14.Blower Motor and Drive (cont'd)
Adjusting Blower Speed
The blower speed may be adjusted to achieve the desired outlet tem- perature, as long as the adjustment is within the temperature rise and the static pressure limits shown on the heater rating plate. Direct drive motors are factory set at medium speed for heating and high speed for cooling (if ordered). Belt drive motors are factory set between maxi- mum 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 activate. Re- ducing the blower speed will correct these conditions. If ductwork is added to an installation, it may be necessary to increase the blower speed.
Direct drive motors have
1.Turn off the gas and electric power.
2.Remove the blower door panel.
3.Consult the wiring diagram on the heater and follow the chart below to choose the wiring for the desired adjustment. Units are wired at high speed for cooling (if ordered) and medium speed for heating.
Model Sizes |
| Speed |
| Use these two motor wires: | |
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150, 200, 250, 350 |
| High |
| White and Black | |
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| Medium | White and Blue |
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| Low | White and Red |
300 and 400 |
| High |
| White and Black | |
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| Medium |
| White and Blue | |
4.Cut the crimped cap for the end of the wire that you intend to use and strip the insulation.
5.Disconnect the
6.Put a wire nut on the end of the blower motor wire that was discon- nected.
7.Replace the heater door panel. Turn on the gas and electric. Check for proper operation.
Belt drives have an adjustable pulley which permits adjustment of the blower speed. Follow these instructions to adjust blower speed.
1.Turn off the gas and the electric power.
2.Loosen belt tension and remove the belt.
3.Loosen the set screw on the side of the pulley away from the motor.
4.To increase the blower speed, turn the adjustable half of the pul- ley inward. To decrease the blower speed, turn the adjustable half of the pulley outward. One turn of the pulley will change the speed
5.Tighten the set screw 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". (See Figure 16.)
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.
Motor Amps
Use an amp meter to check motor amps. The chart lists full load amps for various HP's and voltages. Amps may be adjusted downward by reducing blower RPM or increasing duct system static pressure.
The chart below can be used for sizing line wiring but should not be interpreted as the exact motor amps. See the motor rating plate for exact
motor specifications. At final adjustment, amperes should not ex- ceed motor nameplate amp rating. The installation must be ad- justed to obtain a temperature rise within the range specified on the heater rating plate.
Full Load Amps - Blower Motors (Open)
HP |
| 1/4 | 1/3 |
| 1/2 | 3/4 | 1 | 2 | 3 | 5 | |
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230V | 1PH |
| 6.3 | ||||||||
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| Optional Belt Drive Motors |
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208V | 1 PH | 2.1 | 3.2 |
| 5.1 | 6.3 | 7.5 | 8.3 | 10.0 | ||
230V | 1PH | 2.3 | 2.8 |
| 4.4 | 5.5 | 6.5 | 7.5 | 10.2 | ||
208V | 3 PH | 1.1 | 1.4 |
| 3.0 | 2.9 | 3.7 | 5.6 | 7.0 | 9.0 | 13.4 |
230V | 3PH | 1.4 | 1.6 |
| 2.5 | 2.6 | 3.2 | 5.0 | 6.6 | 8.6 | 13.2 |
460V | 3PH | 0.75 | 0.8 |
| 1.0 | 1.3 | 1.6 | 2.7 | 3.5 | 4.3 | 6.6 |
575V | 3PH |
| 1.1 | 1.6 | 2.1 | 3.6 | 5.4 | ||||
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CAUTION: An external duct system static pressure not within the limits shown on the rating plate, or improper motor pulley or belt adjustment, may overload the motor or cause the limit control to activate. See Hazard Levels, page 2.
15. Gas Valve
The main operating gas valve is powered by the
WARNING: The operating valve is the prime safety shutoff. All gas supply lines must be free of dirt or scale before connecting the unit to ensure positive closure. See Hazard Levels, page 2.
16. Ignition System
This heater is equipped with a direct spark integrated control system. The system monitors the safety devices and controls the operation of the blower and venter motors and the gas valve.
Ignition System Operating Sequence
On a call for heat from the thermostat, the system energizes the venter motor and goes through a
The gas valve is then energized, and the ignition system provides the high voltage spark to the electrode to ignite the main burner gas. Burner flame is electronically sensed by the control (minimum 1.0 microamps) upon carryover of all burners. (A separate solid metal probe is used as the flame sensing function. A low voltage electrical signal is imposed on the metal probe which is electrically isolated from ground. When the flame impinges on the flame sensing probe, the flame acts as a conduc- tion path to ground. The flame rectifies and completes the DC circuit, and the ignition system acknowledges the flame.)
The blower motor is energized by the system after 30 seconds of flame sensing.
After the thermostat has been satisfied, the system
NOTE: This is a three trial system. The unit will lockout for one hour before initiating another trial for ignition. If the unit fails after one recycle interval, the unit will go into hard lockout and must be reset by interrupting power or resetting the thermostat. To initiate another trial for ignition before the one hour interval, either reset the thermostat or interrupt power to the unit for 30 seconds.
Form 405, Page 16