SECTION IX: SAFETY CONTROLS
CONTROL CIRCUIT FUSE
A
BLOWER DOOR SAFETY SWITCH
Main power to the unit must still be interrupted at the main power disconnect switch before any service or repair work is to be done to the unit. Do not rely upon the interlock switch as a main power dis- connect.
Blower and burner must never be operated without the blower panel in place.
This unit is equipped with an electrical interlock switch mounted in the burner compartment. This switch interrupts all power at the unit when the panel covering the blower compartment is removed.
Electrical supply to this unit is dependent upon the panel that covers the blower compartment being in place and properly positioned.
ROLLOUT SWITCH CONTROLS
These controls are mounted on the burner assembly. If the temperature in the area surrounding the burner exceeds its set point, the gas valve is
PRESSURE SWITCHES
This furnace is supplied with a pressure switch, which monitors the flow through the combustion air/vent piping system. This switch
1.Blockage of vent piping or terminal.
2.Failure of combustion air blower motor.
LIMIT CONTROLS
There is a high temperature limit control located on the furnace vesti- bule panel near the gas valve. This is an automatic reset control that provides over temperature protection due to reduced airflow. This may be caused by:
1.A dirty filter.
2.If the indoor fan motor should fail.
3.Too many supply or return registers closed or blocked off.
The control module will lockout if the limit trips 5 consecutive times. If this occurs, control will reset & try ignition again after 1 hour.
Heating Cycle
When the thermostat switch is set on HEAT and the fan is set on AUTO, and there is a call for heat, a circuit is completed between terminals R and W of the thermostat. When the proper amount of combustion air is being provided, the pressure switch will close, the ignition control pro- vides a
If the flame is not detected within 7 seconds of the gas valve opening, the gas valve is shut off and a retry operation begins. Also, if the flame is lost for 2 seconds during the
A momentary loss of gas supply, flame blowout, or a faulty flame probe circuit will result in a disruption in the flame and be sensed within 1.0 seconds. The gas valve will
During burner operation, a momentary loss of power for 50 milliseconds or longer will
Hot Surface Ignition System
HOT SURFACE IGNITION SYSTEM
Do not attempt to light this furnace by hand (with a match or any other means). There may be a potential shock hazard from the components of the hot surface ignition system. The furnace can only be lit automatically by its hot surface ignition system.
SEQUENCE OF OPERATION
The following describes the sequence of operation of the furnace. Refer to Owners Manual for component location.
Continuous Blower
Cooling/heating thermostats have a fan switch that has an ON and AUTO position. In the ON position the thermostat circuit is completed between terminals R and G. The motor will operate continuously on the speed tap wire that is connected to the “HI COOL” cooling terminal on the control board. To obtain a constant air circulation at lower flow rate, change the
Intermittent Blower - Cooling
Cooling/heating thermostats have a fan switch that has an ON and AUTO position. In the AUTO position the thermostat circuit is completed between terminals R and G when there is a call for cooling. The motor will operate on the speed tap wire that is connected to the “HI COOL” cooling terminal on the control board. The fan off setting is fixed at 60 seconds to improve cooling efficiency.
TROUBLESHOOTING
The following visual checks should be made before troubleshooting:
1.Check to see that the power to the furnace and the ignition control module is ON.
2.The manual
3.Make sure all wiring connections are secure.
4.Review the sequence of operation. Start the system by setting the thermostat above the room temperature. Observe the system’s response. Then use the troubleshooting section in this manual to check the system’s operation.
Never bypass any safety control to allow furnace operation. To do so will allow furnace to operate under potentially hazardous condi- tions.
Do not try to repair controls. Replace defective controls with UPG Source 1 Parts.
Never adjust pressure switch to allow furnace operation.
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