45
IOM
W415-2288 / 08.29.2019
No adjustments are required or should be attempted regarding any of the components of the cooling section.
The cooling section should be checked to see that none of the wiring is loose or missing. Cooling section is
charged with R410A refrigerant.
6.3.3 Adjustments – Cooling
6.3.2 Calculating air ow / Capacity Check
H22.2.1
There are circumstances where it may be desirable to know the air ow delivery through the duct system,
such as when estimating the amount of air ow available for
air conditioning. This can be done by direct measurement with
electronic or sloped manometers and velometers, or use the
formula in the next column.
CFM =
Output
1.085 x
∆T
where:
• CFM is air ow in cubic feet per minute;
• ∆T is the temperature rise; and
• Output is the furnace output capacity
from the rating plate
.
5. Compare the measured ∆T to the temperature rise range shown on the rating plate.
6. Unless stated differently on the rating plate, the temperature rise should normally range between 35°
to 65°F (20° to 36°C). When adjusting the temperature rise, the ideal temperature rise is approximately
50°F (28°C).
7. If the measured ∆T is above the approved temperature range, there is too little air ow. It must be
increased by removing restrictions in the ductwork, adding supply or return ductwork, or by selecting a
higher motor speed.
*** If the measured ∆T is too low, there is too much air ow.
When the duct system is complete and the air lter or lters are in place, determine if the airow is correct.
1. Insert a duct thermometer in the supply air duct. The thermometer should be placed as close as practical
to the heat module, but out of the “line of sight” of the heat element (this prevents false readings owing to
radiant heat). Ensure that the thermometer location is within the duct air stream. Avoid locations such as
the inside radius of an elbow, etc.
2. Insert a duct thermometer in the return air duct as close to the unit inlet opening as practical. Ensure that
the thermometer location will be unaffected by humidier bypass ducts, etc. Choose a location well within
the main air stream.
3. Operate the heating module long enough to obtain steady state conditions at the input listed on the unit
rating plate.
4. When the two thermometers have stabilized, usually within 5-8 minutes, compare the two readings.
Subtract the return air temperature from the supply air temperature. The difference is the temperature rise,
also called ∆T.
6.3.1 Temperature Rise Check (In Heating mode)
6.3 AIR FLOW
H22.0.2
For proper heating operation, air ow over the heating elements is of utmost importance. Insuf cient air ow
accelerates metal fatigue and possible failure in the heat elements, as well as increases the possibility of the
furnace being shut down by the high temparature limit switches.
DO NOT BYPASS THIS STEP OF THE START UP PROCEDURES.
IMPORTANT
!
!
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