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177820-YIM-A-0506
26 Unitary Products Group
PHASING
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 misphased.
Change the incoming line connection phasing to obtain
proper rotation. (Scroll compressors operate in only
one direction. If the scroll is drawing low amperage,
has similar suction and discharge pressures, or pro-
ducing a high noise level, the scroll is misphased).
SUPPLY AIR BLOWERS
These blowers have either 3-speed direct drive motors,
or single speed motors equipped with a belt drive. Belt
drive units have a variable pitch motor pulley that
allows the blower speed to be adjusted.
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 motor speed
tap (direct drive) or the motor pulley number of turns
open (belt drive) can be determined from the Blower
Performance 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 12.
TABLE 20: STATIC RESISTANCES
1000 1200 1400 1600 1800 2000 2200 2400 2600
0.07 0.08 0.09 0.11 0.13 0.15 0.17 0.20 0.23
5-15KW 0.04 0.05 0.06 0.07 0.08 0.10 0.12 0.14 0.16
20-30KW 0.06 0.07 0.08 0.09 0.11 0.13 0.15 0.17 0.20
0.06 0.07 0.08 0.09 0.10 0.11 0.12 0.14 0.16
BOTTOM DUCT CONNECTIONS
1
ELECTRIC
HEATERS
1
RESISTANCE, IWG
CFM
DESCRIPTION
ECONOMIZER
1, 2
1. Deduct these resistance values from the available external static pressure shown in SUPPLY AIR BLOWER PERFORMANCE Tables.
2. The pressure through the economizer is greater for 100% outdoor air than for 100% return air. If the resistance of the return air
duct system is less than 0.25 IWG, the unit will deliver less CFM during full economizer operation.
Scroll compressors require proper rotation to
operate correctly. Do not change the internal
wiring to make the blower, condenser fans, or
compressor rotate correctly. Change the
incoming power to the main terminal block to
obtain proper rotation.
FIGURE 12 - BELT ADJUSTMENT