Q. I maintain that it is more cost-efficient to keep the central air conditioning on at a high temperature (like 79 or 80 degrees) if I'm going away for a long weekend, than to turn it off and have to cool down a hot house when I return. Friends tell me this isn't true. Does any expert out there know the answer?

A. You are quite right to a point. It does take much more energy to cool a hot house then one that has been kept at a moderate temp. while not at home. However, some of the newer units are designed to cool more quickly using less energy, (SEER Rating). If your unit is 4 years old or older, you are on the right track. Keep the outside unit clean. Have the indoor coil and blower checked in the spring and change your filters on a regular basis and your unit will run at its greatest efficiency.

Q. My Mom owns a Trane air conditioning unit and has had nothing but problems with it. She had the coil replaced on it a couple of years ago. Now a technician is telling her that the coils are bad again. They are telling her that there is something in the environment, her sprinkler system (sulfur), which is causing it to go bad. Does this explanation sound feasible? She uses well water for her sprinkler system but has had this sprinkler system for nearly 20 years. Before she had to get a new unit about 3 years ago she never had problems with the coil. Is it possible that the air conditioning unit itself could be causing the coils to go bad? i.e, a Freon leak or something.

A. Absolutely NO. I am sorry to say that many people like to lie about stuff that you dont know about and EXTORT money from you.The refrigerant contains oil which moves through the system with the refrigerant and a leak in the coil is very rare unless hit with a lawnmower or such. Also a leak can be repaired but ther is no profit in it and it takes time.I am an HVACRR Tech, 15 years and have heqard it all. You are welcome to contact me and I would love to have the Tech. (supposed) explain it to me!!! I will give you my phone number to have him call.

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