When furnace is off - air flow reverses ???

[verhoff]

Rather odd situation this is the 1st heating season since moving into our new place. The house is only 8 years old. The AC last winter didn't work well and I had the freon recharged but still the unit ran forever on hot days.

Anyhow my issue with the furnace....when you turn it off....cold air flows from the cold air return vents. And there is a vacuum on the exhaust vents. I've held a piece of paper by all the vents to confirm and they all act that way. It's fine when the furnace is running, but when it's off it pumps a quite a bit of cold air thru the returns.

Read somewhere that there may be a damper or something stuck?? Have no idea. I've been in the attic and things seem secure and sealed. Oddly if our thermostat is selt for 70 or less the house seems cold or chilly but at 71 degrees the house is toasty.

I'm confused so any help would be great. Thanks.

[mrkool]

Well, the first thing that came to mind is the blower running backwards when system is off, I've found that a couple times,
turned out to be a bad capacitor.

But this is different in that your getting cool air from the return when the system is off, but also, some pulling of air in at the registers.

the only dampers that you should have are at the start of each branch line going to individual vents, although I did find one in a 16" return duct last month, no wonder the unit needed replacing.

You definitely have an issue with outside air getting into your duct work, and being it's in the attic and cold air sinks, it's going to downstairs.

I'd open the blower door on the furnace and look inside to see if you have a leak, good chance it's where the return duct connects to the furnace.

[donnae33]

The rivits in the vent tube that flows to the outside has detearieated. With a mirror & flash light able to see a small opening from where the rivits have came apart. It's somewhat like a chimney flute. The vent in the furnace that the air goes up and out through the ceiling/roof. How can I fix this without calling a repair man. Can not afford it. Unemployed from company closing. How can I get up to the area and will heat resistant tape seal it safe enough? Can I take parts apart safe enough to get to the opening to seal it. Need heat. am in Illinois and is getting cold. Hope someone can guide me.
It is a furnace in a mobile home (Trailer)

[airman.1994]

You ether have a hole in the duct or you have an insulation problem with the duct.