Form I-XE/CRGB/RPB, Page 24
WARNING: If you turn off the power supply, turn
off the gas. See Hazard Levels, page 2.
15. Limit and Energy Cutoff
Controls
Heaters are equipped with a non-adjustable high limit switch which
shuts off the gas in the event of motor failure, lack of air due to dirty
filters, or restrictions at the inlet or outlet of the unit. See Paragraph 30
for limit control check. For location, see
FIGURE 19
, Item 11.
Indoor Model XE systems are also equipped with a fusible link in the
thermocouple circuit which acts to cause safety pilot drop out in case
of limit control malfunction or failure of the blower motor in combina-
tion with the automatic valve failing to close. This ECO control acts as
a super high limit providing redundant safety control and is calibrated
to open at a much higher temperature than the standard automatic
reset limit.
An ECO fusible link interruption can be caused by the following
combination of failures:
1. Automatic gas valve stuck in open position.
2. Restricted air flow over heat exchanger due to motor failure,
broken blower belt, or defective fan control.
3. Ruptured gas pressure regulator.
4. Improper wiring.
WARNING: An ECO circuit interruption is a major
failure caused by a malfunction of the primary safety
13. Blowers, Belts and Drives
Check belt tension. Proper
belt tension is important to
the long life of the belt and
motor. A loose belt will cause
wear and slippage. Too much
tension will cause excessive
motor and blower bearing
wear. Adjust the belt tension
by turning the adjusting screw on the motor base until the belt can be
depressed 3/4" (19mm). (See
FIGURE 20
.) After correct tension is
achieved, re-tighten the locknut on the adjustment screw. Be sure that the
belt is aligned in the pulleys.
Adjusting Blower Speed
The blower speed may be adjusted to achieve the desired outlet tempera-
ture, as long as the adjustment is within the temperature rise and the static
pressure limits shown on the furnace rating plate. Motors are factory set
between maximum and minimum blower speeds.
If the duct resistance is low, the blower may deliver too high an air
volume. If the resistance is very low, the blower may deliver excess air to
overload the motor, causing the overload protector to cycle the motor.
Reducing the blower speed will correct these conditions. If ductwork is
added to an installation, it may be necessary to increase the blower speed.
Decreasing blower speed will increase outlet temperature; increasing blower
speed will decrease outlet temperature.
At final adjustment, amperes should not exceed motor nameplate
amp rating. The installation must be adjusted to obtain a tempera-
ture rise within the range specified on the furnace rating plate.
The belt drive on these units is equipped with an adjustable pulley which
permits adjustment of the blower speed. Follow these instructions to
adjust the blower speed.
1.
Turn off the gas and the electric power.
2. Loosen belt tension and remove the belt.
3.
Loosen the setscrew on the side of the pulley away from the motor.
4. To increase the blower speed, decreasing outlet temperature
,
turn the adjustable half of the pulley inward.
To decrease the blower
speed, increasing the outlet temperature
, turn the adjustable half
of the pulley outward. One turn of the pulley will change the speed 8-
10%.
5.
Tighten the setscrew on the flat portion of the pulley shaft.
6.
Replace the belt and adjust the belt tension. Adjust tension by turning
the adjusting screw on the motor base until the belt can be depressed
3/4" (19mm). See
FIGURE 20
. Re-tighten the lock nut on the adjust-
ing screw. Be sure that the belts are aligned in the pulley grooves
properly and are not angled from pulley to pulley.
7.
Turn on the gas and electric. Light the heater following the instruc-
tions on the lighting instruction plate.
8.
Check the motor amps with an amp meter. The maximum motor amp
rating on the motor nameplate must not be exceeded.
When service is complete, check for proper operation.
Blower Rotation
Each blower housing is marked for proper rotation. Rotation may be
changed on single-phase motors by re-wiring in the motor terminal box.
Three-phase motors may be reversed by interchanging two wires on the
3-phase supply connections.
Optional Airflow Proving Switch (Makeup Air
only) - Outdoor Models with Option BW1
The optional airflow proving switch ensures that the circulating air blower
is functionally providing an adequate amount of airflow prior to the unit
being fired. The switch is a single pole/normally open device which closes
when an increase in pressure, above the setpoint, is sensed in the circulat-
ing air blower. The switch is located in the blower junction box. (See
FIGURE 19
, Item 40).
Contacts are set to close at .10" w.c. (+.05" or -.02" w.c.).
3/4 (19mm)
FIGURE 20 - Check Belt Tension
14. Blower Motors
Use an amp meter to check motor amps. The following chart lists full
load amps for various HP's and voltages. Amps may be adjusted down-
ward by reducing blower RPM or increasing duct system static pres-
sure.
This chart can be used for sizing line wiring but should not be inter-
preted as the exact motor amps. See the motor rating plate for exact
motor specifications.
Full Load Amps - Blower Motors (Open)
(Single Speed- Average Values)
HP
1/4 1/3 1/2 3/4
1
1-1/2
2
3
5
115V 1PH
5.1
5.5
8.8 11.0 13.0 15.0 20.4 24.8 N/A
208V 1PH
2.1
3.2
5.1
6.3
7.5
8.3
11.3 14.0 28.0
230V 1PH
2.3
2.8
4.4
5.5
6.5
7.5
10.2 12.4 26.0
208V 3PH
1.1
1.4
2.3
2.9
3.7
5.6
7.0
9.0 13.4
230V 3PH
1.4
1.6
2.0
2.6
3.2
5.0
6.6
8.6 13.2
460V 3PH
.75
.80
1.0
1.3
1.6
2.7
3.5
4.3
6.6
575V 3PH
N/A N/A N/A N/A 1.1
1.6
2.1
3.6
5.4
Optional Variable Frequency Drive
When an optional variable frequency drive is ordered, the motor oper-
ates on two speeds as determined by the electrical frequency. High
speed is used for cooling and low speed for heating. 60 hertz is the
maximum high speed. Maximum speed for low speed heating is the
frequency that will provide the maximum temperature rise of the heater.
Follow the variable frequency controller manufacturer's instructions
that are packaged with the heater (in the owner's envelope) to program
the variable frequency drive settings. The formula for motor speed is
N=120xf/p where N is speed; f is frequency; and p is number of poles
(3600 RPM motor has 2 poles; an 1800 RPM motor has 4 poles).
Example:
1800 RPM motor on 60Hz; N = 120 x 60/4 = 1800
1800 is synchronous speed; assume 2% slip. Motor
will run between 1750 and 1790 RPM at full load
depending on design. Run the same motor at 45Hz
(120 x 45/4 = 1350). 1350 RPM less 2% slip equals
about 1300 RPM.
