1. Thermostats

2. I would recommend that as you proceed through this power point presentation that you refer to your textbook, Unit 14, for some great visuals and additional information.

3. There used to be two major players when it came to the ID (identification code) used on thermostats. Those two players were: ITT (International Telephone and Telegraph) and Honeywell. You may still see some ‘old’ thermostats with the ITT ID code on them, but Honeywell’s ID code is what you will see today.

4. There may also be some manufacturer specific ID code as well. This presentation will briefly mention the ITT code, but will focus on Honeywell’s ID code.

5. Honeywell ID codeITT ID codeMeaning R W Y G V H C G or F Voltage/Power Heating Cooling G or Fan The terminals shown above are basic and there are more than these four. Additional terminal letters and their ID meaning can found via the internet and/or manufacturer’s literature.

6. The ‘R’ or ‘V’ ID is the terminal on the thermostat that is connected to the ‘P’ power side of the low voltage transformer. The color of the wire is unofficially ‘red.’

7. The ‘W’ or ‘H’ ID is the terminal on the thermostat that is connected to the heating equipment. The color of the wire is unofficially ‘white.’

8. The ‘Y’ or ‘C’ ID is the terminal on the thermostat that is connected to the cooling equipment. The color of the wire is unofficially ‘yellow.’

9. The ‘G’ or ‘F’ ID is the terminal on the thermostat that is connected to the fan relay which controls the fan speed for heating and cooling. The color of the wire is unofficially ‘green.’

10. Moving onto the application of thermostats.

11. HEATING ONLY thermostat This would be used where air conditioning would not be required. The heating only thermostat has a base and a mounting plate for installation.

12. Thermostat Equipment RR WW RED Wire WHITE Wire HEATING ONLY This circuit would require only two wires to function.

13. The ‘older’ electromechanical thermostats had an ‘anticipator.’ There is a good discussion of this in your textbook.

14. What is important for you to know about the electromechanical thermostat heating anticipator? 1.is wired in series 2.if it should fail open the heating equipment will not work 3.it is adjustable and needs to be adjusted based on the actual load current in the heating circuit. The amp. (current) value for the circuit is performed with an ammeter and a 10 loop coil. The 10 loop is wired in series with the W (heating) circuit.

15. The electronic thermostats do not use an anticipator like the older electromechanical thermostats. BUT they do need to be adjusted. This is not done with the 10 loop method, but one must check with the manufacturer of the thermostat and follow their directions.

16. COOLING ONLY thermostat This would be used where heating would not be required. The cooling only thermostat has a base and a subbase for installation.

17. The ‘older’ electromechanical thermostats had an ‘anticipator.’ There is a good discussion of this in your textbook.

18. What is important for you to know about the electromechanical thermostat cooling anticipator? 1.is wired in parallel with the thermostat contacts 2.if it should fail open the cooling equipment will continue to work 3.it is NOT adjustable 4.occupant would probably never know it is defective.

19. The electronic thermostats do not use an anticipator like the older electromechanical thermostats. BUT some of them may require adjustment. Check with the manufacturer of the thermostat and follow their directions.

20. Thermostat Equipment RR YY RED Wire BLUE Wire COOLING ONLY This circuit would require three wires to function. The unofficial color code for the wires could be what is shown, or different. Sometimes the RED wire is a BLACK wire. GG GREEN Wire

21. COOLING ONLY thermostat The cooling only thermostat would have a subbase with the following two switches on it. A system switch to set the thermostat for CLG – OFF and a fan switch with the functions: AUTO – ON.

22. COOLING ONLY thermostat The system switch has two positions designated to turn the air conditioner on (CLG.) or off (OFF).

23. COOLING ONLY thermostat The fan switch has two positions designated to turn the fan on (ON) or auto (AUTO). Please refer to your textbook for some visuals on this switch. The fan ON position will turn the fan on continuously for the speed required for cooling. The AUTO position will cycle the fan when the air conditioner is operating.

24. COOLING ONLY thermostat In both situations, this fan switch found on the thermostat will only operate the fan on the speed for air conditioning. So do not confuse this fan switch with the fan switch on a furnace that operates the fan on the speed for heating.

25. HEATING and COOLING thermostat The older electromechanical heating and cooling thermostats required a base and a subbase. The subbase is where the system and fan switch. The electronic thermostats are usually a one piece assembly and do not have a subbase. There are electronic touch screen programmable thermostats that do not have a subbase either. All functions of the thermostat are programmed at the time of installation.

26. Thermostat Equipment RR WW RED Wire YELLOW Wire HEATING and COOLING This circuit would require four wires to function. The unofficial color code for the wires could be what is shown. YY GREEN Wire GG WHITE Wire

27. Here is an example of an electronic thermostat with its cover removed to expose the terminals.

28. System Switch

29. Fan Switch

30. Terminal Identification

31. The next thermostat circuit is going to show an ‘isolated’ heating and cooling circuit. This means that there are two low voltage sources. One source would be for the heating system and the other source would be for the cooling system. The sources MUST not be put together, so they are ‘isolated’ at the thermostat.

32. Thermostat AC Equipment RHRH R R RCRC RED Wire YELLOW Wire This circuit would require five wires to function. The unofficial color code for the wires could be what is shown. YY GREEN Wire GG WHITE Wire Heating Equipment W W BLACK Wire

33. Did you notice that on the previous slide the thermostat had 2 ‘R’ terminals? One labeled R or RH RH for heating and the other one labeled RC RC for cooling. The thermostat may have both terminals with a ‘jumper’ connecting the two. If the ‘isolation’ is not required, the ‘jumper’ would be left alone. If the system requires ‘isolation,’ the jumper would have to be removed.

34. Terminal Identification R and RC RC with jumper installed from factory.

35. Examples of isolation: 1.Gas or Oil fired boiler with air conditioning. 2.Heating and cooling system with heating system using DC volts and air conditioner using AC volts.

36. There are heating systems with stages of heating and this is represented on the thermostat and equipment as: W 1 - first stage W 2 - second stage

37. There are cooling systems with stages of cooling and this is represented on the thermostat and equipment as: Y 1 - first stage Y 2 - second stage

38. A review of transformers: 1.Step down – output voltage lower than input 2.Step up – output voltage greater than input 3.Rating is: VA and Primary and Secondary E 4.Primary is connected to the line. 5.Secondary is connected to the load.

39. This concludes this review of thermostats.