Many H.V.A.C contractors are turning to telephone “on-hold” advertising as an effective, inexpensive way to market products and services to a captive audience. Listeners on the other end of the line will hear about spring cleaning-and-check specials, financing on a new air conditioning system, or air cleaners to help them with their allergies. —John R. Hall, “Commercials on hold are music to the ears of H.V.A.C.R. contractors,” Air Conditioning, Heating & Refrigeration News