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M Oglesby
M Oglesby, HVAC Technician
Category: HVAC
Satisfied Customers: 2038
Experience:  Universally Certified HVACR Technician
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Why is my furnace blowing cold air?

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My furnace is only blowing out cold air, what could the problem be? I have a Lennox Elite Series model C23-41W-1 that is about 13 years old. I have tried turning the switch of the furnace off and on. I have also switched off the breaker and switched it on again.

M Oglesby :

Go to the furnace and look to see if there are any flashing lights on the control board. If so, what pattern are they flashing in? 1 flash pause, 2 flash pause, 3 flash pause, etc...?

JACUSTOMER-yeuoxiob- : no flashing lights anywhere inside or out - when I open it up the large cylinder unit at the bottom shuts off
M Oglesby :

When you open it up, hold in the door safety switch with your hand and observe the ignition process. Tell me if the burners igniter or if the igniter attempts to ignite. Hold the button in at least 3 min. If you have to, tape the switch down.

JACUSTOMER-yeuoxiob- : nothing happens - there is no ignition
M Oglesby :

do the lights light up? Do you have the thermostat set to turn the heat on?

JACUSTOMER-yeuoxiob- : yes and its set to 80 now but its 62 in the house
M Oglesby :

And it is not doing anything now?

JACUSTOMER-yeuoxiob- :

It's blowing cold air - There is no flam.eTthe only thing that is running is the cylinder at the bottom of the furnace and that is only on when I hold the button in or have the panel in place.

M Oglesby :

It sounds like you have an open limit switch. There are two kinds of limit switches. The first that we will try to locate is the Main Limit Switch. We need to locate it and bypass it to test it. It is usually a rectangular or square looking device that has two wires attached to it and is usually located inside the furnace cabinet on the back panel wall behind and above the gas valve. It is usually about 2 inches X 3 inches. Locate it and let me know when you find it. You will have to remove the top panel door.

JACUSTOMER-yeuoxiob- :

Hey M - Sorry I am at work right now and trying to work through my wife, but she is balancing 4 kids at home - If I can have her try to locate it I will, otherwise this may have to wait until tonight. Do you think I need to call a tech to come out? If it is an open limit switch is that something I can replace or would I need a rep at that point?

M Oglesby :

You can replace it. Replacing it your self will save you $200. If that is the problem.

JACUSTOMER-yeuoxiob- :

Ok - Very nice! I will let you know if she can help out - Thanks again!

M Oglesby :

You are welcome

JACUSTOMER-yeuoxiob- :

I think I can remember seeing that box - once I locate what should I do to test it?

M Oglesby :

You will have to remove the two wires and attach or jump them together. While they are attached, attempt to turn the heat on.

JACUSTOMER-yeuoxiob- :

It worked!! What do I need to buy to fix it and where can I buy it?

M Oglesby :

Great Job! You will need a Main Limit Switch. You can get one at any HVAC Supply store or you can order one online at www.AmericanHVACparts.com Have model number, serial number, and part number of old limit if possible.

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