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I have a lennox pulse 21 And if i set the thermostat to auto the unit kicks off after a min and the limit switch goes over 200. But if i keep the fan on the unit works fine.

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See if you blower speed is set to low speed in the heat mode.
I think what might be happening is the blower is set to low speed in heat and when you switch to automatic, the blower is switched to high speed. You may have to change the blower speed to high in the heat mode. If not you may have an airflow problem such as a Dirty filter, ducts not sized right, dampers on the room outlets closed.

Posted on Dec 17, 2016

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Posted on Jan 02, 2017

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My honeywell Thermostat reaches the heating temp. but the fan will not stop running.And yes the fan is set to auto.It just keeps running and running and running.It stays the same temp but will not shut off...


I want to give a simple explanation before I go any further. On the heating side of a unit even though tthe temp has satisfied the thermostat, the fan will run until it cools down the plenum where the air flows from the air handler. There is a bimetal switch called a fan limit that operates the blower when the plenum reaches the temp set on the fan limit switch. Now if your fan keeps running even after the plenum chamber has cooled down, then you could have a fan limit switch that is stuck in the run position and must be replaced in order to correct the problem.

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I have a Lennox Pulse G21 that the blower stays on constantly, even if the thermostat is turned off with the fan setting to auto. The light indicator inside furnace is green and I have already replaced the...


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Expensive is relative, service calls are never free. But if you have an idea what the problem is, you are armed against an unethical service company. Now to what you describe, could be a couple things, first let me explain the difference in fan speeds. Furnaces that both heat and cool have multi-speed blower motors. High speed is for cooling and lower speeds are for heating. The fan switch at the T-Stat turns on the high speed fan relay. The lower speed fan is turned on by either a temperature activated switch (silver box mounted on front on furnace above burners) or a time delay relay which is solid state. That being said, your problem could be a defective fan switch or one of your blower motor windings has gone bad. Most motors have 3 or 4 speeds and a technician could just change speeds and all would be good. A fan/limit switch is not so expensive that you would replace the unit. Bottom line, unless your really handy, a heating company is in your future. Good luck and please rate my answer if it was helpful to you.  

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