Why does my gauge go into the red/high pressure?

The most common reasons for the pressure gauge to indicate a red/high pressure reading are the car is not running, or the A/C is not on with the fan switch set to high and the temperature at its coldest setting. In order to obtain an accurate pressure reading the car must be running, the A/C set to the coldest position, and the fan setting set to high. Also, as the car’s compressor cycles on and off, the needle on the gauge will move in and out of the red/high pressure area of the gauge. This is normal. Here is an example of a car compressor cycling on and off: