In the cold weather, it is important to have warm air in the house. Occasionally problems may develop with your heat system. You may notice your Lennox furnace blowing cold air. You will want to investigate what is happening and why.
Checking the burner
Observe your unit as it kicks on. Is the burner lighting? If so, there are other things to look for. Here are a few suggestions.
There can be a lot of different things that will affect the heat. Try to think of the simplest solutions first. Is it early in the season? You probably have a central air unit that uses the same blower motor.
Most blower motors have speed control settings. In the summer, you want to have the blower on high mode. This will give you maximum cooling capacity.
In the winter, the blower should be set for a lower speed. This will make the air warmer. If it is too high, the air may feel cool or not as warm. Check to see if the blower is set on high.
Many units are not difficult to check. You need to kill power to the unit first. Pull out the blower unit and follow the wires from the motor. Do they go to terminal screws?
In some cases, all you have to do is change the wire set up. There should be a diagram or printed words on the unit.
Some newer models use electronic controls. Check with your owner manual. It may have instructions for blower speed settings. After you make sure that the speed is low or medium, you can proceed to other things.
One important component is the limit switch. It is located in the plenum. It is heat operated. When the temperature of your plenum reaches a set point, the contacts will close. This sends power to the blower motor.
If the blower motor comes on too soon, the plenum will not be hot. As a result, the air may feel cool. Check to see if the setting on the limit switch has been changed.
Observe the unit when it comes on. Does the blower come on right away? Does it appear to be coming on too soon? Try raising the temperature setting on the limit switch. This may give you warmer air. If not, you may need to have someone check your unit.
Is your Lennox furnace blowing cold air? Check to see if the burner is lighting. If it is, check the speed setting on the blower motor. It should be on medium or low.
Check the setting on the limit switch. You may need to raise it. If that does not work, it may be best to call for professional help.
Originally posted 2010-09-10 04:52:07.