Superheat And Subcooling - Daikin DFG Series Installation Instructions Manual

9. Integrated ignition control will close its normally open
contacts after a delay of approximately 30 seconds. This
action energizes contactor BC and starts the supply fan
motor. Operation of the supply fan circulates air across
the heat exchanger and delivers heated air to the condi-
tioned space.
10. When the space temperature rises, the thermostat will
open R-W. Opening R-W will cause the gas valve to close,
and the furnace to shut down.
11. The furnace has three high temperature limit controls,
which can shut down the burner. They do not shut down
the vent motor.
Unit Shutdown
1. Set the thermostat to lowest setting.
2. Turn off the electrical power supply to the unit.
3. Remove the heat exchanger door on the side of the unit
by removing screws.
4. Move the gas control valve switch to the OFF position. Do
not force.
5. Close manual gas shut off valve external to the unit.
6. Replace the heat exchanger door on the unit.
7. If cooling and/or air circulation will be desired, turn ON
the electrical power.
Automatic Reset High Limit Control (LS)
Located in the burner compartment on the heat exchanger, its
sensing element projects through the blower section bulkhead
and senses the temperature at the rear of the furnace. It will cycle
the furnace off if the temperature exceeds 100°F plus maximum
rise.
Auxiliary Reset High Limit Control (ALS)
Located in the blower compartment on the blower housing, it
senses air temperature within the blower compartment and pro-
tects the filters from excessive temperature. It will shut down the
furnace if it senses excessive temperatures.
Elevated temperatures at the control are normally caused by
blower failure. The reason for the opening should be determined
and repaired prior to resetting.
Manual Reset Flame Rollout Control (RS)
Located in the burner compartment at the top of the burner as-
sembly, it senses high temperature that could occur if the heat
exchanger tubes were plugged and the flame was rolling out in-
stead of entering the tubes. It has a manual push-button reset
that cannot be actuated until the limit control has cooled.
The reason for elevated temperatures at the control should be
determined and repaired prior to resetting this manual reset
control.
To avoid property damage, personal injury or death due to
fire or explosion, a qualified servicer must investigate the
reason for the rollout protection device to open before
manually resetting the rollout protection device.
Refrigeration System
The unit is equipped with a thermal expansion valve as a metering
device.
Ensure the hold-down bolts on the compressor are secure and
have not vibrated loose during shipment. Check that vibration
grommets have been installed. Visually check all piping for dam-
age and leaks; repair if necessary. The entire system has been fac-
tory charged and tested, making it unnecessary to field charge.
Factory charges are shown on the unit's nameplate. To confirm
charge levels or, if a leak occurs and charge needs to be added
to the system, it is recommended to evacuate the system and re-
charge refrigerant to unit nameplate specifications.
This unit has been rated in the cooling mode at the AHRI rated
conditions of: Indoor (80°db / 67°wb) and outdoor (95°db).
While operating at this condition, the superheat and subcool for
each circuit for each unit should fall within the values listed in
the table below. The superheat is measured at the suction service
port located near the compressor. The subcool is measured at the
liquid line service port.

SUPERHEAT AND SUBCOOLING

Checking Subcooling
NOTE: Units with a TXV should be charged to Subcooling only.
Make sure the air flow is correct before making any adjustments.
EXAMPLE:
a. Liquid Line Pressure = 417 PSI
b. Corresponding Temp. = 120°F
c. Thermometer on Liquid line = 109°F.
To obtain the amount of subcooling, subtract 109°F from 120°F.
The difference is 11° subcooling. See the specification sheet or
technical information manual for the design subcooling range for
your unit.
SUBCOOLING FORMULA = SATURATED LIQUID LINE TEMPERA-
TURE - LIQUID LINE TEMPERATURE
Checking Superheat
EXAMPLE:
a. Suction Pressure = 143 PSI
b. Corresponding Temp. = 50°F
c. Thermometer on Suction Line = 59°F
To obtain the degrees temperature of superheat, subtract 50.0
from 59.0°F. The difference is 9° Superheat. The 9° Superheat
would fall in the ± range of allowable superheat.
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WARNING