Air Conditioning - Blower fan will not shut off

I have a Lennox central air system. The blower motor continues to run at low speed, even after the compressor has shut off. When the compressor kicks in, the blower goes into high speed. I have completely shut off the air at the thermostat, but it still runs. Any suggestions?
Thanks for your help.

You may want to 1st check the safeties in the furnace or you may have a fan relay that is stuck.

Gas furnace? If so, Mattison hit the nail right on the head.

It is a gas furnace. What is the safeties and where would I find it. Also how could I check the relay? Thanks

Just about all modern gas furnaces are configured such that, if the high temperature limit in the furnace opens, the blower will run full time. So that is the thing to check especially when considering the way the fan motor changes speeds when the cooling unit comes on. I doubt it is a relay problem. Most likely your furnace has a circuit board that includes the fan, safety and gas valve functions all on one board. You'll have to trace out the wiring diagram to locate the limit switch. Did you have any problems with the furnace last heating season?

We didn't have any problems last winter. The unit does have a circuit board. In the wiring diagram it identifies a switch-continuous blower. Is this the one that you would expect to be bad? This blower issue started a couple of days ago. Is this something that needs to be fixed immediately or can I take a day or two and try to figure it out? Is there a chance that the blower will burn out by constantly running?

Unless high and low speed are both getting power at the same time you're ok. Look on the diagram for a high limit or roll out switch and check these. On some Lennox units just turning off the main power to the airhandler will reset them.

I'd like to find the limit switch for the blower. Where would I find this? I also looked at the control box. On this board there are 4 covered switches. In the owners manual they are labeled "BCC2 Blower Control Center". Are these relays? When I turned on the power and the fan came on, 3 of the 4 switched and the 4th remained the same. Let me know. Thanks for your help :confused:

It should just be a small disc type device with 2 wires on it. You will have a couple right there by the burner area those are roll out switches and then up about a foot or two there will be one right on the furnace wall. That will be the high limit. Sometimes they will have a little red reset button right in between the two wires about the size of a match head. You can temporarily for testing purposes only jump these out to see if they are giving you the problem. If they are have your furnace cleaned and safety checked.