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Limit Check
Check limit control operation after 15 minutes of operation
by blocking the return air grille(s).
1. After several minutes the main burners must go OFF.
Blower will continue to run.
2. Remove air restrictions and main burners will relight
after a cool down period of a few minutes.
Adjust the thermostat setting below room temperature.
1. Main burners must go OFF.
2. Circulating Air Blower will continue to run for 90, 120,
150 or 180 seconds, depending on the setting.
NOTE: If necessary, adjust fan OFF delay settings to obtain
satisfactory comfort level.
PCBAG127 Ignition Module
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 shutoff 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.
Cooling Start-up
NOTE: Check all manual reset limit controls in heating
circuit if cooling mode does not operate.
Compressor Protection Devices
The compressor includes components which are de-
signed to protect the compressor against abnormal op-
erating conditions.
Checking Subcooling
NOTE: Units with a TXV should be charged to Subcool-
ing only.
SUBCOOLING FORMULA = SATURATED LIQUID LINE
TEMPERATURE - LIQUID LINE TEMPERATURE
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 subcool-
ing range for your unit.
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° Su-
perheat would fall in the ± range of allowable superheat.
SUPERHEAT = SUCTION LINE TEMP - SAT. SUCTION
TEMP.
Superheat Adjustment
NOTE: Superheat adjustments should not be made until in-
door ambient conditions have stabilized. This could take up
to 24 hours depending on indoor temperature and humidity.
Before checking superheat run the unit in cooling for 10-15
minutes or until refrigerant pressues stabilize. Use the fol-
lowing guidelines and methods to check unit operation and
ensure that the refrigerant charge is within limits.
For TXV systems, to adjust superheat, unscrew the cover
from the expansion valve, locate the adjustment screw, and
turn it clockwise (in) to increase superheat or counterclock-
wise (out) to decrease superheat. It is recommended to
make small adjustments at a time, 1/8-1/4 turn increments.
Replace adjustment cap. Wait a minimum of 10 minutes
between adjustments to allow time for the TXV and pres-
sures to stabilize.
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