035-13329-001-B-0504
16
Unitary Products Group
TWO-STAGE HEATING:
a.
If the fan switch is in the “ON” position, the evapora-
tor blower motor relay (BR) will be energized
through terminal G to provide continuous blower
operation. If the fan switch is in the “AUTO” position,
the blower will operate only when there is a call for
heating by the thermostat.
b.
Upon a call for first-stage heat by the thermostat, the
first stage of heat will be energized.
c.
The thermostat will cycle the electric heat to satisfy
the heating requirements of the conditioned space.
CONTINUOUS BLOWER - Continuous blower operation is
possible by closing the R to G circuit on the thermostat.
HEAT ANTICIPATOR SETPOINTS
It is important that the anticipator setpoint be correct. Too
high of a setting will result in longer heat cycles and a greater
temperature swing in the conditioned space. Reducing the
value below the correct setpoint will give shorter “ON” cycles
and may result in the lowering of the temperature within the
conditioned space. Refer to Table 8 for the required heat
anticipator setting.
CHECKING SUPPLY AIR CFM
The speed of the supply air blower will depend on the
required CFM, the unit accessories and the static resistances
of both the supply and the return air duct systems. With this
information, the speed for the supply air blower can be deter-
mined from the static resistance and blower performance
data on Tables 3 thru 5.
Knowing the required blower RPM and the blower motor HP,
the speed setting for the direct-drive supply air motor can be
determined.
The setting (turns open) for the belt-drive supply air motor
pulley can be determined from Table 9.
BELT-DRIVE BLOWER
All units with belt-drive blowers have single-speed motors.
The variable pitch pulley on the blower motor can be adjusted
to obtain the desired supply air CFM.
Refer to Table 6 for blower motor and drive data. The tension
on the belts should be adjusted as shown in Figure 7.
Start the supply air blower motor. Adjust the resistances in
both the supply and the return air duct systems to balance
the air distribution throughout the conditioned space. The job
specifications may require that this balancing be done by
someone other than the equipment installer.
To check the supply air CFM after the initial balancing has
been completed:
TABLE 8: HEAT ANTICIPATOR SETTING
NOMINAL
HEATER
SIZE KW
VOLTAGE
SETTING, AMPS
TH1
TH2
5
7
10
15
20
30
240-3-60
0.35
0.35
0.35
0.35
0.35
0.35
-
-
-
0.19
0.38
0.38
7
10
15
20
30
480-3-60
0.35
0.35
0.35
0.37
0.37
-
-
-
0.29
0.29
TABLE 9: BELT DRIVE SUPPLY AIR ADJUSTMENT
MOTOR PULLEY ADJUSTMENT
TURNS
OPEN
*
*.
Pulley can be adjusted in half-turn increments.
BLOWER DRIVE RANGE (RPM)
3 TONS
4 TON
5 TON
5
780
790
850
4
842
856
924
3
904
922
998
2
966
988
1072
1
1028
1054
1246
0
1090
1120
1220
FIGURE 7 - BELT ADJUSTMENT
SPAN LE
NGTH
DEFL FO
RCE
* NEVER LOOSEN
(A)
(C)*
(D)
CAUTION
Procedure for adjusting belt tension:
1. Loosen nut (D) from the motor mount.
2. Never loosen nuts (C) from each other while loosening nut (D).
3. Adjust the tension by turning bolt (B).
4. Do not loosen the four nuts (top and bottom) (A); unless additional tensioning
distance is required; immediately re-tighten these bolts if loosened.
5. Use a belt tension checker to apply a perpendicular force to one belt at the
midpoint of the span as shown. The deflection force should be applied
until a specific deflection distance of 4mm (5/32")is obtained. To determine
the deflection distance from normal position, use a straight edge from
sheave to sheave as a reference line. The recommended deflection force
is as follows:
Tension new belts at the max. deflection force recommended for the belt
section. Check the belt tension at least two times during the first 24 hours of
operation. Any re-tensioning should fall between the min. and max.
deflection force values.
6. After adjusting, re-tighten nut (D) against the motor mount taking care not
to loosen nuts (C).
(B)
