Fan Relay Wiring Diagram

Above: Wiring diagram for the White Rodgers Fan Limit Control used at line voltage. [Click to enlarge any image] tailored from the White Rodgers 5D51 installation instructions cited here. Below: Wiring diagram for the White Rodgers Fan Limit Control used with low voltage equipment. Note that the jumper is remoed for use with low voltageWiring Diagram Images Detail: Name: air handler fan relay wiring diagram - Wiring Basic Free Download Diagrams Lively Household 11; File Type: JPGDescription: Alternating Relay Wiring Diagram Hvac Hvac Alternating Relay with Hvac Fan Relay Wiring Diagram, symbol measurement six hundred X 377 px, and to view symbol main points please click on the image.. Here is a picture gallery about hvac fan relay wiring diagram complete with the outline of the picture, please in finding the image you wish to have.Imperial Electric Fan Wiring Diagram Fan heart wiring diagram for furnace schematic 94a fan heart wiring diagram library lend a hand my ecobe3 out perform 20 t stat hvac diy chatroom honeywell fan center wiring diagram schematic. Whats other people search for on this weblog: How To Wire A Fan Center RelayRadiator Fan Wiring - Wiring Diagram Data - Cooling Fan Relay Wiring Diagram Wiring Diagram contains several detailed illustrations that show the relationship of varied pieces. It contains directions and diagrams for various sorts of wiring methods along with different pieces like lights, home windows, etc.

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How to Install & Wire the Fan & Limit Controls on Furnaces Honeywell L4064B & All White Rodgers Fan Limit Controllers

InspectAPedia tolerates no conflicts of interest. We don't have any relationship with advertisers, products, or products and services discussed at this website online.

Fan limit transfer wiring main points:

This article describes in detail the installation & wiring of furnace mixture controls, also often called the "fan limit switch" on warm air heating programs.

The photograph at the best of this web page displays all of the controls and wiring terminals in a Honeywell combination fan and restrict keep watch over installed horizontally on a gas furnace.

We also provide an ARTICLE INDEX for this matter, or you'll take a look at the page top or bottom SEARCH BOX as a quick technique to in finding data you want.

Advice for Installing and Wiring the Furnace Combination Control Fan Limit Switch on Heating Systems

Here we include each previous and current guides to Installing & Wiring Fan Limit Switches on Warm Air Furnace Heating Systems for all main manufacturers of fan restrict keep watch over switches used on heating furnaces and different fan programs.

In this newsletter collection we additionally talk about the following:

Furnace Combination Control Operating Temperature Range & Limits; Where to mount the furnace Fan-Limit Control; Honeywell Combination Furnace Control kind L4064 wiring hookup defined and illustrated in detail; Wiring Notes for the Combination Furnace Control L4064B; Honeywell L4064B Limit Wiring When Controlling Low Voltage - Control wiring Details

The comic strip at above/left, courtesy of Carson Dunlop Associates, shows an flawed (too excessive) upper restrict setting - this is an unsafe fan-limit switch setup which is prone to allow the furnace to overheat, risking warmth exchanger harm and dangerous carbon monoxide leaks. [Click to magnify any symbol]

Article Contents

The following instance of wiring a fan restrict regulate transfer is based on recommendation from the Honeywell Tradeline L4064B. Check the check specs supplied by the manufacturer of your particular keep watch over.

Furnace Combination Control Operating Temperature Range & Limits

The switch portion of this Honeywell Fan Limit control can tolerate 190 °F. and the sensing element can maintain as much as 350 °F.

The keep watch over can deal with 120V and 240V devices and can also be stressed out to keep watch over low-voltage units. The electric wiring used will have to also be rated for appropriate temperature exposure (Honeywell advises wiring rated for 167°F).

At 120V the keep watch over can switch fan motor lots at 14 Amps complete load (84 Amps locked rotor load), and the restrict switch (possibly an oil or fuel burner) can take care of up to 8 Amps complete load (48 Amps locked rotor load).

When controlling 240V devices the fan or blower keep watch over can handle up to 7 Amps full load (42 Amps LRA) and the restrict switch can maintain 4 Amps full load (24A LRA).

Where to mount the furnace Fan-Limit Control

This furnace aggregate keep an eye on is fastened at the furnace in a location where the bimetallic spring/probe (proven above on this article) will protrude into the nice and cozy air plenum to sense furnace air temperatures there. Each furnace producer will supply directions of the place, on their gadget, the air temperature will have to be monitored for regulate purposes.

The reason why the keep an eye on manufacturer warns that the keep watch over tip must now not contact any inside surfaces of the furnace is that doing so could cause mistaken reading of furnace air temperatures or could harm the regulate or prevent loose movement of the bimetallic spring in accordance with temperature changes.

Of route if you're changing an previous keep an eye on that has failed, just mount the control in the same location that held the prior unit.

When replacing an old furnace restrict regulate, ensure that the new control has a sensing tip of the same length because the unit being replaced. Otherwise the new regulate would possibly not paintings safely.

The producer provides details for floor mounting, rigid-bracket mounting, or swivel-mounting of the keep an eye on. Which of those methods you select depends on what mounting is had to position the sensor probe in the correct location within the air plenum.

Wiring the Furnace Combination Fan & Limit Control the usage of the Honeywell L4064B as an Example

This control may also be stressed out to serve as a security LIMIT switch on a furnace by wiring simply the limit terminals on the control. When the instrument is used both to keep watch over a furnace fan on-and off in addition to serve as a LIMIT switch, then all 4 terminals are used.

Fan control wiring: As Honeywell's representation displays, the 2 fan terminals are at the higher and decrease left aspect of the control.

Line voltage is stressed out at the backside left push-in terminal.

Load voltage (to the fan) is wired on the higher left push-in terminal.

Limit keep an eye on wiring: As the representation presentations, the 2 LIMIT terminals are at the upper and decrease appropriate aspect of the L4064B regulate.

The Line (energy in) cord is attached to the lower appropriate push-in terminal, and the Load (cord to grease or fuel burner) is wired to the higher correct push-in terminal.

The wiring diagrams proven in additional detail underneath are standard for wiring the furnace combination keep an eye on on heating techniques.

Remember that every one electric wiring of furnace controls (or any other electric units) must agree to nationwide and native electrical codes in addition to the specs of the control producer and the furnace producer.

Wires are connected to the control the use of push-in terminals. A wire strip gauge is equipped at the left facet of many versions of this keep watch over.

The regulate used for our footage got here with further push-in terminals (Part # 137813) that can be used to transform the push-in wiring connectors to screw-terminal connectors.

This is a brilliant idea if you are expecting to be converting wiring from time to time. (Dr. Jess Aronstein's research has demonstrated that repeated-use or re-use of push-in type terminals on electric receptacles does no longer supply an overly reliable connection. This is also true for this control as neatly.)

Fan Limit Switch Installation Manuals 1970 to Present, for Camstat, Cemco, Goodman, Honeywell & White Rodgers

Camstat Fan Limit Control Wiring

Cam-stat FAL7C-05TD-120-A Fan & LImit regulate (shown above) [Click to magnify any image]

Cam-Stat is a department of Supco. The Cam-Stat fan limit transfer provides a dial-adjustable FAN OFF temperature ranging from 90°F to 120°F, a FAN LIMIT temperature ranging from 150°F to 250F, and typically a hard and fast differential of 30°F. [Click to magnify any image]

Firestat Controller

Shown above: the Senasys Firestat HVAC duct fan limit controller, a fireplace protection software that turns off the HVAC blower in match of a hearth.

SUPCO Limit Controller Wiring Guides & Manuals CEMCO Limit Control Wiring Guides & Manuals CEMCO SENASYS TC-Series FIRESTAT DUCT FAN LIMIT CONTROL WIRING DIAGRAM, [PDF] Columbus Electric, SenaSys, 704 Bartlett Avenue Altoona, WI 54720, USA Tel: 715-831-6353 Email: [email protected] retrieved 2018/03/05, unique supply: [proven below]

Website Excerpts:The Columbus Electric TC Series FIRESTAT is a push-button manual reset restrict control designed expressly for fire prevention in heat air ducts.

It may be used with gasoline, oil, or electric pressured heat air heating methods. One or more FIRESTATS should be installed in duct work at critical temperature places comparable to down-stream from electrical warmers, points where duct paintings is in close proximity to flammable fabrics, etc.

FIRESTATS may be utilized in low voltage or line voltage circuits and are normally wired to open [the] circuit to each heat source and blower when duct air temperature exceeds the temperature setting [of the FIRESTAT safety instrument].

If a couple of FIRESTAT is attached to keep watch over a single warmth supply, the FIRESTATS must be connected in collection. A regular [FIRESTAT] wiring diagram is proven beneath [edited for clarity by means of].

[Click to magnify any symbol]

CEMCO SENASYS FIRESTAT DUCT FAN LIMIT CONTROL SPECIFICATIONS [PDF] retrieved 2018/03/05, authentic supply: Excerpts:

The TC Duct Limit Controls comprise a Helix Bi-Metal that senses speedy will increase in duct temperature reminiscent of hearth. The Bi-Metal reasons the in most cases closed contacts to open and flip off the facility

Available in both adjustable [TC-100, TC-105, TC-108] or mounted temperature [TC-205] models. These firestat restrict switches are put in in air ducts to close down heating, air con and ventilation apparatus when air temperature in duct exceeds a pre-set restrict.

The Duct High Temperature Limits characteristic a helix bimetal element that senses rapid will increase in duct temperature, reminiscent of the ones led to by way of fireplace. The high temperature limit then operates an SPST switch that opens with a upward push in temperature.

A guide reset button reactivates the temperature limit after the high-temperature situation has cleared. These duct excessive temperature limits are indispensable in specialized HVAC programs and Building Automation Systems.


Columbus Electric, initially in Columbus Ohio, U.S. is a department of TPI Corporation. The company produced HVAC controls including fan restrict controls such because the unit proven right here, line voltage electric warmth wall thermostats, and different controls and equipment.

Contact: Columbus Electric Division of TPI, PO Box 4973, Johnson City, TN 37602 USA, Tel 800-251-7828, Fax 423-477-0545orTPI Corporation, Website:, Tell: 1-800-682-3398. The corporate's current product traces include Markel Products, Raywall, and Fostoria and an excessively huge range of HVAC equipment and controls.

Columbus Temperature Control, Columbus Temperature Control, 1053 East 5th Avenue Columbus OH 43201 USA Tel: 614-294-6216 markets under Distech Controls and these days specializes in networked, digital interfaces and controls for security, HVAC, lighting, access control, energy menagement methods.

Thanks to reader Larry C. for the Columbus Electric Combination Temperature Controller photographs, 2018/07/25. He wrote that this control was once used on a dual-zone heating and air con gadget.

See LINE VOLTAGE THERMOSTATS for set up guides for other thermostats produced via Colubus Electric / TPI.

Goodman Furnace Controls

Honeywell Fan Limit Control Wiring & Manuals

HONEYWELL L4064B, L4064R UNIVERSAL COMBINATION FAN & LIMIT CONTROLLER INSTALLATION MANUAL [PDF] (2017) 69-00115-11 Honeywell 1985 Douglas Drive North Golden Valley, MN 55422-3992

This L4064B, L4064R limit controller is a common substitute for older furnace fan restrict controllers. Here is the variation between the L4064B and L4064R, excerpting from the file above:

These combination heat air fan and limit controllers are appropriate for more than a few varieties of compelled air heating methods. The controllers have 2 switches; one which opens the limit circuit if the plenum temperature exceeds the preset protection restrict; it resets robotically. The different transfer turns the fan off and on.

The fan is grew to become off and on consistent with plenum temperature.

The L4064R has a special excessive temperature range suitable for gravity heating programs.

All fashions would possibly be used as limit controllers via wiring most effective the limit aspect. Limit contacts are appropriate for both line voltage and coffee voltage. For low voltage programs, the brass jumper will have to be removed....Follow furnace or burner manufacturer’s directions, if out there.

Maximum component temperature is:

L4064B—350 ºF (177 ºC).

L4064R—250 ºF (121 ºC) above restrict setting.

Maximum transfer temperature is: L4064B,R—One hundred ninety ºF (88 ºC).

HONEYWELL L4064B-L4064R Fan Limit Control INSTALLATION INSTRUCTIONS-2013 [PDF] (2013) Form No. 69-0115-08 HONEYWELL SUPER TRADELINE L4064B UNIVERSAL FAN & LIMIT CONTROLLER INSTALLATION MANUAL [PDF] (2006) 69-0117-Three OBSOLETE but useful in case you have a keep watch over from this era; Product Data, installation & surroundings directions, retrieved 2017/04/23, unique supply: HONEYWELL TRADELINE L4064B, W COMBINATION FAN & LIMIT CONTROLER INSTALLATION MANUAL [PDF] (1984) Rev. 12-84, Form NO. 69-0116-2 OBSOLETE but helpful in case you have this older keep an eye on HONEYWELL L4064A-F, J,R,T,W,Y FAN LIMIT CONTROLLER INSTALLATION - ALL MODELS [PDF] (1985) Rev. 1-85, Form No. 68-0024-1 OBSOLETE however useful in case you have this older regulate

L4064 A-F, J, R flip the blower fan on/off in line with plenum temperature

L4064 T, W, Y have a 20-Ninety 2d lengthen prior to turning the fan ON after a thermostat name for heat (keeping off blowing cool air on occupants)

L4064 B,D,F,R,W have additionally a handbook FAN-ON transfer to stay the an on steadily

L4064 J,R had a distinct high-temperature range for older furnaces burning gasoline, oil, coal, picket

The keep watch over was once also sold as a SUPER TRADLINE mannequin that included a lot of mounting adapters and protecting covers.

HONEYWELL L4064A-F,J,R,T FAN & LIMIT CONTROLLER INSTALLATION & WIRING [PDF] (1981) Rev. 4-81 Form No. 60-2258-2 special due to reader Haydn Chambers for offering this record, 2018/03/04 HONEYWELL L4064T (ca 1970) wiring diagram shown below thanks to reader Haydn Chambers, used an additional set of spade terminals within the heart of the regulate - these were hooked up to low-voltage terminals that provided a fan-timer heater function comparable to shown within the illustration that features a low-voltage (24VAC) gas valve and thermostat.

Above: Honeywell L4046T Wiring diagram.

[Click to enlarge any symbol]

Below: Honeywell L4068A-C-E-F Wiring Diagrams from the manual given just below.

Honeywell L4064B Limit Wiring When Controlling Line Voltage (120V or 240V) - Control Installation Notes

In most packages within the U.S. and Canada the Honeywell L4064B mixture control is used to change off and on 115V-120V or 240V lovers and heating burners, or on some gas apparatus, the burner controls (the LIMIT switch serve as) operates at low voltage.

The pull-out or break-off tab mentioned beneath at HONEYWELL L4064B LIMIT WIRING WHEN CONTROLLING LOW VOLTAGE is left in position for line voltage applications.

[Click to enlarge any image]

The left-illustration shows normal wiring for this set-up. The fan or furnace blower motor is controlled via the 2 left connections (green dots); the furnace limit switch which is able to turnoff the burner if the temperature restrict is reached is controlled by way of the two appropriate connections (red dots).

Here the furnace limit transfer is controlling a line-voltage device. The coloured triangles refer to notes given below.

The illustration under displays the wiring for controlling line voltage when the jumper or pull out tab has been got rid of.

You can see that in effect the installer in impact is replacing the lacking jumper via installing a connection to each terminals on all sides of the contacts where the jumper was removed.

This essential detail allows this keep an eye on to be used to control line voltage (120V) units despite the fact that the jumper has been got rid of or the paper pull-out tab on older controls has been misplaced.

Wiring Notes for the Combination Furnace Control L4064B: Be sure so as to add a power disconnect switch and overload (fuse or circuit breaker) coverage on this circuit. Note that the jumper or paper tab has been left in position. Wires to regulate low-voltage equipment - in this case the jumper has been removed.

Additional set up details for this control in the most recent shape are out there from Honeywell (cited underneath).


Honeywell L4064B Limit Wiring When Controlling Low Voltage - Control wiring Details

Pull the tab at the bottom of the Limit Control to be used with low voltage apparatus

To get ready the L4064B furnace regulate to be used in a low-voltage application (usually 24VAC), simply remove the small pink cardboard tab shown at left or ruin off the copper jumper between the two contacts in the same location on more recent fashions of this keep watch over.

The brass jumper is the breakaway type. It will have to be got rid of when the limit is used in the low voltage circuit.

To take away jumper, damage with a needlenose pliers and take away utterly. Once removed, it's not replaceable.

If you are making a mistake and remove this tab and then notice that you want to use this keep watch over to maintain line voltage (120V or 240V) you can simply set up a jumper wire as we display within the right-hand illustration simply above on this page.

Reader Question: I forgot to remove the brass jumper on a brand new fan limit switch set up

I installed a new fan limit transfer but in my rush I overlooked casting off the brass jumper for low voltage.

I examined it and it began and stopped. I can't seem to in finding the damage.

Do i want to buy and replace the restrict transfer once more? I've checked the fuses and replaced both but nonetheless wont work. what else do I wish to verify. thanks


Dennis, I'm sorry to need to play it secure, however studying Honeywell's caution that the regulate might be broken, I simply would not take a likelihood.

Watch out: A problem is that simply as a dishonest spring can alternate how a switch plays, interior harm might be refined and no longer visible, however the fan limit may not carry out safely.

Certainly you'll cross during the recommended fan limit switch check procedures described above on this page to confirm that the swtich is doing what it is supposed to do.

If you might be still concerned I'd repalce the switch reasonably than take a possibility or lose sleep over it.

How to Wire the Honeywell L4064B to Control Low Voltage Equipment

The diagram at left presentations the way to twine the Honeywell L4064B mixture furnace control when it's used to control low-voltage apparatus.

This tab is located sticking out from the keep an eye on close to the center of the ground of its face. You'll see embossed at the keep watch over above this tab the phrases "Remove for Low Voltage".

Newer variations of this keep watch over have a brass jumper in the similar location. The brass jumper is damaged off for low-voltage use and isn't replaceable as soon as it has been removed.

The fan or furnace blower motor is controlled through the 2 left connections (inexperienced dots).

The furnace restrict switch which can turnoff the burner if the temperature restrict is reached is managed via the two correct connections (red dots). Here the furnace limit transfer is controlling a low-voltage tool comparable to a heating furnace gas valve. The colored triangles confer with notes given below.


Be certain to add a power disconnect switch and overload (fuse or circuit breaker) protectionOn this circuit. Note that the jumper or paper tab has been left in place. Wires to keep watch over low-voltage apparatus - in this case the jumper has been got rid of.

Before wiring this or any keep an eye on remember to obtain the most recent information from the manufacturer of the control and the furnace on which it's to be installed. Additional installation main points for the Honeywell L4064B Combination Fan Limit regulate in the newest form are available from Honeywell.

After wiring this keep an eye on remember to've use the proper settings by way of reading over FAN LIMIT CONTROL SETTINGS and then you'll want to take a look at the combo fan and limit transfer for safe and proper operation.

How to Check that the Fan Limit Switch is Working Properly

Excerpting from the 2017 document given under:

When set up is complete, disconnect the fan motor circuit at the L4064.

Turn on energy and set thermostat to name for warmth.

Burner should come on and limit controller will have to close burner off when plenum temperature reaches the limit set point.

Turn off power, reconnect the fan switch, turn on power and again set thermostat to name for heat.

The fan must get started when plenum temperature has reached fan-on environment. 

Honeywell L4068 & 4069 Fan & Furnace Controller Wiring

HONEYWELL L4068A,C,E,F & L6068A,D FAN CONTROLS [PDF] (1976) installation and wiring manual. The Honeywell L4068A,C,E,Ffan controls operate the furnace fan motor in line with plenum temperature in forced air heating systems. L4068G attic fan control operates an attic ventilation fan in response to attic air temperature. The L6068 air transfer is utilized in downflow furnaces to forestall opposite air flow and to offer coverage against excessive temperatures led to by means of vlogged filters. The L6068 may also be used to control a 2- Speed fan.

Wiring the White Rodgers 5D-series Fan Limit Controller

WHITE RODGERS DISC THERMOSTATS [PDF] product specifications, limit controls, fan controls, disc thermostats WHITE RODGERS 3L09 SERIES BOARD MOUNT LIMIT CONTROLS [PDF] 1/2" bimetal disc models & options WHITE RODGERS 5D51 UNIVERSAL FAN & LIMIT CONTROL [PDF] ] retrieved 2018/02/08 authentic source: WHITE RODGERS 50A55-842 SYSTEM CONTROL WIRING [PDF]

The 50A55-843 is an automatic gasoline interrupted ignition keep an eye on that employs a microprocessor to continually observe, analyze, and regulate the correct operation of the gas burner, inducer, and fan.

Signals interpreted all the way through power surveillance of the thermostat and flame sensing part initiate computerized ignition of the burner, sensing of the flame, and shut-off throughout customary operation.

WHITE RODGERS 757-1 / 758-1 FAN CONTROL & LIMIT CONTROL [PDF] retrieved 2018/03/04 original supply WHITE RODGERS UNIVERSAL FAN LIMIT CONTROLLER SPECIFICATIONS [PDF] offers full list of fashions and contours WHITE RODGERS 21M51U-843 UNIVERSAL INTEGRATED HSI FURNACE CONTROL KIT [PDF] wiring diagrams, for two-stage, integrated 3-speed (PSC) furnace controller, White Rodgers Corp., Replaces White-Rodgers 50M51-242 and 50M61-XXX's Two-Stage HSI Systems with 80V or 120V Ignitors

Includes a diagnostic table de-coding the fairway, amber, and crimson LED flash codes used in troubleshooting the furnace.

WHITE-RODGERS-FAN-LIMIT-CONTROL-5D51-35-78-90-INSTALLATION [PDF] White-Rodgers Division Emerson Electric Co. 9797 Reavis Rd., St. Louis, Mo. 63123-5398 (314) 577-1300, Fax (314) 577-1517 9999 Hwy. 48, Markham, Ont. L3P 3J3 (905) 475-4653, Fax (905) 475-4625 retrived 2018/03/04, unique source: in English and French.Excerpts:This fan and restrict keep an eye on combines, in one enclosure, a fan switch with an adjustable differential which operates the blower in a pressured warm air furnace and a limit switch with a fixed differential which robotically shuts off the burner if the furnace temperature exceeds a predetermined excessive point. A summer time fan switch is included in this control to supply a handy approach for handbook operation of the fan for air circulate all over the summer time.Cette commande de ventilateur et de limite mix, dans un seul boîtier, un interrupteur de ventilateur avec une différence réglable qui fait fonctionner le ventilateur dans un système à air pulsé et un interrupteur de limite à différence fixe pour arrêter l. a. chaudière si sa température dépasse une température élevée spécifiée.Un interrupteur de ventilation pour l’été est incorporé dans cette commande pour fournir une méthode pratique d’utilisation manuelle du ventilateur pour faire circuler l’air en été.

Watch out: To prevent electric surprise and/or apparatus damage, disconnect electrical power to machine at major fuse or circuit breaker field till installation is complete. Label all wires prior to disconnection when servicing controls. Wiring mistakes can cause mistaken and dangerous operation.

Following set up or substitute, practice equipment manufacturers’ really useful set up/provider directions to insure correct operation.

Do not use on circuits exceeding specified voltages. Higher voltages will injury control and may cause surprise or fireplace danger. If in doubt about whether or not your wiring is millivolt, low or line voltage, have it inspected by way of a qualified heating and air conditioning contractor or a approved electrician.

Above: Wiring diagram for the White Rodgers Fan Limit Control used at line voltage. [Click to enlarge any symbol] adapted from the White Rodgers 5D51 installation instructions cited right here.

Below: Wiring diagram for the White Rodgers Fan Limit Control used with low voltage apparatus. Note that the jumper is remoed for use with low voltage equipment, additionally tailored from the White Rodgers 5D51 installation instructions cited right here.

Other Limit Controls, Wiring & General Information

Warning on Wiring Limit Controls and Switches in Reverse Polarity Question: is it ok to cord the restrict transfer backwards with wires reversed in polarity from the instructions?

2018/10/01 John Ford stated:

Line voltage is stressed out on the backside left push-in terminal.

Load voltage (to the fan) is stressed at the upper left push-in terminal.

What happens if these are reversed & will it damage the restrict keep an eye on transfer

Reply: do not wire switches in reverse polarity: injury chance

Thanks for a crucial question, John as we've all pushed a wire into the wrong connector every now and then.

Watch out: Warning about wiring fan restrict switches or other controls in reversed polarity:

I don't know what specific fan restrict switch you're the usage of opposite wiring effects and I believe that the danger of wear and tear from wiring in reverse polarity is producer and model-dependent as well as dependent on an additional element I'll notice. Here are some normal remarks:

Most switches will "work" 'when stressed out in opposite polarity or "backwards" in that they turn-on or off the switched instrument as needed.

However wiring in opposite polarity can damage electric elements and may also be unsafe.

A overview of THE BASICS of LIMIT SWITCHES [PDF] an excellent file on restrict switches by Eaton, cited in detail beneath, reminds us that mis-wiring a switch as you requested may cause arcing when the transfer operates; that arcing in flip can injury the transfer or gadgets hooked up to it.


Limit Control Wiring Polarity Observations

Polarity is a time period which is used to explain the connection between the weight and line connections in a multicircuit switch.

Take a collection of contacts with terminals which are made electrically commonplace. If a line to line short circuit does no longer occur, those contacts are said to be connected to the similar polarity.

If a line to line short circuit does occur the contacts are mentioned to be of reverse polarity.

Some restrict switches have their units of contacts isolated from each and every different on the same pole. They are stated to have electrically remoted outputs and are classified as such.

Most gadgets, alternatively, wouldn't have isolated units of contacts on the same pole and care must be taken to look at polarity.

Failure to do so may cause permanent damage to the transfer, the wiring or each.

Additional remarks:

In some digital units leaving a reside connection to the aspect of a circuit that's normally no longer energized can every so often motive injury to a circuit or circuit board - a classic instance is the effect of stray currents at the impartial twine in a circuit that injury an appliance or travel an AFCI.

When wired improperly the heating gadget may be unsafe. For example as you'll be able to see within the Honeywell schematic I come with under, in the event you opposite line and cargo wiring you're preserving the motor and other portions of the machine constantly "energized" - that condition, mixed with any of quite a few mistakes or occasions, may just shock anyone.

Here is what Honeywell says, using the L4068A-series controller for instance

Connect the “hot” cord from the facility supply to the higher left terminal. On L4068, connect the fan motor to the ground terminal (marked LOAD); attach restrict transfer, if stressed in the line voltage circuit, to the upper appropriate terminal.

References Eaton, THE BASICS of LIMIT SWITCHES, [PDF] Eaton, a power management company, company headquarters in Dublin, Ireland, Tel: US: +1-877-386-2273, 800-426-9184, Canada +1-800-268-3578 International +1-828-651-0786, retrieved 2018/10/01, unique source:

Note: very good, comprehensive evaluate of wide variety of kinds of restrict switches and their operation.

Excerpt from Introduction: Presence Sensing is the act of detecting the presence or absence of an object with a touch or non-contact sensing instrument.

The sensors then produce an electrical output sign that can be utilized to keep an eye on equip-ment or processes.

Mechanical restrict switches are contact sensing devices widely used for detecting the presence or position of gadgets in industrial packages.

The time period limit switch is derived from the operation of the software it-self.

As an object (or target) makes contact with the operator of the transfer, it ultimately moves the actuator to the "limit" where the elec-trical contacts change state. Through this mechanical action, electric contacts are both opened (in a usually closed circuit) or closed (in a in most cases open circuit).

Inductive proximity, capacitive proximity, and photoelectric sensors carry out this similar process via noncontact sensing.

NORA, LIMIT CONTROLS & THERMOSTATS, [PDF] National Oil Heat Research Alliance, 600 Cameron Street, Alexandria, VA 22314 USA, Tel: 703.340.1660,

Website:, tutorial module, retrieved 2018/10/01, unique source: Excerpt:

... The National Oilheat Research Alliance, ... was once approved by Congress in 2000 to supply investment that will allow the oilheating business to supply extra efficient and extra dependable warmth and sizzling water to the American Consumers. As a government sanctioned “check-off” program, [scrape_url:1]



[/scrape_url].002 is accrued at the wholesale degree on each and every gallon of heating oil offered. While it is mandatory, the advantages very much outweigh the minimum value.

The four key fingers of NORA are Consumer Education, Professional Education, making improvements to power efficiency and safety, and Research Consumer Education lets in NORA to achieve out to the shopper and show that oilheat is a clean, safe, efficient and modern type of heating.

This verbal exchange is very important to the industry’s survival.

Professional schooling, in the course of the Technician Certification Program, supplies proceeding education, training and certification for oilheat carrier technicians. Lastly, NORA investment has helped numerous producers to expand highly efficient heating equipment, reminiscent of condensing boilers and furnaces, variable pace furnaces, variable burners and choice of different technologically advanced, extremely efficient merchandise.

  Reader Q&A - also see the FAQs sequence linked-to below

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DG along with the instance wiring diagrams discovered on this page, the IO handbook for the Honeywell Fan Limit controller is given as a free PDF download - in addition to manuals for wiring other restrict switches.


HONEYWELL L4068A,C,E,F & L6068A,D FAN CONTROLS [PDF] (1976) set up and wiring handbook.

Where does the red wire pass? No thermostat

Thank you for the replace that will perhaps lend a hand different readers as smartly. Keep me posted.

@danjoefriedman Thanks for the reply. When you discussed the handbook it jogged my memory that the previous proprietor of my area (I've been dwelling here three hundred and sixty five days) left her paperwork and I discovered the Carrier booklet for my model 58CMA oil furnace. Apparently I have an electronic fan timer (Honeywell circuit board ST9103) and the limit controls, two of them, are proven on the circuit diagram. Now I have to determine the wiring for my new primary, however no less than I'm no longer driving myself loopy trying to find a analog limit switch. Thanks again to your reply. Richard


Some forced-warm air furnaces use a snap switch or other keep an eye on to manage the fan on-off-high limits, so you would possibly not see the traditional Honeywell fan limit controller but chances are you'll see smaller, in all probability brown or black phenolic plastic "boxes" maybe simply a few inches across. There ought to be one or more fan restrict controls that might be fastened on or within the warm air supply plenum as that's the place they've to sense temperature.

So you may be able to follow wires again from the blower motor to the plenum.

Tell me the furnace emblem and model and if you don't have already got the IO Manual that would display the ones main points we may be able to supply one as now we have got a zillion heater manuals as PDFs for readers to obtain.

Hello, I've a Beckett burner (AFG) compelled air gadget that is about 20 years old. It works smartly. I simply purchased a Honeywell number one R7284U to interchange, if needed, the original R8184G just in case (it is 20 years previous, too). The outdated number one has 3 wires and the new one is extra complicated. My question: I cannot in finding the fan limit switch in my furnace. I've discovered two sensors at two places in the plenum but no fan limit transfer. I seemed within the decrease and upper compartments and in front of the blower and located a Honeywell circuit board that a purple wire from the sensors is plugged into, however no transfer as proven in all the diagrams I've seen online. I want to cord the limit into the new primary once I eventually install it. I may use some lend a hand. Numerous it. Thank you very a lot. Richard.

Thanks for the snap disc control wiring query, Gary.

Where a snap disc switch is just opening or ultimate a circuit it is typically doing so via interrupting a single wire. In that case swapping the wires is prone to have no effect at the transfer operation.

For example a transfer that opens on temperature rise will simply interrupt a burner energy circuit.

Watch out: it is not continually the case that the wire connections make no distinction on other controls or wiring connections: verify the instructions that come with the particular regulate.

For instance in some cases leaving power constantly present at the flawed facet of some circuit boards can through the years injury a board.

Another snap disc regulate example from Emerson is proven above. Notice that there is not any identification difference at the two wiring terminals.

What happens is you reverse the wires on a White Rodgers snap disc fan control?


White Rogers provides this spec - notice the voltages given [Click to enlarge any image]

Can you attach One hundred twenty volts to a 3L0 -One hundred ninety white Rogers snap disc restrict keep an eye on


Many house heating furnace blower enthusiasts run handiest at one speed.

Some have a multi-speed fan that runs at other speeds under regulate of the circuit board in the air handler, depending on whether or not you're in heating or in cooling mode.

Some air handler circuit boards certainly come with little dip switches or jumper pins that allow the carrier technician to set the fan speed(s) if the fan motor helps them.


for step-by-step instructions and for links to plenty of air handler manuals with extra instructions on atmosphere the fan speed

Here is an example for York air handlers that explains the details of environment fan speed at the regulate board

Give me the brand and model of your air handler and I will look for its explicit directions.

how do u keep an eye on the speed of your fan



The fan comes on after the plenum is warmed. Not earlier than - on a heating software.

Otherwise the unit would blow chilly air on occupants.

Where to begin: Watch the fan restrict regulate to look if it's rotating to the FAN ON place.

I installed a brand new ICM 281 for a Carrier Day and Night FAU. When I turn at the power, the blower fan began operating for 1-2 minutes, the hot floor igniter light up purple scorching, the burners ignited whilst the blower kept working. Everything seemed to work advantageous.

A couple of days later, the FAU stopped working. Shouldn't the outside igniter becomes crimson hot first, then the burners light and run for a few mins, ahead of the blower starts running to push the hot air up into the unit?

What should I check to look why the FAU stopped operating?

Thanks. J.


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Technical Reviewers & References

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Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969. National Fuel Gas Code (Z223.1) .00 and National Fuel Gas Code Handbook (Z223.2) .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. "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training subject matter] 1987 Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals, 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 about spotting problems on oil-fired heating equipment. Booklet.) Thanks to reader Dan Somerville for technical enhancing help 01/09/10 Honeywell Corporation, Minneapolis, MN 55408. Honeywell has sales places of work in all most important towns in the world and has manufacturing amenities in Australia, Canada, Finland, France, Germany, Japan, Mexico, Netherlands, Spain, Taiwan, United Kingdom, U.S.A. Honeywell Form Number 60-0450 7-75, residential department. Honeywell's latest product knowledge for this kind of keep an eye on will also be found in English at ...

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