HVACR214 – Electrical for Oil

1. HVACR214 – Electrical for Oil Thermostats

2. Typical Oil Wiring Diagram

3. Control Systems • Remember there are 2 types of circuits. • Control Systems are series and control a load. • Loads are normally wired in parallel.

4. HVAC Controls • Heating systems have several levels of controls. There are the basics and then the more complex the system gets so do the controls. • The levels are split into: • Basic On/Off control • Safety Controls • Efficiency (comfort) Controls

5. Thermostats • The most basic control device for the heating system. • This is where it all starts – Customer turns it down, heat should come on. • In most) the thermostat is 24 volts.

6. Thermostats • The thermostat is the most frequently changing device in the HVAC industry. • But they all do the same thing – turn it on, and turn it off at the proper temperature. • Basic function of the thermostat is to respond to a change in temperature by opening or closing a set of contacts.

7. Thermostats • A thermostat is a switching device. • Thermostats can be line voltage, control voltage, or direct digital. • Line voltage are most often used in electric heat applications as well as refrigeration. • Control voltage thermostats are used mainly in residential or small office applications.

8. Thermostats • Direct Digital Controls (DDC) are most often used in large office, commercial or public buildings. If time allows at the end of this term we will talk more about DDC. • For the purpose of this term we will be discussing Control Voltage (low voltage thermostats).

9. Thermostats • There are now three types of sensing elements that are used in thermostats. • The controlling part of the thermostat is the part that moves or causes the contacts to close when the thermostat senses a change in temperature.

10. Thermostat Controlling Elements • Bi-metal: • Contain two pieces of dissimilar metals that are welded together. • These metals expand or contract at a different rate. • When heated or cooled they bend and move the contacts closer together or further apart.

11. Bi-Metal Elements

12. Thermostat Controlling Elements • Bi-metal: • This movement of the metal and the contacts can move a mercury bulb or bring a magnet on the contacts together. • The thermostat must have a way of making a good connection with the contacts. This is called “snap acting”.

13. Thermostat Controlling Elements • Remote Bulb: • Has a bulb filled with a liquid and/or gas. • The liquid and gas expand, travel down a capillary tube. • The expanded material puts pressure onto a diaphragm and this in turn closes or opens a set of contacts.

14. Thermostat Controlling Elements • Solid State: • Most digital or programmable thermostats use a solid state control. • Uses a material that changes resistance based on temperature. • Knowing the resistance the thermostat can judge (and display) the correct temperature. • Longer and more accurate life span, no moving parts.

15. Heat Anticipators • When a furnace is warming up after the thermostat calls for heat the temperature continues to drop. • The furnace holds a lot of heat and will continue to provide heat to the space as it cools down. This is called “over-shoot”. • To prevent this most thermostats contain a device called a Heat Anticipator

16. Heat Anticipators • Heat anticipators are small resistors built into the thermostats that generate some heat during a call for heat. • The bi-metal senses this additional heat and causes the thermostat to shut down a little before the room is satisfied.

17. Heat Anticipators • This allows the remaining heat in the furnace or water to be released into the room while preventing the room from over heating. • Solid state thermostats do not have adjustable anticipators. • Adjustable anticipators must be set to the amperage of the gas valve or heating relay.

18. Heating Anticipator

19. Heat Anticipator Problems • If the setting is to low: • Excess Anticipation (on cycles to short) • Rapid cycling • Small temperature swings, with a tendency to droop (stay below setting)

20. Heat Anticipator Problems • If the setting is to high: • Insufficient anticipation (on cycles to long) • Infrequent cycling • Wide temperature swings from setting with a tendency to lag.

21. Temperature Chart

22. Thermostat Safety • Know what voltage it controls • DO NOT TOUCH A BROKEN MERCURY THERMOSTAT. IT IS ENVIRONMENTAL WASTE AND CAN BURN YOU SEVERLY.

23. Thermostats • No matter what thermostat you have the basic principles and the wiring is the same.

24. Simple Single Stage Thermostat

25. Thermostat Wiring • R – 24volt to thermostat • W – Heating • Y – Cooling • G – Fan / Indoor Blower ------------------ OPTIONAL --------- • C – Common • O – Reversing Valve (More in Heat pumps) • Y2 – Second Stage Cooling • W2 – Second Stage Heating

26. Thermostat Wiring • Thermostats may have different wiring diagrams like the next slide but the functions are still the same. • What is the easiest way to find out what terminals on a thermostat do what functions?

27. 2 Heat / 2 Cool Thermostat

28. Control Connections

29. Electronic Thermostat Block