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.
We suggested that the external flash be set to the TTL mode. The TTL (i.e. , T hrough T he L ens) mode means that the camera will measure the output of external flash and stop the flash once illumination is sufficient.This is the easiest mode of using external flashes.However, do keep in mind that the Coolpix 990 is not true TTL cameras in terms of flash control. It measures flash illumination with a flash sensor next to the on-camera lens as shown below. As a result, what this sensor sees is usually not what the lens sees.his is the easiest mode of using external flashes. However, do keep in mind that the Coolpix 990 is not true TTL cameras in terms of flash control. It measures flash illumination with a flash sensor next to the on-camera lens as shown below.