1 hvacr317 – core for refrigeration operating controls 1 thermostats operating controls 1...
TRANSCRIPT
![Page 1: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/1.jpg)
1
HVACR317 – Core for Refrigeration
Operating Controls 1Thermostats
![Page 2: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/2.jpg)
2
Thermostats
• The most basic control device for the Air Conditioning system.
• This is where it all starts – Customer turns it down, A/C should come on.
• In most split systems (Split system is where there is an air handler inside and a condenser outside connected by refrigerant piping) the thermostat is 24 volts.
![Page 3: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/3.jpg)
3
STATS ARE 2-STATE DEVICES
TEMPERATURE PRESSURE
HEATING CLOSES ON TEMPERATURE FALL
COOLING CLOSES ON TEMPERATURE RISE
HIGH PRESSURE SWITCH OPENS ON PRESSURE RISE
LOW PRESSURE SWITCH OPENS ON PRESSURE FALL
![Page 4: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/4.jpg)
4
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.
![Page 5: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/5.jpg)
5
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.
![Page 6: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/6.jpg)
6
VARIOUS THERMOSTATS
![Page 7: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/7.jpg)
7
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 AC 422 term we will be discussing Control Voltage (low voltage thermostats).
![Page 8: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/8.jpg)
8
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.
![Page 9: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/9.jpg)
9
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.
![Page 10: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/10.jpg)
10
Bi-Metal Elements
![Page 11: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/11.jpg)
11
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 (see figure 12.10 in your electrical book).
– The thermostat must have a way of making a good connection with the contacts. This is called “snap acting”. (see figure 12.8 in your electrical book).
![Page 12: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/12.jpg)
12
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.
![Page 13: 1 HVACR317 – Core for Refrigeration Operating Controls 1 Thermostats Operating Controls 1 Thermostats](https://reader036.vdocuments.mx/reader036/viewer/2022062422/56649f265503460f94c3d5b8/html5/thumbnails/13.jpg)
13
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.