Bad limit switch

If the high limit switch was bad , the furnace should not fire. The blower will continue to run until either the system is reset, or the limit switch closes. I believe high limit switches are . This happens when the switch simply fails to shut off the fan after the burners have stopped and the air exchanger is sufficiently cool. The switch should be immediately suspect if the voltage drop is 0.

A guide to determining if the limit has failed and if so why.

This video is part of the heating and cooling series of training videos made to accompany my we.

Common Problems: 1) Bad connections at limit switch. Levers or arms not adjusted correctly to properly activate switch. Limit switch damaged – move broken, or bent out of mounting. See if there is one you can find in the fan . This is because when the furnace defaults, the fan can be used to help reduce risks caused by the problem. In this case, it would help to cool down the furnace if it has overheated.

If the blower motor blows air out the vents when manually set to ON then you know that the blower motor itself is good and something else such as the limit switch is causing the problem. Sometimes your meter may show one or two ohms of resistance due to the meter leads if it has not been calibrated to null out the wire resistance. He said however, that it is the limit switch that is turning off my burners, according to him the burners should remain on throughtout the whole cycle until the thermostat. I am assuming the problem could be with the limit switch or fan . I would just say it would be over time uses of heat on the . This video shows you how to diagnose and repair many models of Carrier and Bryant furnaces with the error Limit or Flame roll out (FRS) switch open.

There are three possible problems. The most common is your air filter is dirty and clogged. I explain the heat operated Honeywell fan and limit switch used on early gas furnaces. The flame sensor verifies that the gas has been lit.

The high- limit switch reaches its set temperature. The furnace runs until the thermostat is satisfied and tells it to shut down.