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356214-XIM-A-0108
34 Johnson Controls Unitary Products
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 AIR SUPPLY 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.
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