Electrical Components

1. Electrical Components

2. Electrical ComponentsLesson Objectives • Principles of electricity • Types of motors • Compressors • Relays, contactors and starters • Capacitors • Transformers • Thermostats • Safety controls • Defrost controls • Electrical heaters • Miscellaneous controls

3. Introduction • The work done by any vapor-compression system is accomplished through the use of components operated by electric power. • Connecting wires form circuits that provide paths for electric current: • Any interruption in the electric circuits will cause the system to fail to operate as it is designed to do. • A thorough understanding of the key electrical components that make up these systems is required. • You must have a good working knowledge of the principles of electricity.

4. Voltage • Electrical pressure. • Electromotive force: • “E” in ohms law calculation: • It takes 1 volt (1 V) to push 1 amp (1 A) through 1 ohm (1Ω) of resistance.

5. Current • Movement of electrons in a conductor. • Measured in amperes. • Intensity: • “I” in ohms law calculation.

6. Resistance • Opposition to the flow of current. • Measured in ohms. • “R” in ohms law calculations.

7. Power • Rate of doing work. • Measured in watts. • “P” in calculations. • Power factor must be applied for inductive loads: • True power (watts) ÷apparent power (VA).

8. Loads • Components that consume power to do useful work. • Voltage drop is measure by connecting the voltmeter in parallel to the energized load.

9. Switches • Pass power through without consuming power. • No voltage drop (0 volts) will be measured across a closed switch supplying power to an operating load. • A voltage drop measured when connected in parallel across a switch indicates an open switch. • A voltage reading across a switch also could indicate bad contacts (usually less than full voltage).

10. Power Source • Electric power to the building. • Single-phase. • Three-phase. The power source is the generating facility that supplies electric power to the building. The power supplied may be either single-phase or three-phase.

11. Path • Wires and components that complete the circuit. • From the power source to the load and back to the source. The interconnecting wires and components that make up an electric circuit form a path that allows current to travel from the power source through the load and back to the source again. A path from the power source to a load is not sufficient to operate the load. The path must return to the power source and complete the circuit in order for the load to operate.

12. Motors: Shaded Pole • Low starting torque. • Low efficiency. • Small loads such as fans. Small motors are used widely in HVACR systems. The shaded-pole motor has the lowest starting torque of any motor discussed in this section. This type of motor is relatively inexpensive and is used to operate very small fan blades connected directly to the motor shaft. The basic construction of a shaded-pole motor is relatively simple, since no start winding is present. The imbalance in the strength of the magnetic field needed to produce rotation is obtained by “shading” a portion of the run winding with a heavy copper wire or band. Shaded-pole motors are used in applications so small that they are rated in watts rather than in horsepower (hp). They are normally available in sizes ranging from 6 W to approximately 35 W.

13. Motors: Split Phase • Start and run winding: • Higher resistance in the start winding creates a phase shift to improve starting torque. • Medium starting torque. • Centrifugal switch is often used to take the start winding out of the circuit. • Capacitors are added in different configurations to improve efficiency (run cap.) and improve starting torque (start capacitor). A split-phase motor has a relatively low starting torque compared to motors used to handle larger workloads, but more torque than the shaded-pole motor. Split-phase motors range in size from 1⁄20 hp to about 1⁄2 hp. Split-phase motors are so named because a single power supply is split between two individual windings—the run winding and the start windings—to produce the torque needed to start the motor. The run winding is energized whenever the motor is operating. The start winding has a higher resistance than the run winding and is in the circuit only long enough to help get the motor started. In order for the motor to start, both windings must be energized. Current travels through the two windings at different rates, which creates a phase shift, or imbalance, needed to start the motor. A phase shift is measured in electrical degrees and is commonly referred to as the phase angle. If the run winding and the start winding were constructed and configured exactly alike, the phase angle would equal zero. The magnetic field would have no imbalance in this case and the motor would fail to turn. Larger phase angles produce more starting torque. A split-phase motor typically has a phase angle of approximately 30°. Once a split-phase motor is started, the start winding must be removed from the motor circuit. If it is not removed, damage to the start winding will occur. A commonly used device to take the start winding out of the circuit is the centrifugal switch. This switch opens and closes its contacts depending on the motor speed. The switch is normally closed and connected in series with the start winding. When the motor reaches 70% to 75% of its full-run speed, the contacts of the centrifugal switch open and remove the start winding from the circuit. The motor now operates on only the run winding. When the motor is de-energized and its speed decreases, the centrifugal switch closes in preparation for the next “ON” cycle.

14. Compressors • Typically the largest motor in the system. • Open drive: • Motor is external of refrigerant circuit. • Semi-hermetic: • Can be rebuilt. • Can be cooled by suction gas. • Hermetic: • Motors are cooled by the suction gas. • Motor burn out will contaminate system. • Cannot be repaired in the field. The component that consumes the most power in any vapor-compression system is the compressor motor. Compressors also are the most expensive component to replace. A motor used with an open compressor typically is connected to the compressor with pulleys and belts. In a hermetic compressor, the motor is housed in the same shell that contains the compressor. When the motor in a hermetic compressor burns out, acid from the motor failure contaminates the compressor lubricant. A semi-hermetic compressor also contains the compressor and motor in the same housing—however, semi-hermetic compressors can be disassembled and rebuilt. Hermetic compressors cannot be disassembled and repaired in the field. The hermetic compressor motors are generally cooled by suction gas returning to the compressor and directed across the windings . The semi-hermetic compressor can be cooled the suction gas being passed across the windings, air cooled or by a water coil wrapped around the motor housing.

15. Two-speed Compressors • Two-speed compressor motors can be used to more closely match the system output to the load. • Staging is based on deviation from setpoint of the room thermostat. Some compressors have single-speed motors, while others have variable-capacity capability. The staging of a two-speed compressor in a heat-pump application, for example, is based on deviation from the set-point of the room thermostat.

16. Compressor Cooling • Cooled by refrigerant vapor. • Hermetic compressors must never be run in a vacuum: • Heat cannot be dissipated and motor damage will result. Circulating refrigerant vapor is used to cool the motor in an operating hermetic compressor. You must never run a hermetic compressor in a vacuum. Heat generated by the operating motor cannot be dissipated in a vacuum and the motor windings will be damaged.

17. Ratings • RLA – Rated load amps. • MCC - Maximum continuous current: • Maximum current that won’t trip the overload. • The minimum RLA value that can be published by the manufacturer is the MCC divided by 1.6. The data plate on a unit shows the rated-load amperes (RLA) of the compressor. The RLA is a term defined by Underwriters Laboratories (UL). It is a number calculated after the compressor is tested with its motor protector in place, and has to do with the motor’s overload value. To determine the RLA, the manufacturer must operate the compressor at the rated frequency and at a current just below the point that will cause the motor protector to trip. The current that permits the compressor to operate and not trip the motor protector is called the maximum continuous current (MCC). The MCC value is used to determine the RLA. According to UL guidelines, the minimum RLA value that can be published by the manufacturer is the MCC divided by 1.6. The RLA, in turn, is used to select the contactor and wire size. The RLA also is used to set a crankcase pressure regulator—however, it is not used as an indicator of correct refrigerant charge.

18. Compressor Motors: PSC • Single phase. • Run capacitor is connected between run and start windings. • Applied to systems that have rapid pressure equalization on shutdown. Compressor motors may be either single-phase or three-phase motors. Single-phase motors used in compressors are permanent split-capacitor (PSC) motors. A run capacitor is used to increase a shift in the phase angle and provide better starting and running characteristics. The run capacitor is connected between the run and start terminals of the motor, as shown in this slide. A run capacitor can create a maximum shift in phase angle of 90°. However, a more typical shift in phase angle is approximately 75°. Three-phase motors do not use capacitors.

19. Compressor Motors: CSCR • Start and run capacitors are used. • Both are in the circuit during start-up. • Start relay opens when motor gets up to speed. • Run capacitor remains in the circuit. Capacitor-start, capacitor-run (CSCR) compressor motor circuits utilize both start capacitors and run capacitors. The start relay is a potential relay with normally closed contacts. See the image shown in this slide, and note that the start-relay contacts and the start capacitor are connected in series with the start winding. When voltage is applied to the circuit, the run and start capacitors are connected in parallel for high starting torque. Voltage across the start winding increases as the motor shaft speed increases. The start-relay coil is connected in parallel with the start winding. The coil terminals are connected to the start and common terminals of the compressor. The start relay can “sense” the motor speed by the rising voltage impressed on the start winding. When the motor shaft reaches sufficient speed, the start relay opens the circuit to the start capacitor. The run capacitor remains in the circuit while the motor is running. A CSCR motor that has an open run capacitor may start, but it will draw a higher-than-normal running current. If a CSCR motor hums momentarily and then shuts down on internal overload during start-up, the potential relay coil is most likely defective.

20. ECM • Electrically Commutated Motor: • Electronically controlled brushless DC motor. • Used primarily on blower motors at the present time: • Provides excellent humidity control; • Factory-set airflow; • Energy-efficient operation; • Long life; • Low operating temperature; • Programmability; and • Wide operating range.

21. ECM • Motors used to drive fans and blowers in HVACR applications can be single-speed, multi-speed or electronically commutated motors. An electronically commutated motor (ECM) is used to provide variable-speed capability for better humidity and temperature control within a conditioned space. The ECM is a brushless dc motor with a built-in inverter and a microprocessor-based motor controller, as shown in this slide. Several features make ECMs superior to conventional electric motors, including: • Factory-set airflow; • Energy-efficient operation; • Long life; • Low operating temperature; • Programmability; and • Wide operating range. • Due to the motor’s factory-programmed setpoints, the fan flow remains constant regardless of external static pressure. The ECM adjusts speed and torque automatically to maintain the design air flow volume. The ball-bearing design and low operating temperature of the ECM mean that an air handler or furnace blower can be operated at lower minimum speeds than are possible with conventional motors. This results in a wide air flow range for each size unit. • The ECM has a minimum efficiency of 70% throughout its entire operating range. Conventional induction motors become less efficient at the reduced speeds that are typically selected for fan-powered applications. Energy savings of 50% to 60% can be achieved with ECMs at normal operating conditions.

22. Air Flow • Air flow delivered from the fan is directly proportional to the speed of the fan. • Residential systems most commonly use forward pitched blades. • Multi-tap motors reduce speed because the horsepower is reduced and it can not keep up with the load: • It is important to match the horsepower when replacing the motor. A larger hp motor will not slow down. The air flow (in cfm) delivered by a blower changes proportionately to the change in motor speed (in rpm). For example, when motor rpm is doubled, air flow cfm is doubled. Likewise, when motor rpm is decreased by 50%, air flow cfm decreases by 50%. The blower wheel used by a direct-drive blower has an rpm equal to that of the motor. Forward-curved centrifugal fans are most commonly used in residential systems. Changing the connected tap on a multi-speed motor that is driving a supply blower changes the cfm delivered by the blower. When selecting a replacement indoor blower motor, make sure that the horsepower of the replacement matches that of the original motor.

23. Motors • The outdoor unit of residential systems typically use 240-V motors. • Larger blowers will commonly use belt drives: • Adjusting pulley diameters will adjust fan speed. • Motors over 5 hp are usually three-phase 240-/460-V motors: • Rotation can be changed by reversing any two leads. The voltage most often supplied to the outdoor unit in a residential system is 240-V single-phase power. Air-handling equipment with capacities of 4,000 cfm or more typically utilizes belt-driven blowers with three-phase motors. Changing the speed of a belt-driven blower involves changing motor pulleys or adjusting the drive pulley diameter (if that feature is available). Motors above 5 hp that are used with belt-driven fans are typically 240-/460-V three-phase motors. Reversing the connections of any two motor leads can change the direction of rotation of a fan driven by a three-phase induction motor.

24. Grounding • It is important to maintain a proper ground connection to electrical equipment at all times: • Proper grounds reduce shock hazards; • Green or bare wire should be used; and • Older systems often used the metal conduit to provide a ground path. The frame of an electric motor is grounded to maintain the frame at zero electrical potential. When replacing a motor, you must ensure that the ground wire is reconnected for your protection and for the protection of anyone else coming in contact with the unit.

25. Overcurrent Protection • Fuses are designed to protect conductors, not motors: • A standard fuse may be rated up to 300% of the motor’s FLA. • Time delay fuses should be rated at 125% of the motor’s FLA. It is important for proper overcurrent protection to be used for all electric circuits. A line-voltage fuse is sized to protect the conductors or wires that supply power to the load. The National Electrical Code (NEC) specifies that motors must be protected with motor-duty fuses or circuit breakers that are sized at three times the motor’s full-load amperes (FLA). For example, a 60-A dual-element time-delay fuse should be selected for use with a 20-A motor. When you check the continuity of a fuse with an ohmmeter, always make sure that the power is turned off.

26. Motor Voltage • Actual voltage should not exceed ± 10% of the motor nameplate. • Motors rated at 208/230 V ac should not drop more than 5% below the 208 V (198 V). A motor may be operated with an impressed voltage that is +/-10% of the nameplate voltage. For example, the 120-V motor in the gas furnace used in a dual-fuel application may be operated with a voltage input as low as 108 V (120 – 12) or as high as 132 V (120 + 12). When a motor is operated with voltage that is lower than the prescribed limit, an increase in current draw will occur that may trip the overload. When voltage is measured across a motor and current is not measured, it is likely that the internal overload device is open. In the case of motors used in compressors that are rated for 208/230 V ac (which includes most equipment utilized in residential and light-commercial installations), the impressed voltage allowed by most manufacturers falls in the range of 198 V to 253 V. (The lower limit is –5% of 208 V, and the upper limit is +10% of 230 V.) When operated outside these voltage limits, a motor will run hot and trip on thermal overloads.

27. Switching • Low-voltage controls are most often used to provide switching for line voltage loads and provide safety for the technician. Benefits include: • Safer control voltage; • More accurate controls; and • Meeting of code requirements. The HVACR industry widely uses low-voltage devices to control the operation of loads that consume high voltages. This strategy provides many benefits. Perhaps most important of all, it offers safety for technicians working on the control circuits. Low-voltage sensing devices provide better control of temperature, because they are more responsive than high-voltage controls made of heavier material. In some regions of the country, an electrician must be licensed in order to work on high-voltage controls, whereas that requirement may not apply to technicians working on low-voltage controls.

28. Relays, Contactors, Starters • Relays, contactors and starters are very similar devices that energize a magnetic coil to open or close at set of switches: • Relays are 15 amps or less; • Contactors are 15 amps or more; and • A starter is a contactor with overload protection. • Number of poles. • NO or NC.

29. Relay Coil • Wire wrapped around an iron core. • Verify condition with an ohmmeter (power off). • Verify voltage to coil. • Voltage drop should not be present across closed contacts. The coil of a relay or contactor is a continuous length of fine wire wrapped around an iron core. Alternating current passing through a coil continually builds and collapses magnetic fields. These magnetic fields are enhanced by the iron core, and used to operate the switch or switches attached to the coil. You may determine whether the wire in the coil is intact by using an ohmmeter to read the resistance of a de-energized coil. An infinite resistance reading indicates that the coil is open. A resistance reading indicates that the wire in the coil is not open. When replacing a relay or contactor, you must choose a replacement that has the same coil voltage, switch configuration and contact ratings. If all three of these factors are not equal to the relay or contactor being replaced, the new component will fail to perform as it should. Damage to the relay may occur. Before condemning an existing relay, check to make sure that the correct voltage is being supplied to the coil. For example, to check the control voltage to a residential indoor blower relay, you should set the thermostat blower switch to the “ON” position and check for 24 V at the relay coil. If the correct voltage is supplied to the coil and it fails to operate, the relay must be replaced.

30. Current Relay • Smaller systems may make use of this component. • Contacts remain closed during inrush current. • Contacts are opened when motor reaches 75% of full running speed. Some smaller systems use a current relay rather than a potential relay in the starting circuit, as shown in the schematic on this slide. Unlike a potential relay, the contacts of a current relay are normally open and the wire in its coil is heavy enough to carry current supplied to the run winding of the motor. The inrush current is always greater than the holding current of a relay coil. A current relay responds to the higher inrush current that occurs when the motor starts and momentarily closes its contacts to engage the start capacitor. The starting current of a motor is typically five times its running current. As the motor reaches approximately 75% of its full running speed, the current draw of the circuit will drop and the current relay contacts will open, thus taking the start capacitor out of the circuit.

31. Electronic Control Boards • Electronic control boards provide switching based on multiple inputs. • Controls component timing. Newer systems include control boards that perform multiple functions. It is common for electronic control boards to be used for regulating the operation of a packaged air-conditioning system by bringing on the indoor blower, the compressor and the condenser fan all at the same time. An important reason for using electronic controls is that they can make decisions based on many inputs.

32. Sequencers • Sequencers provide staging of electric heating elements to reduce the high inrush current that would result from starting them all at once: • A specific purpose time delay relay. Just as motors must be controlled with switches, the electric heating elements used for auxiliary heat in a heat-pump system also must be controlled. In a system requiring a smaller electric furnace for supplemental heat, the heater may be controlled with a contactor that has contacts rated for the current draw of the heater. Larger electric furnaces have more stages of heater elements. These stages may be known as banks or racks of heaters. Switching all of them on at once would result in an inrush of current that would affect other appliances and lighting in the home. Sequencers are switching devices used in larger electric furnaces to bring on heating elements in stages, thereby avoiding an inrush of current that could dim lights in the home. A sequencer in an auxiliary electric heater energizes one or two heating elements and the blower motor simultaneously, followed by the remaining elements in timed intervals. Sequencers do not have magnetic coils that operate the switch contacts, as do relays and contactors. They are built with heaters or motors that close the contacts individually over a period of several seconds. In all applications, switches are power-passing devices and must not consume or steal power from the load being controlled. A voltage reading across a closed switch when the load is energized indicates that the switch is consuming power that was intended for the load.

33. Mild-weather Control • Fan-cycling control designed to reduce the evaporator load and in turn the head pressure during mild weather: • Prevents the heat pump from tripping out on high head pressure. Some heat pumps may experience an occasional cutout by the high-pressure control when operated in the heating mode during mild weather. Mild-weather controls are used in such cases to cycle the outdoor fan motor to reduce the amount of heat taken from the ambient air. This reduces the discharge pressure of the compressor. The mild-weather control is a normally closed (NC) pressure switch located on the vapor line between the indoor coil and the reversing valve. The contacts of the control are wired in series with one lead of the outdoor fan motor.

34. Capacitors • A capacitor is a device that has the ability to store an electrical charge. • The capacitor has two plates separated by dielectric material. • The capacitor creates a phase shift in the opposite direction as that created by a motor: • This correction can improve motor torque and efficiency. Capacitors are devices that store an electrical charge. They are used in HVACR systems to give a single-phase motor the extra starting torque it needs during start-up and to improve the running characteristics of the motor. The storage capacity of a capacitor is measured in microfarads (μF). Capacitors with larger capacitance ratings have more storage capacity. Each capacitor also has a voltage rating, which indicates the electrical pressure (or voltage) that the capacitor can withstand without breaking down. Capacitors are constructed of two parallel metal plates separated by an insulator known as a dielectric. The metal plates are usually made of aluminum. Typical dielectric materials include air, paper and aluminum oxide. The size of the plates, the dielectric material used and the thickness of the dielectric determine the storage capacity of a capacitor.

35. Capacitors • Microfarad rating – ability to hold a charge. • Voltage rating – maximum voltage the dielectric can withstand. • Capacitors can be tested with an ohmmeter : • Opens; • Shorts; and • Grounds. • Actual microfarad readings must be checked with a capacitance meter. • A failed capacitor will prevent a motor from starting or cause it to run hot. You will encounter two types of capacitors in your work as a technician, the start capacitor and the run capacitor.

36. Start Capacitor • Designed to stay in the circuit for a short period of time (until motor has reached 70% to 80% running speed). • 75mfd to 600 mfd. • No cooling required. • Primary function is to increase starting torque. As previously mentioned, a start capacitor is intended to be in the motor circuit for only a short time. It is used to provide extra torque to overcome inertia when the motor is starting. When the motor is reaches 70% to 80% of its full runningspeed, the start capacitor is no longer needed and is taken out of the motor circuit by a centrifugal switch, a potential relay or a current relay. The start capacitor should have a 15,000 Ω to 18,000 Ω - 2 W resistor soldered across the contacts. When the capacitor is removed from the circuit, the resistor will discharge the capacitor. This protects the contacts of the start relay. Start capacitors are commonly available in capacities ranging from 75 μF to 600 μF. They are considered “dry” because the plates and the dielectric are placed in the casing with no surrounding fluid for heat dissipation. Hard-start kits are often required with start capacitors for systems that use reciprocating compressors and TEV metering devices.

37. Run Capacitor • Designed to stay in the circuit during the entire run cycle. • Will require cooling: • Oil is used to dissipate the heat. • 2mfd to 60mfd. • Primary function is to improve efficiency. The run capacitor is designed to remain in the motor circuit after the motor is operating. It improves the motor’s running efficiency by improving the power factor. The power factor is a number (ranging from 0 to 1) used to relate input power to output power. For example, if the power used is 1,000 W and the work obtained also is 1,000 W, then the power factor of the motor is 1. But if the motor consumes 1,000 W of power and produces only 700 W of work, then its power factor is 0.7. Run capacitors are available in capacities ranging from 2 μF to approximately 60 μF. These capacitors are used on motors that are specially engineered to operate with the start winding in the circuit when the motor is energized. Because they are in the circuit continuously when the motor is energized, run capacitors produce heat that must be dissipated. Special oil is used to fill the metal case of the capacitor. The oil absorbs heat from the plates and transfers it to the metal shell and ultimately to the surrounding air. For this reason, a run capacitor is known as a “wet” capacitor.

38. Solenoid valve • Solenoid valves use a magnetic coil to open or close a valve: • NO or NC. • Reversing valves for heat pumps. • Pump down system.

39. Solenoid valve A solenoid is a coil of wire that generates a magnetic field when an electric current is passed through it. It may be either normally open or normally closed. A normally closed solenoid valve is in the closed position when the coil is de-energized and will open when the coil is energized. A normally open valve is in the open position until the coil is energized, at which point it will close. A solenoid valve operated with insufficient voltage or current will vibrate or chatter. Reverse-cycle operation is achieved in a heat-pump system by using a reversing valve (also called a switchover valve). The slider within the reversing valve is constructed with a piston at each end. Moving the slider and its pistons inside the valve body allows redirection of refrigerant vapor. This mechanism is used to direct high-pressure hot vapor to the outdoor coil during the cooling cycle while allowing suction vapor to be drawn from the indoor coil. During the heating cycle, it directs the hot vapor to the indoor coil while allowing suction vapor to be drawn from the outdoor coil. Refrigerant vapor pressure is used as the force needed to move the slider within the valve body. A solenoid is used on the pilot valve to direct the refrigerant vapor to the appropriate area of the main valve body and cause the slider to move. You may check the reversing valve solenoid coil by touching the nut holding the solenoid on the pilot valve with a screwdriver while the solenoid is energized. A good solenoid coil will produce sufficient magnetism to pull on the metal shaft of your screwdriver. Under no circumstances should you energize a solenoid coil when it is removed from the pilot valve. Doing so will damage the coil. During “OFF” periods, refrigerant tends to condense and pool in the evaporator (and possibly in the suction line). On the next call for cooling, this liquid refrigerant can slug the compressor, causing damage. Pumping the system down at the end of a cooling cycle sweeps refrigerant from the evaporator coil and suction tubing into the condenser or receiver. A low-pressure switch turns the compressor off before a vacuum is achieved on the low-pressure side of the system. This action prevents refrigerant from pooling in the low-pressure circuit during the “OFF” period. A solenoid valve also can be used to ensure that a solid column of liquid refrigerant enters the expansion device in systems where the compressor is located above the evaporator. In such an application, the valve is installed in the liquid line near the expansion device. At the end of the cooling cycle, the solenoid will close and the system will pump itself down. Liquid refrigerant will be trapped in the liquid line between the solenoid valve and the condenser. On the next “call” for cooling, the solenoid will open and a full column of liquid refrigerant will flow through the expansion device.

40. Transformer • Step up. • Step down. • Primary winding. • Secondary winding: • Voltage supplied to the primary induces a voltage into the secondary (no electrical connection). • Turns ratio. • Multi tap. • VA rating.

41. Transformer • Specific primary voltage. • Multi-tap secondary. • Rated in VA. • Should be fused. Each transformer is designed to be supplied with a specific primary voltage. The voltage supplied to the primary winding must be +/-10% of the rated or nameplate voltage. For example, a transformer with a primary voltage rating of 230 V may be operated with an input voltage as low as 207 V (230 – 23) or as high as 253 V (230 + 23). Damage to the device can occur if incorrect voltage is applied to the primary winding. When replacing a defective transformer, be sure to use an exact replacement whenever possible. If the exact replacement is not available, the specifications of the new transformer must match those of the old one.

42. Thermostat • Temperature controlled switch. • Needs to be installed away from: • Sunlight; • Supply grilles; and • Other heat sources. • Controls: • Compressors; • Fans; • Heaters; and • Reversing valves.

43. Thermostat Types • Bimetal. • Electronic. • Sensing bulb. • Low-voltage . • Line voltage. • Low ambient.

44. Bimetal Thermostats • Two dissimilar metals bonded together that will warp with a change in temperature. • Wrapped into a spiral to increase the length and amount of movement per degree of temperature change. • Magnet made be added to provide fast action of the contacts. • Mercury provides the same function: • Mercury stats must be mounted level; and • Mercury is a hazardous material.

45. Anticipators • Heat anticipators: • Connected in series with the heating control device; • Energized during a call for heat; and • Adjustable. • Cooling anticipators: • Connected in parallel with the cooling thermostat; • Energized during the off cycle; and • Non-adjustable.

46. Sensing Bulb • A gas-filled bulb. • Pressure increases or decreases with a change in temperature. • Pressure works against a bellows to open or close a switch. • Generally used in outdoor applications.

47. Electronic • Microprocessor based controls that use thermistors to sense temperature: • PTC or NTC. • Electronic thermostats often need a common connection to provide 24 V to operate. • Programmable: • 7 day; and • 5/2 day. • Intelligent recovery.

48. Line Voltage • Line-voltage thermostatsdirectly switch 115-V or 208-V/230-V loads. • Used almost exclusively on baseboard or zone electrical heaters

49. Low Ambient • Low-ambient controls are used to lock out equipment when the temperature drops below the setpoint. Low-ambient thermostats are used in some heat-pump systems to stop the compressor when the outdoor temperature drops to around 10°F (Factory default). To reduce wear on the compressor, some manufacturers choose not to operate compressors in their systems during periods of very low temperatures. Located in the outdoor section, this type of control is wired in series with the indoor thermostat and the compressor contactor holding coil.

50. Electrical Components North Seattle Community College HVAC Program Instructor – Mark T. Weber, M.Ed.