2019 Cengage CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES INTRODUCTION • Most troubleshooting involves a specific problem the customer is encountering • Sometimes exact trouble is difficult to locate but relatively simple once narrowed down • First step in troubleshooting any component is to understand its operation and function © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Electric Motors • Overview • Electric motors are the most important loads • Used almost exclusively to cause rotating motion • Many different types • Type used will have no effect on diagnosing the condition • Will have a great effect on selection of a replacement motor © 2019 Cengage

TROUBLESHOOTING ELECTRIC CONTROL DEVICES CHAPTER 14 Electric Motors • Open-type electric motors • Failure

TROUBLESHOOTING ELECTRIC CONTROL DEVICES CHAPTER 14 Electric Motors • Sealed motors • No internal parts, other than bearings • Only part that can be checked • Windings • Diagnosing bearing failure • Often difficult • No visual inspection © 2019 Cengage

TROUBLESHOOTING ELECTRIC CONTROL DEVICES CHAPTER 14 Contactors and Relays • Overview • Used for operation of loads • Same procedure is used to check both • Common problems • Contacts • Coil • Mechanical linkage © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Contactors and Relays • Contacts • Must make good direct contact when energized • Checking a set of contacts • • Visual inspection Resistance check Voltage check Contact alignment © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Contactors and Relays • Coil • Used to close the contacts • Creates a magnetic field that pulls the plunger into the magnetic field • Should be checked for opens, shorts, or a measurable resistance © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Contactors and Relays • Mechanical linkage • Can cause malfunctions • • Sticking contacts Contacts that do not close due to excess friction Contacts that do not make good contact Misalignment of contacts • Visual inspection © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Overloads • Overview • Most major loads have some type of overload protection • Often overlooked as being a problem • High cost of major loads • Necessary to protect them © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Overloads • Fuse • Easy type of overload

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Overloads • Circuit breaker • Trips or opens on an overload • Must be manually reset • Checked by taking a voltage reading on the load side of the circuit breaker © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Overloads • Line voltage overload • Installed on a load device • Easiest type of overload to check • Can be: • Open • Permanently closed • Open on a lower-than-rated ampere draw © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Overloads • Pilot duty overload • Set of contacts will open if an overload occurs in line voltage side • Line voltage feeds directly through a current sensing element, then to the load • Line voltage section can be controlled by heat, amperage, or magnetism • Pilot duty contacts: easily checked by an ohmmeter © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Overloads • Internal overloads • Used in hermetic compressors • Actually embedded in the windings • Faster response to overloads • Hard to check • No external connections • Extremely hard to diagnose for troubles © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Thermostats • Basic types • Line voltage thermostat • Makes or breaks line voltage to a load • Only function is to open or close a set of contacts • Low-voltage thermostat • Used when a voltage lower than 120 is used • Many functions © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Thermostats • Line-voltage thermostats • Easy to troubleshoot • Could have two, three, or four terminals • Be sure contacts are closed in the correct temperature range • Control voltage can be checked at the equipment © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Thermostats • Low-voltage thermostat • More difficult to troubleshoot • Operates many functions • • • System heating and cooling Fan motor with heating and cooling operations Fan motor independently Two-stage systems Damper motors Pilot function of a gas heating system © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Pressure Switches • Start or stop some electric load • When pressure indicates • Used as safety devices or operating controls • Stop electric load when pressure reaches an unsafe condition • Excessive discharge pressure • Low suction pressure © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Pressure Switches • Importance troubleshooting aspects • Understand use • Determine if it should be open or closed • Possible problems • Pressure switch is faulty • System is malfunctioning © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Transformers • Raise or lower incoming voltage by induction • Some are used to buck (lower) or boost (raise) incoming voltage • Buck-and-boost transformer • Checked in two ways: • Resistance • Voltage check © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Electric Heating Controls • Sequencer and contactor • Control operation • Electric resistance heaters and other applications • Many other components • Thermostats • Electric motors • Sequencers © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Gas Heating Controls • Overview • Many thermostats are used in gas heating control circuits • Open or close on rise in temperature • Limit switches • Can be line or low voltage • Generally have only one function © 2019 Cengage

TROUBLESHOOTING ELECTRIC CONTROL DEVICES CHAPTER 14 Gas Heating Controls • Gas valves • Available in many different designs • Commonly used gas valves • Combination and redundant-type • Troubleshooting • Know the type of gas valve used • Understand gas valve operation © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Gas Heating Controls • Troubleshooting intermittent pilot systems • Checking the intermittent ignition module poses a fire or explosion hazard • Turn off when a gas leak is suspected or gas is smelled • Do not light pilot or appliance while spilled gas remains • Perform a gas leak inspection © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Gas Heating Controls • Troubleshooting direct ignition control systems • Checking the operation of a direct ignition module poses a fire or explosion hazard • Turn off when a gas leak is suspected or gas is smelled • Do not light pilot or appliance while spilled gas remains • Perform a gas leak inspection © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Gas Heating Controls • Troubleshooting integrated furnace controls • Furnace control board • Self-diagnosis feature • Troubleshooting • Understand control sequence • Determine problem • Locate and repair problem © 2019 Cengage

TROUBLESHOOTING ELECTRIC CONTROL DEVICES CHAPTER 14 Oil Heating Controls • Overview • Thermostats • Used as operating controls • Stop and start • Primary controls • Stack switch • Cad cell control © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Oil Heating Controls • Troubleshooting stack switch primary controls • Safety checks • Flame failure • Ignition or fuel failure • Power failure • Burner • Must be in satisfactory operating condition © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES Oil Heating Controls • Troubleshooting cad cell primary controls • Cad cell should view the flame directly • Oil burner and components must be in good condition • Check power supply to primary control and all limit switches • Faulty cad cell could allow the burner to operate even without seeing a flame © 2019 Cengage

CHAPTER 14 TROUBLESHOOTING ELECTRIC CONTROL DEVICES SUMMARY • Most heating, cooling, and refrigeration technicians are required to do some diagnosing of components • Technicians must understand how components work, how to use and check electric meters, checking procedures for electric components • Safety is the utmost importance when troubleshooting © 2019 Cengage