1 CostHelper readers report costs of $1,000-$3,700 for major air conditioning repairs, with an average of $1,829. 2  Installing air conditioning in a vehicle that doesn't have any can cost $1,500-$4,000 or more, depending on location and the vehicle's year, make and model; luxury vehicles can cost even more. This generally includes replacing a few parts like hoses, sensors, or either the compressor or condenser. 2  CostHelper readers report paying $171-$727 for minor air conditioning repairs, at an average cost of $488.
TTL stands for Through The Lens, and in the case of SLR metering, it indicates how the light is measured--that it's the light coming through the taking lens, rather than, say, an exterior sensor.
A-TTL is an initialism that stands for Advanced-Through The Lens flash metering. As with ordinary TTL flash exposure systems, a sensor inside the camera reads the amount of light being reflected off the film during the exposure. When the sensor determines that the exposure is sufficient, it terminates the flash pulse. A-TTL, first seen on the T90 (which predates the EOS family), is a flash exposure system that adds a brief preflash during exposure metering when the camera is in the programmed exposure (P) mode.