Question about Heating & Cooling
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Posted on Jan 02, 2017
You have a limit switch located in the furnace (a little bigger than a dime and located near the center of the front panel, sometimes the switch is mounted to a small fiberglass board) . There will be two wires going to it. They sometimes trip so often that they fail to automatically reset(due to dirty filters or undersized ductwork). You can SHUT OFF POWER TO THE FURNACE, then remove the two screws holding the switch in the furnace, pull the switch out of the furnace and tap on it and wipe it off.
The switch may work a few more times but should be replaced with the same size and type. You will see some rating printed on the switch somewhere. Write down all the numbers and get a replacemet from a furnace/AC supply house. If you have a meter and know how to use it you could check the switch for continuity.
Sometimes just a tap on the switch will get it going. There will also be a couple of rollout switches that could be tripped. They have little buttons on them to reset them. If they trip it may have other issues to be solved.
Hope this helps!
Posted on Feb 01, 2009
SOURCE: Main limit switch
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.
Posted on Mar 15, 2009
SOURCE: open limit switch
Tjere is a limit switch that will only allow the durnace to reach a certain temp by kicking on the fan. The thermostat being unable to read the temp affects its ability to keep the furnace from exceeding your settings. *Advise not to use until corrected. Both limit switch and thermostats are inexpensive and simple to change. If in doubt, call a heat and AC tech to repair.
Posted on May 20, 2009
If it is a down flow, it will usually be found in the return air plenum just above the blower. You need to remove the front panels and look inside above the blower. You may need to remove a second door to access the blower section. If it is an upflow, remove the bottom door and look alongside the blower where the return air comes in.
Posted on Oct 04, 2009
A pressure switch is a safety, which in this case is being used to verify that your furnace is drafting properly. Yours in particular is sticking in the closed position even after the call for heat is satisfied. The control board checks to make sure the switch is open the next time there is a call for heat, and when it sees that the pressure switch is already closed even before the draft inducer motor comes on, it knows there is a problem....hence the error code. When you are rapping on the furnace, it is causing the contacts to open, eventhough you're not tapping on the pressure switch itself. Usually you will see a rubber hose attached to the pressure switch and 2 or three wires depending on what type of switch it is.
I hope this helps!
Posted on Oct 29, 2009
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