York PREDATOR DM090 Installation Manual

Also see for PREDATOR DM 090: Installation manual Technical guide Installation manual Technical guide Installation instruction

035-17311-003-A-070432 Unitary Products GroupSUPPLY AIR DRIVE ADJUSTMENTAt unit start-up, the measured CFM may be higher or lowerthan the required CFM. To achieve the required CFM, thespeed of the drive may have adjusted by changing the datumdiameter (DD) of the variable pitch motor sheave asdescribed below:Required CFMMeasured CFMUse the following tables and the DD calculated per the aboveequation to adjust the motor variable pitch sheave.EXAMPLEA 12.5 ton unit was selected to deliver 4,000 CFM with a 3HP motor, but the unit is delivering 3,800 CFM. The variablepitch motor sheave is set at 2 turns open.Use the equation to determine the required DD for the newmotor sheave,4,000 CFM3,800 CFMUse Table 31 to locate the DD nearest to 4.21 in. Close thesheave to 1 turn open.New BHP3= (Speed increase) • BHP at 3,800 CFM3= (Speed increase) • Original BHP= New BHPNew motor Amps3= (Speed increase) • Amps at 3,800 CFM3= (Speed increase) • Original Amps= New AmpsFIGURE 23 - DRY COIL DELTA PBefore making any blower speed changes reviewthe installation for any installation errors, leaks orundesirable systems effects that can result in loss ofairflow.Even small changes in blower speed can result insubstantial changes in static pressure and BHP.BHP and AMP draw of the blower motor willincrease by the cube of the blower speed. Staticpressure will increase by the square of the blowerspeed. Only qualified personnel should make blowerspeed changes, strictly adhering to the fan laws.( ) • 4.0 in. = 4.21 in.( ) • Existing DD = New DD