Q. We have been having terrible problems with our central air conditioning unit. Our house is about 8 years old and we have a zone system (separate heating and cooling thermostats for upstairs and downstairs). For the past 2 years the unit is not cooling the house properly (heating works fine). We had the dampers replaced 2 years ago and I know the dampers are fine. We have had several repair technicians look at the unit. They always recharge the unit with more Freon (3 times in 1 summer) after claiming to fix a leak. This past weekend again a repair person claimed that we had an internal leak in the unit. He said that he had plugged the leak and then he charged the unit with Freon. Not only did this not work (our house continued to get hotter from 73F to 85F while AC was running all day) the pipe coming from the unit outside our house was all frozen over with ice (all the way to where the insulation started). Any suggestions or help will be appreciated. Thank you.

A. A system only needs to be charged once, when it is installed. If it gets a leak, the leak must be repaired, and verified that it is repaired with a vacuum test. It is a laborious process, and some homeowners would rather just juice up the machine each year than spend the funds to get it repaired. Some units have leaks that can never be identified. There are lots of fittings, small bends in the coils, and hundreds of feet of tubing that need to be traced with an accurate tool. Many Tech's don't have access to this tool, and rely on soap bubbles to identify leaks. Contact the manufacturer of your unit, and have them recommend a competent company in your area. If it is the company that you've been using, explain that they have not fixed the unit. For very hard to find leaks, there is a product available that can be added to the refrigerant similar to "Stop Leak" for your auto radiator. This product is rather spendy, about the same price as five pounds of refrigerant, but if you are charging your unit each season, it would be worth the investment. Contact the company that "repaired" the leak last time, and ask how the technician verified that the leak was repaired, and how he verified that the charge was correct.

Q. We are trying to fix the air conditioning at work (the landlord won't do anything) and need to replace some parts. We have the ducts and I have found out that the ducts are connected to the collars (male/female). The collars are then attached to a big square piece which then has the grille attached where the air goes out. Does anyone know what the big metal square piece is called? I've been looking online but so far, no luck. And if you know of any good diagrams illustrating this, that'd be great as well. Thanks!

A. You are referring to a supply air plenum. And the grill piece is called a supply register.

Q. I think my AC unit is shot. I suspect the repair to be major, so cost is pretty important to me. Can anyone recommend a dependable repairman or repair service that won't gouge me? Thanks!!

A. Independent HVAC steve baser 214-724-1862

Q. Does anyone know a good website that teach me step by step how to service ( and do commonly needed replacement) my single room (Window /wall mounted) Air Conditioner. Googled website almost all only show companys that do air cond repair. I want this as new hobby ! T H A N K S !!

A. Try starting here: http://www.hometips.com/cs-protected/guides/centairfix.html Google diy air conditioner repair. gl

Q. I just moved into a new home that had never had the ducts cleaned. The house is a ranch with gas forced air heat on one zone with about 9 vents. I found this company on a coupon for $45 which included unlimited vents and a couple access holes. When the company began their work they found mold and the price skyrocketed from $45 to $1400. Does this sound like a screw job or is that price accurate for mold removal and duct cleaning?

A. Mold removal/remediation is entirely different from air duct cleaning. However, it is not uncommon to find mold in your air ducts. That is why we recommend the Electro Breeze Duct Mount UV kit at http://www.allergy-relief-air-purifier.com/air-conditioning-filters.html. This unit will eliminate mold and bacteria from your indoor air and keep your air conditioning coils clean from mold. You must consider that to remove the mold from your air ducts, the air duct cleaning company is entering into a potentially dangerous situation for their employees. This requires expensive equipment and a person with the skills to do the remediation properly. Now that they have knocked the mold loose, you will need the high efficiency filtration and ultra-violet light of the Electro Breeze DMUV kit to kill and capture the mold spores in your indoor air. I hope this helps.

Q. My car is getting older and I've noticed the air coming from the air conditioning ducts and air vents smells musty, dusty, and dirty. Is there a way I can clean the ducts and vents? Also, is this something I can get done at an auto detailer?

A. The answer to your 2nd question first. Maybe?! Some detailers will only clean/restore what they can reach, although there are some who might go the extra mile. The problem is, they don't want to be responsible for destroying your dash vents to get at the ducts. When I worked in a body shop, we simply used compressed air through the vents to blow out the dust and dirt accumulated while the car sat inside being worked on.......some people even put pieces of air freshner directly in the vents to sweeten the smell afterwards.

Q. My doctor told me I need to get my air duct cleaned, but I keep hearing all kinds of horror stories about air duct cleaners. Does anyone knows of a good air duct cleaner near San Francisco?

A. Here are some Union companies that do duct cleaning. They all do good work. Atlas Heating and AC Oakland, CA 510-893-1343 Advanced Solutions Heating and Air Conditioning San Mateo, CA 650-347-4828 Bell Products Napa, CA 707-255-1811

Q. I have central air in my apartment and for the most part it works but lately it has not been cooling down the apartment. Any ideas on how I can fix this? Thank you.

A. How old is the unit and when was the last time it had a freon charge? Unless it has leaks, the ac unit should be checked and recharged once a year. If everything is working, but it is not really putting out cold air, usually an indication of a recharge needed. To verify everything is working: Set the thermostat to Auto, Cool and about 75 degrees. If air is coming out of the vents, the air handler (inside unit) is working ok. Next, go to the outside unit and see if the fan is turning and the compressor is running. (fan by sight; compressor by sound). If okay, all components are working as they should and the unit probably needs a recharging.