yesterday I tested a Auto AC which we are developing for a new vehicle. We are using R134a refrigerant. When the system was tested in windtunnel for different operating conditions, it was observed that the discharge pressure was showing a cycle of 3 bar pressure difference every 3 minutes. for example 18 bar for 3 min and 21 bar for the next 3 minutes and so on.

There was no compressor tripping during this phase. I am not able to get the reason for this kind of phenomenon. I have not observed this kind of phenomenon before in any vehicle nor have my colleagues.

Surprisingly this phenomenon was not observed during vehicle idling condition and also as the vehicle speed increases the cycle time came down.

Can anyone throw some light on this.