Your car is 1.4 so it should use the CFC328 dualogic unit. I think the non return valve is located blue line. (The valve is usually located near the accumulator) In Brazil they sell the valve.

Thanks for that Tonico ! Would you mind to share dualogic dedicated manual (if any) ? U can contact me by PM ...

BTW, what do you think of my disgnostic ?

BRs, Bernie

I think your diagnostic is correct. If it is the one way valve then it could simple be the o rings in the valve that are bad, or the spring the is broken or stuck. Also the filter in these valves sometimes gets blocked.