The limits on my limit control can not be moved. I tried to hold the dial and slide, no luck. I tried to hold and use a screwdriver to push them, no luck. Are they locked in place, i.e. Need to push them in, pull out, etc before sliding?
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Re: Can not adjust limits
Try sliding them in, if they refuse to move, I would recommend replacing it, they are not to costly, and a new one would be more of a beifit than a henderance, sometimes the old ones get a little rusty inside and will not move, they should move rather eaisly, hope that helped, please leave a feed back, thanks
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take cover off and hold round dial so it dosent move. there are 2 tabs in the dial . the one on the left is the low limit. the one on the right is the high limit.high limit is when the furnace shuts down 200. the low limit is when the blower will stop 90 to 100 degrees.
First thing I would suggest just to be on the safe side before you began shut power off to unit.
Remove cover on combination fan and limit.
I would set the fan on at 130-140 and fan off at 90-100 degrees. When you adjust setting grasp the outside of the dial to stop it from rotating when you are moving set point indicators. Replace cover and turn power back on. I hope this helps you. Thanks.
For most applications I would set fan on at 140 Degrees, fan off at 90 degrees and fan limit should be either factory at 190-210 or I would set it at 190. When you are setting set points on dial you should hold outside of dial so it can't move and set inner indicators where you desire. If you want you can vary by a few degrees but I would not go below 90 on fan off or above 140 on fan on. Possibly 100 and 120. Hope this helps you. Thanks
Most furnaces are equiped with a two speed blower. Hi speed is controlled by a relay sytem initiated by the thermostat. short of a stuck relay, hi speed should not remain on unless your thermostat "fan swith" has been moved from "auto" to "on", if this is the case turn the switch to "auto"
Low speed is controlled solely by the furnace itself. Depending on the age and brand of the furnace it is either brought on by time or temperature.
From your description of "tapping the relay of the limit switch" I assume you have an older furnace with a combination fan/limit control. The most common of these were a grey box with a removeable rectangular lid. In some cases there was a (commonly white) switch poking through this cover which you could manually turn low speed on if you pushed it in, make sure it is pulled out.
Otherwise the switch is refered to as a bi-metal limit. When heated the two dis-similar metals (coiled together) expand and contract at different rates. When the furnace cycles on, the metals heat and, due to design, twist a dial, which you should be able to see under the rectangular lid. The dial should have three pin settings for the purpose of switching. the lowest setting, usually around 105, is the fan OFF setting. The second, usually aroun 135, is the fan ON setting. The highest should be fixed around 250 it is the high limit and should not be part of your problem.
....After your thermostat has been satisfied and the flame shuts down...you can physically watch that dial move clockwise and hopefully reach the setting of around 105, unlesss that setting is set below the temperature of the room the furnace is in (try setting this setting higher to see if it helps).
(make and age of furnace helps a lot with trying to trouble shoot, also is it a mobile home unit?)
Chances are you ahve a bad fan limit switch. If it is adjustable try to adjust. Set at 90 and 120. If it is off a little move the temp up a little. Should have slide dial under the lid on the fan limit. Keep in touch Rus
Hi, Yes, you have the answer to you're problem. Now, I don't no if you have just a high limit, or a combination Limit control? I will go with the combination fan control as when they go bad, they stick in the closed position and they have normally open contacts. When the heat exchanger starts to heat on a call for heat, there is a dial on the fan control with temp. settings on it , and it will start to rotate as the heat gets higher. When it reaches its set fan on temp, it with start the fan.We no the fan works so the blower is good, so it shuts the burners down on you're high limit temp. which is factory set to about 250*F. When you turn The t-stat from auto to on in the fan side, that solves the problem temp, only. You will need to R & R the Fan control. If you need some direction on doing this please let me know and if it is a Honeywell auto/on type that is rectangular in looks, and if you remove the cover you will see the temp. dial with arrows on it. Thank you. Best of Luck, and Sincerely, Shastalaker7
there are 2 5/16 screws that hold the housing whitch will then slide out. but you may have to remove some of the wiring on the control board mounted on the front of the housing or remove the 4 5/16 screws holding the control mounting plate to the blower housing. also.be careful not to damage the limit switch thats in the way of it sliding out
first try to pull the little white button out, it is a manual control button, and the out position is auto. If that does not work try taking off the cover, lightly hold the dial down while you adjust the settings. they are on the side of the dial, first setting is the off pos. set to 90, second is the on pos. set to 125-135. then put cover back on, while being careful not to push the button in.
I am providing some information, but I encourage you to have a furnace technician look at your furnace. The reason is; the limit switch trips when there is a problem that may present a fire or combustion hazard. I've seen these switches go bad, but not very often. Usually they are tripping because the plenum is sooted up and excessive heat builds in the combustion chamber. This is common in older furnaces that have pilot flames- the flame runs all year and soot deposits in the plenum, plugging the air flow through the combustion chamber after years of use.
The limit switch is a safety control switch located on the furnace just below the plenum. If the plenum gets too hot, the limit switch shuts off the burner. It also shuts off the blower when the temperature drops to a certain level after the burner has shut off. If the blower runs continuously, either the blower control on the thermostat has been set to the ON position or the limit control switch needs adjustment. Check the thermostat first. If the blower control has been set to ON, change it to AUTO; if the blower control is already on AUTO, the limit switch needs adjusting.
To adjust the switch, remove the control's cover. Under it is a toothed dial with one side marked LIMIT; don't touch this side. The other side of the control is marked FAN. There are two pointers on the fan side; the blower goes on at the upper pointer setting and turns off at the lower pointer setting. The pointers should be set about 25 degrees apart. Set the upper pointer at about 115 degrees Fahrenheit and the lower one at about 90 degrees Fahrenheit.