13
Electric resistance heaters can use
CFM =
volts x amps x 3.414
1.08 x temp rise
Gas furnaces can use
CFM =
BTUH
ΔT x 1.08
An air velocity meter or airflow hood can give a more accurate reading of the sys-
tem CFM.
CHECKING REFRIGERANT CHARGE
Charge for all systems should be checked against the Charging Chart inside the
access panel cover.
CHARGING BY LIQUID PRESSURE
The liquid pressure method is used for charging systems in the cooling mode. The
service port on the liquid (small valve) and suction (large valve) is used for this pur-
pose.
Verify that the outdoor unit is running and the indoor air mover is delivering the cor-
rect airflow for this system size. Read and record the liquid pressures at the ports
on the liquid and suction valves.
If refrigerant lines are 15 feet long, the correct liquid pressure is found at the inter-
section of the suction pressure and the outdoor ambient.
1. Remove refrigerant charge if the liquid pressure is above the chart value.
2. Add refrigerant charge if the liquid pressure is below the chart value.
If the refrigerant lines utilized extend 15 feet, add 4 psi to the liquid pressure values
shown in the chart.
1. Remove refrigerant charge if the liquid pressure is above the chart value.
2. Add refrigerant charge if the liquid pressure is below the chart value.
CHARGING BY WEIGHT
For a new installation, evacuation of interconnecting tubing and evaporator coil is
adequate; otherwise, evacuate the entire system. Use the factory charge shown in
Table 1 of these instructions or unit data plate. Note that charge value includes
charge required for 15 ft. of standard size interconnecting liquid line. Calculate actu-
al charge required with installed liquid line size and length using:
1/4” O.D. = .3 oz./ft.
5/16” O.D. = .4 oz./ft.
3/8” O.D. = .6 oz./ft.
1/2” O.D. = 1.2 oz./ft.
With an accurate scale (+/– 1 oz.) or volumetric charging device, adjust charge dif-
ference between that shown on the unit data plate and that calculated for the new
system installation. If the entire system has been evacuated, add the total calculat-
ed charge.
FINAL LEAK TESTING
After the unit has been properly evacuated and charged, a halogen leak detector
should be used to detect leaks in the system. All piping within the condensing unit,
evaporator, and interconnecting tubing should be checked for leaks. If a leak is
detected, the refrigerant should be recovered before repairing the leak. The Clean
Air Act prohibits venting refrigerant into the atmosphere.
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