Auto Temperature Control
Automatic Temperature Control, as its name implies, is an automatic climate control system, which automatically controls interior temperature based on the driver's demands and temperature information from various sources. ATC does this through direct interaction with the vehicle's A/C and heating systems. Some ATC systems have separate “zones”, where different temperatures can be maintained according to personal needs. ATC is usually an option, replacing manual heating and air conditioning controls.
ATC is largely a convenience option that keeps the interior temperature set to the driver's preference. ATC also provides some element of additional safety, since the driver needs to spend less time monitoring and setting temperature controls.
ATC directly controls the heating and A/C systems, so most problems thought to be ATC problems really lay in the systems it controls. Regardless of the symptom, have it diagnosed as soon as possible by a professional technician.