R134AManometer for quick measurement of the filling quantity.
The pressure gauge is simply plugged into the low pressure side while the air conditioner is running and you can tell whether the air conditioner is working or not and whether the low pressure is in the green range. The colored areas make it easier to recognize.
Simply attach the pressure gauge to the low pressure port of the running air conditioner and read the pressure. A running car air conditioner has a low pressure of about 2 bar. If the pressure remains 0 bar or much higher, the air conditioning has no function.
An exact diagnosis is only possible with high and low pressure, eg M2W