284806-YIM-A-0107
Unitary Products Group
39
PHASING
YORK
®
MODEL DM, units are properly phased at the
factory. Check for proper compressor rotation. If the
blower or compressors rotate in the wrong direction at
start-up, the electrical connection to the unit is mis-
phased. Change the incoming line connection phasing
to obtain proper rotation. (Scroll compressors operate
in only one direction. If the scroll is drawing low amper-
age, has similar suction and discharge pressures, or
producing a high noise level, the scroll is misphased).
CHECKING SUPPLY AIR CFM
The RPM of the supply air blower will depend on the
required CFM, the unit accessories or options and the
static resistances of both the supply and the return air
duct systems. With this information, the RPM for the
supply air blower and the motor pulley adjustment
(turns open) can be determined from the Blower Per-
formance Data Tables.
High speed drive accessories (containing a smaller
blower pulley and a shorter belt) are available for appli-
cations requiring the supply air blower to produce
higher CFM's and/or higher static pressures. Use
Model 1LD0416 for 15 ton units, Model 1LD0417 for 20
ton units, and Model 1LD0435 for 25 ton units. Refer to
the Blower Motor and Drive Data Table 23.
Note the following:
1.
The supply air CFM must be within the limitations
shown in the Unit Application Data Table 1.
2.
Pulleys can be adjusted in half turn increments.
3.
The tension on the belt should be adjusted as
shown in the Belt Adjustment Figure 17.
Scroll compressors require proper rotation to
operate correctly. Units are properly phased at
the factory. Do not change the internal wiring to
make the blower, condenser fans, or compres-
sor rotate correctly.
FIGURE 17 - BELT ADJUSTMENT
