Friedrich VERT-I-PAK VHA-18K75RTP, Service & Parts Manual

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38 PB
Fresh Air Door
The Fresh Air Door is an “intake” system. The fresh air door opened via a slide on the front of the chassis located just above the indoor coil. Move the slide left
to open and right to close the fresh air door. The system is capable of up to 60 CFM of fresh air @ ~.3” H20 internal static pressure.
Checking Approximate Airflow
If an inclined manometer or Magnehelic gauge is not available to check the External Static Pressure, or the blower performance data is unavailable for your
unit, approximate air fl ow call be calculated by measuring the temperature rise, then using tile following criteria.
CFM =
Kilowatts × 3413
Temp Rise × 1.08
Electric Heat Strips
The approximate CFM actually being delivered can be calculated by using the following formula:
DO NOT
simply use the Kilowatt Rating of the heater (i.e. 2.5, 3.4, 5.0) as this will result in a less-than-correct airfl ow cal -
culation. Kilowatts may be calculated by multiplying the measured voltage to the unit (heater) times the measured current
draw of all heaters (ONLY) in operation to obtain watts. Kilowatts are than obtained by dividing by 1000.
EXAMPLE: Measured voltage to unit (heaters) is 230 volts. Measured Current Draw of strip heaters is 11.0 amps.
230 x 11.0 = 2530
2530/1000 = 2.53 Kilowatts
2.53 x 3413 = 8635
Supply Air = 95°F
Return Air = - 75°F
Temperature Rise = 20°F
20 x 1.08 = 21.6
8635
21.6 = 400
External Static Pressure