L4064B wiring for line voltageFan Limit Control Installation FAQs
Q&A on Furnace Fan Limit Controllers

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Fan limit switch wiring details: This article describes in detail the installation & wiring of furnace combination controls, also commonly called the "fan limit switch" on warm air heating systems.

The photo at the top of this page shows all of the controls and wiring terminals in a Honeywell combination fan and limit control installed horizontally on a gas furnace.

This article series answers most questions about central heating system troubleshooting, inspection, diagnosis, and repairs. We describe how to inspect, troubleshoot and repair heating and air conditioning systems to inform home owners, buyers, and home inspectors of common heating system defects.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Furnace Combination Control Fan Limit Switch Wiring FAQs

Honeywell L4064B, L4064T Fan Limit Control wiring including low voltage wires ford a gas valve, circa 1970, cited in this article (C)

These questions & answers or comments about how to hook up or wire the furnace blower fan limit control switch were posted originallyi at FAN LIMIT SWITCH INSTALLATION & WIRING - be sure to review that article.

There you will also find links to detailed wiring instructions for all brands and models of fan limit controllers.

[Click to enlarge any image]

On 2018-03-06 by (mod) - how to wire a Honeywell L4064B Fan Limit Control to Replace the Honeywell L4064-T

Yes you would either

1. simply put a small twist on connector cap on each of those individual low-voltage wire ends and tape them aside,


2. follow the wires back to their point of origin and remove them entirely. I'd do option 1. as it's simpler and fine. You could label them as "used on old Honeywell control" if you like.

You'd just connect the 120VAC wires as we've discussed.

This OPINION comes from reading about the control and what those low voltage wires were doing - as best I can see they were running a heater element in the control that in turn caused the fan to turn on "early" regardless of the actual plenum temperature.

In fact Honeywell warned that if you installed that older -T control as a substitute for other models there was a risk that it would, at the start of a heat-on cycle, blow cool air on occupants when there was a call for heat.

Send me photos of your control and the wires if you can;

Also if you have a wiring diagram for your furnace and its manual that'd be interesting to review.

You can give Honeywell a call to confirm what we've discussed.

On 2018-03-06 by Haydn

Thank you again for your prompt reply. I have a question concerning your answer. This may sound dumb, but I will go ahead and ask.

When you say, " Other Honeywell L4064x control models could still work to control your furnace, by simply stubbing off the TT wires at the control.", does "stubbing off" simply mean that I would cut the wires and cap them with a wire nut (or other means) to prevent any connectivity to the fan and gas valve via the low voltage wires?

In other words, all I need to do is only connect the 120V wires to the combination switch and disconnect and terminate the low voltage wires appropriately?

On 2018-03-04 0 by (mod) - How the L4064T turns on the fan after a timed delay


The original Honeywell L4064T 1541 control was designed to simply turn the fan on 90 seconds after a call for heat, regardless of the actual plenum temperature.

The L4064T,W,and Y models use a bi-metallic spring heater inside the fan switch to "make" (close) the switch contacts independent of the bimetallic temperature sensor probe that inserts into the heating air plenum itself.

These L4064 models needed the TT (TT = thermostat) circuit & wires to do that - using the low voltage circuit to operate the bimetal heater inside the controller switch.

From p. 10 of HONEYWELL L4064A-F, J,R,T,W,Y FAN LIMIT CONTROLLER INSTALLATION [PDF] (1985) [live link to this is given in the article above] we quote this explanation:

Operation of the L4064 Fan Limit Control - how it works:

L4064A-F,J,R -- as the plenum temperature rises, the coiled, bimetal sensing element of the control warps and mechanically makes the fan contacts (at the FAN ON temperature setting). During normal operation, the call for heat ends before the LIMIT setting is reached and the fan contacts break as the plenum temperature falls and the FAN OFF setting is reached.

If the call for heat continues until the temperature in the plenum rises to the LIMIT setting, the bimetal element will mechanically break the limit contacts and de-energize the heating control circuit.

L4064T,W,Y -- The operation of the L4064T,W,Y are the same [as the L4064A-F,J,R that I quoted above] except that the controller uses a bimetal heater in the fan switch to make the switch contacts independent of the bimetal sensing element.

This heater acts to anticipate the rise in plenum termperature and turns on th fan 20 to 90 seconds* after the thermostat calls for heat. Actual on-time will vary, depending on the voltage applied to the bimetal heater and on the temperature surrounding the fan switch.

* The fan on timing can vary depending on applied voltage and switch ambient.


Other Honeywell L4064x control models could still work to control your furnace, by simply stubbing off the TT wires at the control. That means you'll give up the heat anticipation feature provided by the L4064T but of course you could insert your own "anticipation" by simply dropping the FAN ON temperature a bit.

(To be extremely cautious about safety you should also ask your furnace manufacturer if they agree.)

You will find other low-voltage thermostat wires from the same thermostat terminals going to a gas or oil burner to actually turn on the burner.

With other L4064x control models the temperature generated by the burner then activates the limit switch.

The 1981 instructions for the L4064T (provided as a live link in the article above) point out that the L4064T might have been used to replace an L4064A or L4064B. I read that to mean that you could also substitute in the reverse direction, installing an L4064A or L4064B (or equivalent) for an old L4064T. Here is an excerpt from that document, p. 8:

Important: To [sic] L4064T uses a bimetal heater to turn on th fan 90 seconds after a call for heat. When the call for heat ends, the fan will continue to run until the fan-off temperature is reached.

If the L4064T is used to replace an L4064A or B, the blower fan may circulate cold air until the plenum heats up. No adjustment of the fan-on time is possible.

On 2018-03-01 by Haydn Chambers

I have a Rheem RGVA-09EA. The home was build around 1984 and the furnace is original. I need to replace the combination fan and limit controller. The part number that is installed is L4064t 1541.

I thought I could replace it with a "Honeywell L4064B 2210 L4064 Fan & Limit 11" 11.5" Furnace Control", but now I'm not sure. I can't figure out what to do with the two low voltage wires that appear to be in the back part of the controller.

The L4064B only seems to have terminals on the front. The connections you show in your instructions do match the front part of the existing L4064t. The small red cardboard tag is even still in place. Can you give me some guidance?

On 2018-01-16 Sean grisinger

What ended up being the problem ? Have the same issue

On 2017-11-23 by (mod) - The Honeywell L4064B222 is a "universal replacement" for older fan limit controllers


The Honeywell L4064B222 is a "universal replacement" for your older L4064W1080, as you were told.

The controller includes three wiring terminal options so that the controller can be easily connected in a variety of situation.

The controller also includes female wire receptacles at the upper sides used to power an auxiliary device like a humidifier.

Most-likely for your application you only want to connect two wires, the two line voltage wires that operate the blower fan as shown in Honeywell's wiring diagram and instructions.

I would leave the two other wires disconnected.

At the REFERENCES section to this article below we include a link to the older installation manual for this control. I will update the article to be sure that both the older and the most-recent wiring instructions are given as PDF files at the end of the article text above. You may need to clear your browser cache to see the updated article).

On 2017-12-08 16 by Andy

I have an old furnace and need to replace a Honeywell L4064B1295 controller what new part number will replace this old one??

On 2017-11-23 by Tom

I bought a replacement for my L4064W1080. Was told the L4064B2228, is the replacement for it. There 2 spade connectors on the W1080
that are not on the B2228. The other end of the cable is connected to terminal block. Can they just be jumpered??

On 2017-11-11 by (mod) - no response from the thermostat

John, if you think the problem is in the fan limit control then the next article in this series contains diagnostics for that issue


On 2017-11-1 by John

I am having the same problem with my heater as Peter in his earlier comment. I am having no response from the thermostat. I have replaced the fan control box & thermostat control box.

On 2017-02-16 07:28:46.594368 by Peter

I have a oil furnace that starts the blower when ignition and turns off fan when limit reach 180 with no power for fan motor have to wait till limit goes to 100 then starts up again thermostat have no control to start or to stop furnace

On 2017-01-08 by (mod) - skip the low voltage wires that operated the heater in the L4064-T

Joe, and Miguel,

You can skip the extra two wires but will probably find that one of the following furnace or heating system features is then not working:

1. a pre-heater installed in the furnace may have been installed to cause the blower fan to start sooner - speeding the heat delivery before the furnace air is fully warmed

2. some old Honeywell (L4064-type) switches use the wires for a separate humidifier or dehumidifier.

Be sure that the sensor for your replacement fan limit switch is the proper size, as a wrong length could make the system work improperly or might be unsafe. For example a sensor that touches the supply plenum cabinet won't function properly.

On 2017-01-08 by Miguel Burgos 1/2027

On January 5 2016 Joe wrote a comment here and I have the same Honeywell fan/limit switch for my old furnace (Rheem) with the same six wire set up, can someone please answer comment

On 2016-11-25 by Sweeny

How do I remove the Jumper to hook up a thermostat on the Honeywell combination furnace control on a L4064B

On 2016-01-05 by Joe

I have an old fan/limit switch from Honeywell that has an additional 2 wires (6 total). The 2 wires are yellow and the schematic shows one going into the fan limit switch in the bottom/center, goes through a heating resistor/fan assist, and exits.

It is in parallel with the safety and gas valve circuit. It is diagramed as a resistor but is called my the 2 names, heating resistor & fan assist.

The replacement fan limit switch does not have these extra 2 connections and is similar to yours on this page. Are these 2 connections necessary? Can I just short them or bypass them? Cannot find any info on this.

Question: How do I wire a furnace fan relay switch

how to wire a fan relay switch - Kenneth Sanders 10/7/2012



Question: hook up my air conditioner to my gas furnace

(July 24, 2011) MEHMET said:

Hi see if you could hlep me I have a gas- furnces model ghs-100 can I hook up my air conditioning to it



I'm unclear just want you are trying to do; it sounds to me as if you need an on-site trained HVAC technician.

Question: where to connect the black wire coming from my Honeywell Fan Limiter switch

(Oct 4, 2011) Weeks Parker said:

Please tell me where to connect the black wire coming from my Honeywell Fan Limiter switch, model L4064. It goes to the 24 volt relay, but I do not know which terminal to connect it to. Does it go to the armateur or to the top or bottom terminal of the single pole double throw relay. or does it go some place else?


Weeks I don't quite understand the options in your question, but indeed the typical fan limit switch wiring is described and illustrated with schematics in the article above as well as in the installation pamphlet for the fan limit switch and usually also right inside the limit switch cover itself.

I'm always nervous about giving very specific wiring instructions like "where do I connect the black wire" because being offsite and just reading someone's message I have no confidence that I know for sure how the "black wire" is connected at its other end.

Question: which wire (black or white) is the line voltage and which one is the load voltage for the fan?

(Mar 26, 2014) Ralph-NY said:

How do you determine which wire (black or white) is the line voltage and which one is the load voltage for the fan.

How could I check with a multimeter?

Reply: black for line and white for load


by convention we use black for line and white for load.

To check, and provided you know how to use a DMM or VOM safely, one could check for voltage on either wire. The one containig voltage is the "Line" wire.

Start with a simple neon tester for voltage as discussed at

Question: wire a woodfurnace 1st stage heat and 90+ gas furnace second stage heat with ac system on the gas furnace

(June 8, 2014) Paul Black said:

need to wire a woodfurnace 1st stage heat and 90+ gas furnace second stage heat with ac system on the gas furnace

I need to wire to one t-stat (both have transformers) and have both fans running when a call for heat or cool or fan on.

Wood furnace has an inducer motor and blower motor hooked to limit switch. Do you have a wiring diagram I can use

Question: DIY Honeywell Combination Fan & Limit Controls on Warm Air Furnace model number L4064B2848 installation

(Nov 5, 2014) Anonymous said:

Hi my dad has a Honeywell Combination Fan & Limit Controls on Warm Air Furnace model number L4064B2848 but im looking for it on amazon ebay and other sites and keep coming up with no results page. why can't i find this model ? and is there other model that i can use thats the same as that model?

im going to have my friend install it but before i buy it if i can find one.. i want to make sure im buying the right part.

i can see the flame and i can hear the fan spin but theres no warm heat coming out of the heaters and my dads home is cold :( we cant control it from the thermostats and the scale plate isnt moving anymore? please help me out


(Nov 7, 2014) (mod) said:
Anon with apology for sounding a bit like a smart alec, I suggest that you want a trained heating service tech to inspect and repair your dad's furnace. We don't yet have a diagnosis of what's wrong, so I can't assume that the fan limit switch you want to replace is even the culprit.

If the burner runs and the blower fan operates, I don't start by suspecting the fan limit switch. More likely I'd expect disconnected, crushed, or collapsed air ducts to explain why no air is being delivered.

Question: installing a coal stove beside my "propain" furnace

(Nov 16, 2014) Al said:

I'm installing a coal stove beside my "propain" furnace with an enclosed hood over it & ducting it into my cold air return.

I want to install a fan limit switch over the coal stove & wire it in parallel with my furnace fan limit switch so that the new limit switch will run the furnace blower to suck in the warm coal stove air thru the cold air return to circulate it thru the furnace air filter & throughout the house.

I want the set-up to enable either limit switch to control the furnace blower when they sense enough warm air & the demand for heat at the thermostat.

This should be a simple matter of wiring to the power supply & connecting jumper wires from the furnace switch limit side terminals to the coal stove switch limit side terminals.... correct? If not, please advise the correct way to wire the coal stove limit switch to work as expected.

I read my question after I posted it and realized that I hadn't mentioned about connecting a jumper wire between the fan side terminals too. Below is how my question should have read:

This should be a simple matter of wiring to the power supply & connecting jumper wires from the furnace switch limit side & fan side terminals to the coal stove switch limit side & fan side terminals.... correct? If not, please advise the correct way to wire the coal stove limit switch to work as expected.


Watch out: When you use a heating control in any application not intended by the manufacturer your system could be unsafe risking a building fire or death. So if I were doing what you suggest I'd start by giving Honeywell technical support a call to ask if they agree with the approach.

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Continue reading at FAN LIMIT SWITCH TROUBLESHOOTING or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see BLOWER FAN OPERATION & TESTING if your heating or cooling system blower fan itself appears not to be working,

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Articles on the Furnace Fan Limit Switch

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