Daikin DM80SE, Service Instructions Manual

Page: 26 / 34

26
SERVICING
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.
SUPPLY
AIR
RETURN
AIR
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
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.
CHECKING PRIMARY LIMIT CONTROL
All use a nonadjustable, automatic reset, bi-metal type limit
control.
Style 1 drawing illustrates the Primary Limit used on the
80% furnaces.
Style 1
WARNING
HIGH VOLTAGE
D
ISCONNECT
ALL
POWER BEFORE SERVICING OR
CHANGING ANY ELECTRICAL WIRING.
M
ULTIPLE POWER
SOURCES MAY BE PRESENT.
F
AILURE TO DO SO MAY CAUSE
PROPERTY DAMAGE, PERSONAL INJURY OR DEATH.
1. Remove burner compartment door to gain access to
the primary limit.
2. Remove low voltage wires at limit control terminals.
3. With an ohmmeter, test between these two terminals
as shown in the following drawing. The ohmmeter
should read continuous unless heat exchanger tem -
perature is above limit control setting. If not as above,
replace the control.
Testing Primary Limit Control