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Bill, HVAC Technician
Category: HVAC
Satisfied Customers: 318
Experience:  15+ years service tech.
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We have a furnace that sometimes blows cold air. When it does

Resolved Question:

We have a furnace that sometimes blows cold air. When it does this we turn off the heat via the thermostat, then turn it on again, and then it blows warm air. Why does it do this sometimes?
Submitted: 7 years ago.
Category: HVAC
Expert:  Bill replied 7 years ago.
have you checked or changed your filter ? how long will it run before you notice the cold air?
Customer: replied 7 years ago.
Recently changed the filter. It never goes from warm to cold. It only happens sometimes when the furnace shuts off, and the re-starts later.
Expert:  Bill replied 7 years ago.

next time it does not light go to furnace befor cycling the thermostat and look for flashing lights in the lower door area, these are trouble codes, just count the flashes.most times the flash codes will be printed on the ignition control box.

Customer: replied 7 years ago.
Not quite sure I understand your answer. Where do I look for the codes, and what is the significance of this?
Expert:  Bill replied 7 years ago.

the codes will tell what type of problem the furnace is having.

in the lower door of the furnace there is a small plastic sight/glass hole, looking inside this you can see the led on the ignition control, it will flash in counts of one, two, three, ect...

if it flashes two times, it would mean the air pressure switch is having trouble.

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Expert:  Bill replied 7 years ago.

does this make sense?

if not let me know.