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NORA Oilheat Technicians Manual

resistor in place, the cad cell relay is operating as designed and the problem is with the cad cell flame detector. With the unit operating, connect the cad cell leads to your ohmmeter. A reading of zero ohms indicates a short circuit. Check for pinched or shorted cad cell wires. If the resistance is infinite, check for broken cad cell wires or a loose or defective cell. On most properly adjusted burners, the reading will be 400 ohms or less. Some burners with large static plates or small openings in the retention head operate in the 400-800 ohm range. Very few burners operate with resistance over 800 ohms. If the reading is greater than 1600 ohms, there is a serious problem with the fire, the cad cell eye, its holder, its leads or its alignment. Remember the cad cell needs to have a good view through the air tube to the fire. If the eye is coated with soot, it will not be able to “see” the flame. Clean the eye and continue your troubleshooting to find out why the eye is dirty. Chapter 11 Primary Controls Ohmmeter Cad Cell Check List Ohmmeter Reading Cause Action 0 ohms Short circuit Check for pinched cad cell leadwires Less than 1660 ohms Cad cell and application None but not zero are working correctly Over 1600 ohms Dirty or defective cell, 1. Clean cell face, recheck but not infinite improper sighting or 2. Check flame sighting improper air adjustment 3. Replace cell, recheck 4. Adjust air band to get good reading Infinite resistance Open circuit Check for improper wiring, loose cell in holder or defective cell Chapter 11—Primary Controls 11-11 Burner Locks Out On Safety Check Primary Control Check Cad Cell With Ohmmeter Without Ohmmeter Check Resistance Clean Cell Check Wiring Check Flame Adjustment Checking Cad Cell and Primary Air Ignition Tube Electrode Nozzle Blower Primary Control Remove Lead Wires From Primary Control Start Burner Jumper F-F (With 1500 Resistor) Control Locks Out—Replace— Burner Runs—Trouble is Cad Cell Check Resistance— Infinite—Open Circuit (Cell Defective or Not Seated) Greater Than 1600 Ohms—Cell Dirty or Not Sighting Properly


NORA Oilheat Technicians Manual
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