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Fan will not turn off

I need to adjust the limit switch. How do I turn off power to heat pump before removing control cover?

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You should have a power disconnect within 10 ft of the unit.

Follow the high voltage power wire. The box you are looking for is typically gray brown or black, has a small door that flips up, and either a pull out switch or a breaker style switch inside.

They are usually mounted on the wall of the house near the unit.

Sometimes they are found in an outdoor panel box near the meter. Those are breakers.

Always test for power after turning it off just to be sure.

Posted on Dec 25, 2008

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Our Panasonic Heat Pump refuses to turn on. Can you help.


More than likely there is a power related issue within the furnace or the heat pump... Control power for the heat pump originates from the furnace control transformer. If you turn the thermostat fan setting to the 'on' position and the indoor fan comes on, the control transformer is delivering 24v control power to the thermostat circuit. If not, there could be an issue to resolve first. If the blower does come on, that's kinda good but it then means there could be a power or control issue within the heat pump itself. Any issue within the heat pump beyond making sure the 240v applied voltage is at the unit will usually be beyond the average homeowners capability to resolve.

I know this isn't much to go on, but there is such a tremendous volumn of issues that could be effecting the systems operation it would take pages to just scratch the surface. You are going to be limited to checking the basics, then my suggestion is to call a reputable service organization to resolve the issue.

Dec 27, 2014 | Panasonic Air Conditioners

1 Answer

My furnace is an older type furnace and it was working fine yesterday but the blower won't shut off after it runs for a while it run continueally I was wondering what I could do to fix this pr


When you say 'older furnace' I am assuming old enough to where there is no circuit board. They will usually have a thermally activated 'fan-limit' switch with a bi-metal sensing device. Most older furnaces had either a Honeywell or a White-Rodgers controller and they look almost identical. With the furnace door off, look towards the top of the furnace vestibule (above the flame area) for a rectangular box approximately 3 1/2" wide by 5" long. Tap the side of the box with a screwdriver and if the thermostat setpoint has been satisfied and the gas burners have been off for more than three minutes, the fan should then shut off. The switch contacts are either stuck together OR the bimetal sensing device is weakening from thousands of cycles.

If it continues to run, squeeze the sides of the 'lid' of the box and remove the cover. Inside you'll see a round moveable dial with three pointers, marked 'fan off, fan on, and limit'. The 'limit' should remain at or near the 200 degree setting, the 'fan on' can be anywhere around 140 and the 'fan off' can be anywhere near 100 degrees. It is the 'fan off' position thats giving you the grief.

Turn the thermostat up again and sit there and watch the dial do its thing and yo'll understand better how this control works. Watch it rotate past the 'fan on' setting and observe the fan turn on. Turn the thermostat below room temperature and watch the gas shut off and the dial rotate back towards the 'fan off' setting. If it hangs up again before twisting past the setpoint, you can slightly increase the setting to compensate for the weakening bi-metal element. But just a tiny bit, not a great amount or you will have the fan shutting off with a lot of residual heat still in the heat exchanger. The idea of the delay in shutting off the fan is to remove all that residual heat and transfer it to the house.

There are other brands that utilized 'timed on' fan controls, and there are a few other variances of controllers but what's described above should cover the vast majority of older furnaces.

Remember there is ELECTRICITY inside the fan control and any adjustments should be done with the power OFF !!!!

Dec 26, 2014 | Air Conditioners

1 Answer

Furnace turnoff just before the blower go on.


You are to be commended for noticing this sequencing of events-- Good observation!

You need to adjust the Plenum control switch. (Or fan control switch)

Usually at the top front of the furnace, is a Fan control switch--
It is called the Plenum switch-- and it senses the temperature of the Air being heated by the fuel--
(Is your furnace Oil or gas?-- if Gas-- is it LP or Natural?)

This switch Has a cover that can be removed-- inside is a round dial, with some adjusting screw, and Degrees stamped on the perimeter of this round dial.
You can take the cover off, while the furnace is running-- (Just do not touch the screw terminals that have electric power to them--
You can rotate this dial, and it will turn the fan on-- (Or if the trip levers are mis-adjusted-- it might shut off the burner-- just rotate back the other way, and it will re-light etc.--
The purpose of this control is to make sure your fan is not blowing COLD air.
So-- lower the 'ON' switch tripper, down lower, so the fan will turn on sooner.
You may have to loosen a set-screw-- but usually they are just friction held-- and can be forced to slide (rotating CCW) to the lower temperature setting.
(If you get it too low, it will be blowing cooler air than you like at the registers.)

However-- to get the most heat from your furnace energy source-- you want the fan to come on as early as you can tolerate-- That will be delivering HEAT to your occupied space sooner, and giving yo more of those dollars you are spending on fuel, in the orm of heat in your house!

Tell us more

Mack B

Dec 28, 2010 | Air Conditioners

1 Answer

I have an early 80's mobile home with an "intertherm gas atmospheric furnace" pilot light is lit but can't get the furnace to "fire". Seems as though the limit control is stuck open. ...


If your pilot light is lit then I would first check your thermostat. Make sure it is on heat setting and fan is on auto, turn stat up to where it should be calling for heat. If you don't get burner to light remove front cover from thermostat and see if it has a mercury switch, if it does move temperature selector up and down and see if you can see a spark in mercury switch vial. If y ou cannot see a spark remove screws that attach t-stat to base.Remove carefully and disconnect wires that go to r and w terminals on stat base. Temporarily connect these two wires together. This should make burner light if you have power to thermostat. If burner does light disconnect wires and replace thermostat. Also if you have a volt meter check across these two wires and see if you have power there. Should be around 24 volts a.c. If your thermostat has a fan on setting try that. If fan runs you know you have power to furnace The gas valve needs 24 volts to operate and inside the electric control box in furnace there is a transformer to step down 110-120 supply voltage to 24 volts. If transformer is working you should be able to hear a low buzz or humming sound. You can also check across gas valve terminals when t-stat is set for heat, you should read about 24 volts. If you have 24 volts to gas valve and it is not opening then you need to replace gas valve. The main purpose of the limit switches is to turn blower on when temperature in heat exchanger reaches fan on temp,shut off blower after burner shuts off and heat in heat exchanger reaches fan off temperature, and limit if temperature exceedes set point without blower coming on. I hope this helps you. Thanks

Nov 25, 2010 | Air Conditioners

2 Answers

Blower continiously running...switched out fan control brd, still runs...rmoved all t stat wiring and still comes on


Hi, sounds as though your at the end of your rope!! Yes, this can be a ***** to figure out. So, you replaced the main control/blower board, and removed all stat wires at the stat. I don't know if this is a split gas heat and cooling unit or a heat-pump or the age of the unit? On the blower board, did you remove the stat wires on it first before you took it out and the fan kept running? Or did you switch it out by doing one wire at a time and then putting the stat wires on the new board. What I am trying to find out if you remove the green wire now at the board, have you tried this to see if the fan stops? I'm just trying to rule out any stat wires touching at either end or in the wall causing the fan to run, but I don't believe this to be the problem. Depending on the unit if it has a gas furnace or heat-pump, you need to go to the fan limit control. If it is a gas furnace, you have a fan control that has stuck contacts causing the fan to default and run. If it is gas and a older unit, it will be a Honeywell type with a chrome box on it. Behind the cover is a switch, fan control switch that brings the fan on and off. It rotates and they will get dirty and stick. It will need to be removed a cleaned with a old tooth brush works well. If you have a heat -pump, no gas indoor unit, look for your fan time delay relay. Look on your schematics and it will show you where its at on the unit. It is most likely the cause, burned or contacts welded together. It will say TDR on the schematic. It will send 24 volts to another relay where one leg (hot wire ) that your fan connects to all the time causing fan to run. If I were there on site, with a few checks with my meter would have you on your way, but I'm not. Also. there is a small round fan limit which depends again on the type, that is located on some up by the blower motor with a wire in and out and has a fan reset button on it. By resetting it, it opens the circuit shutting down the fan. Check these things out and keep me posted. If you will, please tell me more on the type of system it is you have. This will make it much easier to trouble-shoot. Please let me know and please be kind when rating me. I thank you for this. I hope I have been of some help to you. I will be here for more help to you.
Sincerely,
Shastalaker7
A/C & Heating Contractor

Jul 01, 2010 | Air Conditioners

1 Answer

I have a Rheem model RRGG 05N37 JKR Serial # AYA4785 manufactured in 1993. I have to replace the fan limit switch. Is the Honeywell L4064B2210 Fan/Limit Control Switch the correct one?


Typically any fan limit switch will work as long as it is the same length as the old one and is in temperature range as well as covering the hole that the old ond came out of. it the screw holes do not line up, besure to put a screw into the exposed holes to prevent heated air from leaving the cabinet

Oct 21, 2009 | Air Conditioners

3 Answers

Code #33 on Bryant 355MAV 90i Furnace


'Limit or flame rollout switch is open'. In my case, the flame rollout switch had tripped due to an overheating? I had to push the button between the wire leads to reset the switch. Then when I turned the power back on, the furnace started up like normal.

Why did the switch overheat and trip? My current theory is that there was a rubber grommet around a pipe near the switch that had slid down and was no longer sealing the furnace?

Mar 01, 2009 | Goodman CLJ30AR32 Air Conditioner

1 Answer

I need to adjust the limit switch on a Lennox heat pump. How to I turn off power to unit before I open the control cover?


If you mean the ambient lockout switch it shpopuld be oin the outside unit and all that you will need to shut off is the outside condenser before you open the panel. ther is a disconnect that you will have to throw either right by the unit or inside of a main breaker panel.. Hope that this helps and Thanks for using Fixya

Dec 25, 2008 | Air Conditioners

1 Answer

We have a coleman evcon furnace. The furnace runs constantly. It'll get to the temperature but then the fan doesn't quit and it only blows out cool air the the reset switch pops up and needs to be be...


It sounds as if your furnace is exceeding the limit tempperature of the manual reset switch. The coleman is designed for the fan to continually run when this limit switch is tripped in order to keep the heat exchanger cool.( it is a safety feature) afew things may be happening.
1. the manual limit switch( the one you have to push) may be defective.
2. The fan may be running at too low of a speed. Turn power off at circuit breaker. locate circuit board on the board there will be one terminal that says heat if the red wire from the blower is on it tthen you may need to up the speed. follow the wires from the blower to the board if it has multiple speeds then you can isolate the red and put the blue or orange on the heat terminal.
3. the board may have an adjustable fan on and fan off pin selector if it is set up to come on to long or go off to soon it may not be controlling the temp of the heat exchanger properly.
4. I would also suggest checking to see if the orifices and gas valve are set up for your sytem correctly.
these are just simple ideas let me know how things go.

Oct 15, 2008 | Air Conditioners

2 Answers

Air Conditioner malfunction


Hi, Sounds like you have a short in the control circuit to me. Turn off all power going to the unit. Write down or otherwise mark the wires leaving the control board going to the thermostat. Remove them from the control board. Replace the fuse. Turn power back on and see if the fan still runs. If it does, check and or replace the heat limit switch that brings the fan on during the heat cycle. It may just need adjusted. If the fuse blows, I would think that the control board is probably bad. If it doesn't blow, Remove the thermostat. Leaving all thermostat wires open check them with an Ohm meter. There should be no continuity between them. Twist all the wires together at one end and ohm them again at the other end. You should have complete continuity on all wires. If the wiring checks out, down power the unit. Double check your wire colors and rewire the control board. With all wires open at the thermostat, turn the power back on. Touch the RED wire to the YELLOW wire. The Condensing unit should come on. Touch the RED wire to the GREEN wire. The fan should come on. Touch the RED wire to the WHITE wire. The heat should come on. Down power the unit. Replace the thermostat. Test unit. If the fuse has lasted ok but blows now it is either wired wrong at the Thermostat or the thermostat is bad. I hope I have helped. NOTE: If you can not understand these instructions. Call a licensed Heating / Air conditioning company. kstfas

Sep 23, 2007 | Air Conditioners

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