1 HVAC&R CONTROLS by Jayson Goff, CM 12/12/2012
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OBJECTIVES• Understand the operation of relays and
contactors
• Explain how to test relays and contactors
• Learn the selection and application of transformers
• Find out how to troubleshoot pressure controls
• Understand the operation of solenoids
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Transformer Types
Transformer Types
• Boost-and-buck transformers
• Control transformers
• Auto-transformers
• High-current secondary transformers
“Boosting” transformer
“Bucking” transformer
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Setting the Low-Pressure Control
Step 1. Set HIGH EVENT by adjusting range screw.All-Range Controls:
•Turn screw clockwise to raise high event.Micro-Set Controls: •Turn screw clockwise to lower CUT IN setpoint.
Step 2. Adjust the differential screw.All-Range Controls: •turning the differential screw changes theLOW EVENT
•Turn screw clockwise to raise low eventMicro-Set Controls: •Turning the differential screw changes the differential setting.•Turn screw clockwise to increase differential
DifferentialScrew
Range Screw
Visible Pressure Scale