We have one AC unit (roughly 1 year old) connected to two zones: Zone 1 is upstairs and Zone 2 is downstairs.

Yesterday, our AC seemed to completely stop working for the upstairs but continue to work well for the downstairs. Not being very familiar with this topic my wife and I began some common-sense troubleshooting to see if we couldn't gather up some helpful information for relaying to a technician before they make a trip out. Perhaps we could get some further information here as well.

The upstairs is Zone 1, and when it's on it registers as being on in the panel in the Attic. No flashing lights for any zones at any time suggesting a short-circuit. When we turn on the air from the thermostat upstairs, it registers at the panel and kicks on the AC unit. The same is said for the downstairs, which works fine.

In the attic we did find that the last part of our unit, a giant silver box where the air leaves the unit (sorry for the highly-technical terminology, hehe) had some foil tape that was coming loose due to condensation - this created a rather large gap that allowed a lot of cold air to escape into the attic. We pressed this tightly, but found no improvement in the airflow upstairs.

So the facts are simple, the unit works. It blows air to the downstairs with appropriate force and at the expected temperature. It does not blow air upstairs although there is one vent in particular that you feel as though you might have some cold air dropping out of...it's one of those things where you wave your hand next to it for about a minute saying, "Wait, I think I feel something...".

The Panel works upstairs, no shorted circuits. There was a visible gap in the taping but pressing this closed doesn't appear to fix the problem. No other noticeable gaps or sounds of air escaping.

All I can wonder now is if there is a fan that pushes air to the upstairs vents and a fan that pushes air to the downstairs vents. If so, the fan to the upstairs may have lost power or been prevented in some other way.

Given this information, and the fact that AC units are apparently very popular with home-owners, is there anything I'm not considering or something I should double-check before I pay a technician to come into my home?

Here's a rough-sketch of what our unit in the attic looks like:

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Our air-intake works just fine upstairs. The filter isn't old and prevents no air-flow. The panel is working just fine, and the box prior to the Air Out is full of cold air that was being back-blown through a gap in the foil tape onto the box left of that area. Fixing the gap doesn't seem to have remedied out problem.

1 Answer 1


Generally, there are not 2 fans. Instead, there are electrically controlled dampers that open and close based on signals from a control unit. The damper for your upstairs vents is probably jammed.

The control unit for the dampers is usually mounted on the wall near the air handler, or directly on the air handler. There should be 4 to 6 wires coming out of the controller: one for each thermostat, one for each damper, and possibly one or two more going to a power supply or to the air handler. They're probably labeled if you open the cover. Follow the cables to find the dampers.

The dampers that I have in my house have a cover that you can pop off to get at the damper and move it by hand.

  • The damper wire in my image above goes from the control panel to the exhaust. It's fed into the vertical release channel through the thick insulated exterior. I'm not sure how I'll be able to gain access inside to see if the damper itself is jammed without removing the exterior, and I don't see any simple way of doing that. Perhaps, at this point, I need to call a professional?
    – Sampson
    Commented May 25, 2011 at 14:11
  • are those things you have labeled "air out" just regular looking insulated air ducts? if so, you can just cut them open and seal them back up with tape or a mating connector from a hardware store.
    – longneck
    Commented May 31, 2011 at 17:26
  • I'm not sure exactly - they have zip-ties at the base, as though they were tightened to hold on to something.
    – Sampson
    Commented May 31, 2011 at 18:30
  • well, there you go! go get some extra-long zip-ties from your local home improvement store. then you can cut the zip-ties that are on there, investigate the damper, then zip-tie the duct back on.
    – longneck
    Commented Jun 1, 2011 at 12:50
  • I may give that a short - the ducts are also stuck to the airbox with some type of putty at the seem. May need to cut through that and reapply more afterwards.
    – Sampson
    Commented Jun 1, 2011 at 17:56

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