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How to Set the Thermostat FAN AUTO ON or OFF Switch
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FAN ON OFF AUTO switch on thermostats, guide to setting, troubleshooting, repair: this article explains the use, setting, and adjustment of the FAN ON- AUTO button or switch or the FAN ON-MAN switch on room thermostats. This website answers most questions about central heating system thermostats & controls, troubleshooting, installation, inspection, diagnosis, and repair.
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Guide to Air Conditioning or Heating System Blower FAN ON-AUTO and FAN MAN-AUTO Settings on Wall Thermostats
How does the FAN switch work on a digital heating or cooling thermostat and how should I use the FAN switch? Details are just below.
FAN Button AUTO and ON functions on Digital Thermostats
 On most digital thermostats, pressing the "FAN" button repeatedly will cycle the fan control between two positions. Here we are using a Carrier™ digital thermostat for our examples. Our pencil points to the "FAN" switch or button in this case.
- FAN switch set to: "ON" will set the blower fan on your heating or air conditioning system run all the time, no matter what. See CONTINUOUS BLOWER FAN OPERATION for reasons people may want to run the fan continuously.
FAN switch set to: "AUTO" run let the fan be turned on or off automatically under control of the heater or air conditioner itself - when the thermostat asks for heat and the furnace warms up the fan will turn on. At the end of a heating cycle when the thermostat is satisfied, the fan will automatically turn off.
Fan operation in an air conditioning system or heat pump operating in cooling cycle works similarly
On a digital room thermostat when you press the "FAN" button, look closely at the thermostat's digital display - you should see the word AUTO (photo above left) or MAN (Photo above right) appear somewhere in the display to let you know which setting you have selected.
Typically in the AUTO mode in a heating cycle the fan won't actually turn on until the furnace has warmed-up and the fan will turn off shortly after the furnace turns off at the end of a heating cycle.
Running the fan "ON" all the time, which we like to do in lots of cases, distributes air and temperatures more evenly all the time in the home and produces less of a surge of heat or cool air when the heater or air conditioner actually turns on.
The air conditioning or heating wall-mounted thermostat may have a fan or blower control switch with (usually) two set positions "ON" and "AUTO" or sometimes "MAN" or "AUTO"
On these switches located usually on the top, side, or bottom of air conditioning or heating thermostats, the "ON" position is not what you might think. But it's simple, as you'll see.
On some room thermostats the FAN switch may show positions labeled MAN and AUTO instead of ON and AUTO.
On these thermostats "MAN" or "manual" is the same as "ON" in this situation. There are advantages of running an air conditioning or heating blower fan continuously, and "AUTO" is the same as "AUTO which we discussed just above.
Don't mix up the digital thermostat's display of the word AUTO regarding fan control with the display's use of the same word AUTO elsewhere in the thermostat's display window to describe the overall thermostat MODE setting which we discuss at SWITCH FUNCTIONS on a Room Thermostat.
How Should I Set the FAN ON-AUTO or FAN MAN-AUTO Switch on My Thermostat?
 "AUTO" on the fan switch on your thermostat is the normal switch position for the fan control. Setting the fan control to "AUTO" will allow the fan to turn on when the air conditioning system (or heating system) are ready to blow cool (or warm) air into the building, and to turn off automatically when cooling or heating are not needed.
"ON" or "MAN" on the fan switch: there are reasons to leave the fan in the ON position on a heating or cooling system, but we do not recommend that you do this without first asking for advice from your heating and service technician. SWITCH FUNCTIONS on a Room Thermostat - and also FAN ON AUTO Thermostat Switch discuss how to set the HVAC blower fan to continuous operation, and what to do if the blower fan won't turn on or won't turn off
If your heating system does not use a fan, for example if you have forced hot water baseboard or radiator heat, this switch can be left alone as it's not doing anything for your heating system.
Our photo (above left) shows the Fan Auto-On selector switch found on the Honeywell RTH2300/RTH 221 room thermostat.
Also see the Fan Limit Switch Control for another method to cause a blower fan to run continually.
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 If your air conditioner or heating system fan blower unit was designed to permit the fan to run all of the time that's great and you can consider the benefits of continuous fan operation which are described in detail in the articles we list just below.
Our photo (left) illustrates the FAN ON AUTO conrol switch (as well as the HEAT OFF COOL swtich) on a 3M Filtrete 7-Day programmable room thermostat. Watch out: the Filtrete™ 3M-22 is a battery-operated thermostat. If the batteries fail the thermostat may fail to provide heating or cooling and the building may suffer accordingly.
You might not want to keep the fan in "ON" mode if
Your furnace or air conditioner air handler is not designed for continuous fan duty - it might wear out the fan motor or bearings a bit early (ask your system's manufacturer or your HVAC tech about your system's capability)
Your building's heating system and return air duct design results in blowing uncomfortably cool air out of heating supply ducts when the furnace is not actually in heating mode.
See at CONTINUOUS BLOWER FAN OPERATION for details of continuous blower fan operation.
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What to do if the Blower Fan Runs Continuously and Won't Shut Off?
Some readers have written to say that their air conditioning blower was running continuously and they didn't know why.
If the blower or fan switch is set to MAN or ON, It could be that the FAN switch had simply been set to force the fan to run all of the time. Change the setting to AUTO and see what happens.
Other causes for an air conditioning blower fan that does not turn off could be a problem with the control circuit board for the air conditioning system, or there could be other operating system problems that are preventing the system from cooling air to the desired temperature.
If the blower or FAN switch is set to AUTO and the fan never turns off, call your air conditioning or heating repair company for diagnostic help, or if you've checked the switches we describe above and you want to diagnose the fan yourself, go to our blower fan diagnostic home page at FAN, AIR HANDLER BLOWER UNIT.
Frequently Asked Questions (FAQs)About the FAN switch on Thermostats
Questions & answers or comments about using and wiring the thermostat FAN AUTO, ON, OFF switch control for heating, heat pump, and air conditioning systems
Question: Where does the white wire go?
On a york roof mount heat and air system thermostat wire white go to the com terminal or the white terminal - Gary
Reply:
Not sure for your system which wire goes to which terminal - take a look at the wiring instructions on the appliance or in the installation manual to be sure. If you give me the product name and model number we can help find the installation and wiring instructions for a certain answer. I didn't find a customer service telephone number for York but the company's website includes consumer help and is found at http://www.york.com.
Also see THERMOSTAT WIRE CONNECTIONS where we give common and standard thermostat wire color coding and hookups.
Question: the A/C blower is not working properly in response to the thermostat
A friend's a/c unit has the blower fan that will only work in auto, it will not work on manual. On the other hand, even when you turn the unit from cool to off, the blower still remains on. The only way the blower will turn off, is to turn the fan to manual. He changed the thermostat, and the unit will cool to the desired temp and kick off, but you can't turn the fan off on your own unless you turn it to manual. Anyone ran into this before? - John
Reply: check thermostat wiring connections against the schematic for your unit and see these standard wire color codes
The wiring to the unit depends on if you have a heat pump, or straight a/c unit. It also depends on how the installer has wired the thermostat. With the heat pump, the red is power, the yellow is for cooling, the white is for heat, the green is for the fan, the orange is for the reversing valve, and the blue is usually always common.
Again, you will have to check to see how the installer has ran the wires from the thermostat. If you have a a/c only unit outside, you will only have a red wire, and a white wire coming form the inside unit, to the outside unit. These will go on the contactor to send 24 volts to the coil to pull the contactor in. These are the traditional wiring schematics, again, check the thermostat to see if this is the case with yours. - Bryan
Also see THERMOSTAT WIRE CONNECTIONS where we provide lists and tables of color codes and wire connections for thermostats in various uses.
Question: where does the white wire go?
on a york roof mount heat and air system thermostat wire white go to the com terminel or the white termanel - Gary 7/6/11
Reply:
Gary, please see THERMOSTAT WIRE CONNECTIONS
Question: proper control wiring depends on heat pump vs. A/C unit
A friend's a/c unit has the blower fan that will only work in auto, it will not work on manual. On the other hand, even when you turn the unit from cool to off, the blower still remains on. The only way the blower will turn off, is to turn the fan to manual. He changed the thermostat, and the unit will cool to the desired temp and kick off, but you can't turn the fan off on your own unless you turn it to manual. Anyone ran into this before? - John 8/17/11
Reply from reader Bryan:
The wiring to the unit depends on if you have a heat pump, or straight a/c unit. It also depends on how the installer has wired the thermostat. With the heat pump, the red is power, the yellow is for cooling, the white is for heat, the green is for the fan, the orange is for the reversing valve, and the blue is usually always common. Again, you will have to check to see how the installer has ran the wires from the thermostat. If you have a a/c only unit outside, you will only have a red wire, and a white wire coming form the inside unit, to the outside unit. These will go on the contactor to send 24 volts to the coil to pull the contactor in. These are the traditional wiring schematics, again, check the thermostat to see if this is the case with yours.
Bryan thanks for that succinct summary of usual thermostat wiring details and color codes. As it will help other readers I'll add it at "INSTALL & WIRE Thermostats" - if you want to be credited along with contact information let me know by using our website CONTACT link that displays our email addresses. Best, Dan. Also, readers with thermostat wiring questions should see THERMOSTAT WIRE CONNECTIONS - Ed.
Question: family dispute over how to operate a programmable thermostat
I am having a dispute with my family regarding the operation of our programmable thermostat. When the actual temp in the house is for example 20 degrees C., and the fan is turned to the ON position, the fan will start blowing 20 degree air. We all agree on that.
HOwever, when the option to use the TEMP UP button to raise the temperature is used, and the temperature is upped to 24 degrees for example(and the current temp is still at 20 degrees at the time that the TEMP UP is pressed), I maintain the IF the fan is again changed to the ON setting, the furnace will initially blow 20 degrees air which will increase gradually to 24 degrees as the furnace heats up. My family maintains that the furnace will immediately blow 24 degrees air (even though the current temp reading on the thermostat is 20 degrees). I believe that it will only blow the temp of air associated with the current temp. Can someone explain how it works? Thank you. - Betty 12/12/11
Reply: clarifying what the FAN ON does and the relation between thermostat control settings and temperature of air that's delivered
Let's try to clear up a few thermostat basics that may add fire to the family argument or may quench it a bit:
A thermostat is an -on-off switch, not an accelerator. More about this is at How Mercury Bulb Thermostat Switches Work & Why a Thermostat is Just an On-Off Switch.
But in sum, SETTING a temperature on the thermostat simply turns the heater or air conditioner ON. The heater or air conditioner will continue to run until the thermostat senses that the room temperature has reached the SET temperature, then the thermostat will turn that equipment OFF.
When you turn the fan to ON instead of AUTO, that tells the fan to run continuously. The temperature of air that the fan delivers will vary depending on whether or not the thermostat has ALSO turned the heater or air conditioner on or off - a separate function when you leave the fan always on. See FAN ON: Why Run an Air Conditioner or Heating Blower Fan Continuously? for details.
Questions or comments about this article
Questions & answers or comments about using and wiring the thermostat FAN AUTO, ON, OFF switch control for heating, heat pump, and air conditioning systems.
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Related Topics, found near the top of this page suggest articles closely related to this one.
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
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- [2] Thanks to reader S.R. for discussing loss of heat due to a thermostat wiring mistake, October 2010
- [3] Thank to Mr. Scott Meenen, G&S Mechanical Services, for providing some common thermostat wiring codes also found at Mr. Meenen's web page http://toad.net/~jsmeenen/wiring.html . Mr. Meenan provides heating, heat pump, and air conditioning repair services in Maryland, Washington D.C., and northern Virginia. He can be contacted at 301-591-1646 or by Email to jsmeenen@toad.net - 10/2010. Quoting:
We service American Standard, Amana, Arco, Arco-Air, Bryant, Carrier, Coleman Evcon, Comfortmaker, Day/Night/Payne, Dunham-Bush, Fedders, Fredrich, Goodman, General Electric, Heil, Intertherm, ICP, Janitrol, Lennox (Armstrong, Johnson Air-Ease), Miller, Modine, Nordyne, Rheem/Ruud/Weatherking, Sears, Stewart Warner, Trane, Weather King, Williams, White-Westinghouse, Whirlpool, Weil Mclain, York, (Frasier Johnson/Borg Warner) and others.
- [4] Azel Technologies Inc., P.O. Box 53138
10 Royal Orchard Blvd.
Thornhill, Ontario, Canada L3T 7R9
Ph: 905-223-5567 Fax: 905-223-3778
Email: info@azeltec.com, Website: www.azeltec.com.
- [5] Honeywell Controls, the company wants you to use their contact form at this web page: http://www51.honeywell.com/honeywell/contact-support/contact-us.html
Honeywell Consumer Products,
39 Old Ridgebury Road Danbury, CT 06810-5110 - (203) 830-7800
World Headquarters, Honeywell International Inc.,
101 Columbia Road,
Morristown, NJ 07962,
Phone: (973) 455-2000,
Fax: (973) 455-4807 1-800-328-5111
- Honeywell product model numbers & instruction Manuals: see http://yourhome.honeywell.com/home/Applications/FindYourModelNumber.aspx
- [6] White Rodgers Thermostats and HVAC controls,
Homeowner information: http://www.emersonclimate.com/en-US/brands/white_rodgers/Pages/wr-homeowner-info.aspx
Contractor information: http://www.emersonclimate.com/en-US/brands/white_rodgers/wr_contractor_info/Pages/white-rodgers-contractor-info.aspx
White Rodgers Product Catalog (don't misspell the company's name as White Rogers Thermostats) -
http://www.emersonclimate.com/Documents/thermostats.pdf - Thermostat Catalog
- [7] White Rodgers 1F90 Low Voltage Digital Comfort-Set thermostat Installation Instructions, PN 37-3654, White-Rodgers Division, Emerson Electric Co., 9797 Reavis Rd., St. Louis MO 63123
- [8] "Automatic Oil Burner Controls - Thermostats", Domestic and Commercial Oil Burners, 3rd Ed., Charles H. Burkhardt, McGraw Hill, 1969 (and later editions), ASIN B0000EG4Y8
- [9] Thermostat wiring color codes & conventions,
Thanks to reader "
Helpful Pointers" Regarding 24V T, 10/7/2012
- [10] Domestic Central Heating Wiring Systems and Controls, 2d Ed., Raymond Ward, Newnes, ISBN-10: 0750664363, ISBN-13: 978-0750664363, Quoting from Amazon.com:
This unique A-Z guide to central heating wiring systems provides a comprehensive reference manual for hundreds of items of heating and control equipment, making it an indispensable handbook for electricians and installers across the country. The book provides comprehensive coverage of wiring and technical specifications, and now includes increased coverage of combination boilers, recently developed control features and SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) boilers ratings, where known.
In addition to providing concise details of nearly 500 different boilers fuelled by electric, gas, oil and solid fuel, and over 400 programmers and time switches, this invaluable resource also features numerous easy-to-understand wiring diagrams with notes on all definitive systems. Brief component descriptions are provided, along with updated contact and website details for most major manufacturers.
- [11] Proliphix Corporate Headquarters,
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Phone: +1.978.692.3375
Toll Free (U.S.): 866-IP-LIVING (866.475.4846)
Fax: +1.978.692.3378 - Email: sales@proliphix.com or Customer support: support@proliphix.com Website: http://www.proliphix.com/ - quoting from the company's website:
All Proliphix Network Thermostats come with our free Uniphy Remote Management Service. This unique offering lets you monitor and control your HVAC systems by simply pointing your Browser to our secure Proliphix Web Site. Enjoy the convenience of programming a thermostat from any location, using a simple graphical interface. No computer equipment or software is required. And since Proliphix takes care of the network configuration for you, you’ll be up and running in no time. We’ll even proactively monitor your thermostats and send you an immediate email or SMS message when an HVAC problem is detected.
- Thanks to reader Harvey Tyler for suggesting clarification about how the heating or cooling thermostat FAN ON OFF switch actually functions on a digital thermostat. 02/03/2009
- Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
- Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
- National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
- The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
- Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
- The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
- Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
- "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
- "Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
- "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
- Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
- Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
- Installation Guide for Residential Hydronic Heating Systems
- Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
- The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
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