Home A/C question.

August 14, 2007 9:57 PM

Hi I live in Houston,Tx. August is our hottest month, and my home ac unit is acting up. It seems that the filter never gets dirty. I doubt that the ac unit is sucking return air from my house. Please help!
posted by Noodles to home & garden (3 comments total)

The direction of air flow through a window air conditioner is generally controlled by a set of louvers that mechanically open or close to allow outside air to be pulled in by the circulating blower fan (often a squirrel cage type blower), or not. Sometimes, the mechanical linkages for opening and closing the louvers become too stiff to operate, due to corrosion caused by the condensation of water remove from the air. Other times, the switch that selects recirculation or "fresh air" as the air source is broken, so that the soleniod that moves the air control louvers never changes position. In a window unit, it's usually a simple matter to remove the cover, and see what is happening, directly. Lubricate mechanical fittings and linkages with light grease, or replace bad switches/position sensors, as appropriate.

In central air systems, the potential for problems is a little greater, depending on where and how the system has been integrated with the heating functions, and how the air source selection is performed. Many central systems will automatically pull air from outside, if not explicitly set for recirculation, at the thermostat, and again, seasonally, at the duct work for intake air for the furnace. Look over your thermostat control carefully, and be sure your settings are appropriate. Then, look through your ductwork for controls that cut off outside air during air conditioning season, and put them in the proper summer operating position. Don't forget to change them back when winter heating season arrives.
posted by paulsc at 10:50 PM on August 14, 2007

It's houston so it's almost certainly central A/C.

When your air is audibly on, can you feel any movement of air going into the return vent? How about if you remove the vent? It should be noticable.

I'm not an expert but if you have clean filters and an impeded air flow, the most likely problem is that your AC coils in the unit in the attic are either dirty, or freezing over. Either case doesn't let air through the unit. You can usually diagnose freezing by checking the drain pan... you might need to turn off the AC for a while, and see if a lot of water stars accumulating there. Cleaning the coils might help, you can do it yourself but it's a pain in the ass and you might damage them (there are tons of fins that can be bent)

Having someone come do an inspection of your A/C to give you an estimate is probably free. Hearing the $$ it'll cost to repair it might not be so nice though.
posted by RustyBrooks at 8:35 AM on August 15, 2007

I kind of doubt that A/C units in texas are ever set to circulate air from outside. It's just too damn hot here.
posted by RustyBrooks at 8:36 AM on August 15, 2007