Dear Jim: Although it’s noisy, my 12-year-old central air conditioner still runs. With electric rates going up, rolling blackouts and global warming, I should probably replace it. What is the best model for 2001? – Char Z.

Dear Char: In addition to your excellent reasons for replacing your old air conditioner, vastly improved comfort is also a reason why many people make the change. The newest models for 2001, especially two-stage models, are quiet and hold room temperature very steady with improved humidity control.

If your central air conditioner is 12 years old, it probably has a SEER (seasonal energy efficiency ratio) of about 8. The newest, most efficient models have SEERs from 16 to 18. Installing one of these would cut the electricity usage by half or more. If everybody replaced their old units with new ones, there would be no need for rolling blackouts this summer.

Air conditioners that use new earth-friendly R410A refrigerant, instead of ozone-damaging Freon, are becoming much more popular. In fact, Freon-type air conditioners will be phased out of production within 10 years by law. R410A models are beefier for better reliability and quieter operation.

If you are interested in getting the very best central air conditioner for your home, select one of the new two-stage models. These models have a low-cooling level for normal weather and a high-cooling level for extremely hot weather. In effect, it fine-tunes the cooling output to your home’s needs.

The newest, most efficient and least complicated design is a two-stage reversing R410A compressor. In the low-output stage, the compressor rotates in one direction, which operates only one of two pistons. In high output, the rotation reverses to operate both pistons to double the cooling output.

Any of the two-stage models offer many advantages over a single-stage model. Since they only operate on high level during the hottest weather, they do not switch on an off as often during normal weather. This keeps the air circulating, reduces noisy startups and dehumidifies better.

Although your old indoor blower can be used with a two-stage model, it is best to install a new one with a variable-speed motor. These special blowers use 75 percent less electricity than your old one. The “smart” motors have a soft-start feature to reduce noise and drafts when they start. This also allows a thermidistat to be used to precisely control humidity.

If you choose a single-stage model for its lower initial cost, select one with a scroll compressor (preferably R410A instead of Freon). Scroll compressors use a simple, reliable design and are quiet. Installing a new variable-speed blower with it can increase the SEER to 14 or higher.

Write for (instantly download – www.dulley.com) Update Bulletin No. 814 – buyer’s guide of the 14 most efficient one- and two-stage central air conditioners listing cooling outputs, SEERs, comfort features, warranties and a savings chart. Include $3 and a business-size SASE. Send to James Dulley, 6906 Royalgreen Drive, Cincinnati, OH 45244.