Limit Control Location
(90% Upflow Furnace Shown)
FRONT VIEW
Primary Limit Control Style
(90% Furnaces)
WARNING
ALL
POWER BEFORE SERVICING OR
F
AILURE TO DO SO MAY CAUSE
the primary limit.
ENCLOSED DISK
SIDE VIEW
M
ULTIPLE POWER
25