York DM120 Installation Manual download pdf (Page 56)

264973-YIM-A-0806

56 Unitary Products Group

AIR BALANCE

Start the supply air blower motor. Adjust the resistances in both the supply and the return air duct systems to balance the air dis-

tribution throughout the conditioned space. The job specifications may require that this balancing be done by someone other

than the equipment installer.

CHECKING AIR QUANTITY

METHOD ONE

1. Remove the dot plugs from the duct panel (for location of

the dot plugs see Figure 10).

2. Insert eight-inches of 1/4 inch metal tubing into the air-

flow on both sides of the indoor coil.

NOTE: The tubes must be inserted and held in a position

perpendicular to the air flow so that velocity pres-

sure will not affect the static pressure readings.

3. Use an Inclined Manometer or Magnehelic to determine

the pressure drop across a dry evaporator coil. Since the

moisture on an evaporator coil can vary greatly, measur-

ing the pressure drop across a wet coil under field condi-

tions could be inaccurate. To assure a dry coil, the

compressors should be de-activated while the test is

being run.

NOTE: De-energize the compressors before taking any test

measurements to assure a dry evaporator coil.

4. The CFM through the unit can be determined from the

pressure drop indicated by the manometer by referring to

Figure 26. In order to obtain an accurate measurement,

be certain that the air filters are clean.

5. To adjust Measured CFM to Required CFM, see ’SUP-

PLY AIR DRIVE ADJUSTMENT’.

6. After readings have been obtained, remove the tubes

and replace the dot plugs.

METHOD TWO

1. Drill two 5/16 inch holes, one in the return air duct as

close to the inlet of the unit as possible, and another in

the supply air duct as close to the outlet of the unit as

possible.

2. Using the whole drilled in step 1, insert eight inches of

1/4 inch metal tubing into the airflow of the return and

supply air ducts of the unit.

NOTE: The tubes must be inserted and held in position per-

pendicular to the airflow so that velocity pressure

will not affect the static pressure readings.

3. Use an Inclined Manometer or Magnehelic to determine

the pressure drop across the unit. This is the External

Static Pressure (ESP). In order to obtain an accurate

measurement, be certain that the air filters are clean.

4. Determine the number of turns the variable motor

sheave is open.

5. Select the correct blower performance table for the unit

from Tables 35 - 46. Tables are presented for horizontal

and downflow configuration.

6. Determine the unit Measured CFM from the Blower Per-

formance Table, External Static Pressure and the num-

ber of turns the variable motor sheave is open.

7. To adjust Measured CFM to Required CFM, see ’SUP-

PLY AIR DRIVE ADJUSTMENT’.

8. After reading has been obtained, remove the tubes and

seal holes.

NOTE: With the addition of field installed accessories

repeat this procedure.

Failure to properly adjust the total system air quan-

tity can result in extensive blower damage.

Failure to properly adjust the total system air quan-

tity can result in extensive blower damage.

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York DM120 Installation Manual Page 56

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