Can you over charge ac system?

Answer 1

Yes.

Each type of refrigerant has unique pressure/temperature properties. When cool enough or under enough pressure, a gas will condense into a liquid. The point at which this happens is given in a chart.

If my car is at ambient temperature (has not been running for a day or more), the pressures on the high side and low side of the system should have equalized and all parts of the a/c system should have equalized to the ambient temperature. For example, if it is 70F I would expect a fully charged r134a system to be pressurized up to (but not exceeding) 71.1psi as read on a gauge. Again, this is the highest pressure you could expect to see when reading the pressure of the high side as well as the low side. Any excess volume of gas will condense into liquid if you try to pressurize the system beyond 71.1psi at 70F.

A small amount of this liquid can be tolerated by your system. In a car, a part called the "accumulator" or "receiver/drier" can store excess refrigerant that has been forced to convert to liquid. When there is too much liquid refrigerant in the system, it can overwhelm certain components. Compressors in particular are not designed for compressing liquid. If you are lucky, your system may have either a blow-off valve to release excess pressure to the atmosphere or a high pressure sensor/switch to protect from excessive overcharging.

In a running system, the temperature and the pressure of the refrigerant are all over the place as the refrigerant is squeezed, cooled, allowed to expand, and warmed up. To complicate things further, in an automotive application as engine speed varies so to does the speed of the compressor. As the vehicle speed changes or the condenser fan runs, the refrigerant will decrease temperature to varying amounts. The outside temperature, the temperature inside the car (at the evaporator), and even humidity levels affect the efficiency of the system and affect the pressures that are present in the system. But "running pressures" rather than "static pressures" really give the only insight into how effectively the system is able to function. For this reason - It's best to have your a/c serviced by an experienced professional.