No air blowing out of the vents in my house! Is my HVAC unit hosed?

September 24, 2008 8:42 AM

My heat pump / air conditioning unit (HVAC?) is not blowing in my house. I have a programmable thermostat. When I walked past it this morning it said 80 degrees. I bumped it down a couple of degrees and waited to see if it would kick on. No such luck. The unit outside ( the condenser I think.... large box with a fan on top) did turn on but nothing is coming out of the vents. Anyone have any idea what could be wrong? I am getting ready to have to spend some serious money on a replacement? Thanks!
posted by pleuroma to home & garden (7 comments total)

You have a circulator fan that isn't running from the sound of things. It should be at the air handler. I would check for blown fuses/circiuts at the panel and maybe that the air handler.
Do you have a service contract? If the fan is toast you will need it replaced and most likely will want that done by an HVAC company.
posted by a3matrix at 8:52 AM on September 24, 2008

We have the same problem. Here's how we deal with it:

There is a small overflow pan and a floater switch on the inside part of the unit. (Ours is in the attic.) The pan is for condensation (I think) and when it's full, the floater switch shuts off the blower. For whatever reason, our blower shuts off even when the pan is bone dry. But if we trip the switch (lift it and drop it again), the blower will come back on.

We do this every day or two. It's a pain in the ass, and it's not a fix, but it's free, at least.
posted by cereselle at 9:04 AM on September 24, 2008

a3 matrix is 100% correct. Depending on your zones say you have a 3 story home, it could be quite expensive. Your going to need to contact an HVAC company as soon as you can. I assume this may also be an issue with your heat come this winter...
posted by TeachTheDead at 9:21 AM on September 24, 2008

Programmable thermostats are notoriously unreliable, if yours has a fan only setting it could be the stat. Temporary replacement with a cheap manual stat could test for this and the stat is a good thing to have on hand when your programmable fails Xmas/New Years eve.
posted by Mitheral at 9:36 AM on September 24, 2008

Do you have gas heat? Check the gas emergency shutoff switch and make sure it's on. Ours is located on our basement stairwell, and although it's big and RED, people are always turning it off by mistake. It causes the exact symptoms you describe.
posted by drinkcoffee at 10:35 AM on September 24, 2008

Had the same problem when I went to turn on our unit in June. Isolated the problem to the air handler in the attic and figured the small circuit board was the problem. Called the HVAC company that installed it and paid $100 for a service call to have the serviceman tell me what I already knew - the small circuit board was the problem. Waited 3 days for the manager to call me back and tell me I'd better sit down - the part had to be ordered and would cost ~$700 to get and install.

I went up again myself and found the part number and found it on the internet for $300. I also had a electrician friend try to source the same part via the large electrical contractor company he works for. It had to be ordered, but he got it for me in 2 days. We went into the attic, installed the new part in 5 minutes, and - presto - we were cool in minutes.

The cost for the part? $24. Is it the small HVAC company that tried to screw me because he can? Was it the manufacturer (large, well-known AC equipment maker) trying to screw me because they can? I don't know, but if a "professional" tells you that you need a $$$ part, don't be afraid to do your own research. Ask for the part number and look for other sources. And ask yourself if it's reasonable - a 3" x 4" circuit board should not be $700. Good luck.
posted by Wilberto at 11:24 AM on September 24, 2008

We had the same problem when we turned the system on at the beginning of the season -- and it happened occasionally in the summer before, but always seemed to correct itself.
As well as a fan problem, this could be a coolant level problem (which was our problem, with the same symptoms). To isolate the problem, open the door to the attic or basement, where the HVAC unit is and see if the fan noise starts or stops when you turn the temp up or down radically - by about 10 degrees. If you hear the fan kick in, it is likely to be a coolant leak (easily fixable, for a callout charge + 3-4 liters of coolant).
If you do not hear the fan turn on and off, it is likely a fan replacement (again, easily fixable, but may cost a bit more).
Many AC maintenance companies will come out and diagnose your problem for a low charge. I would consider asking your neighbors if they have a reputable AC company that they would recommend.
posted by Susurration at 11:43 AM on September 24, 2008