87 190E

A/C will not engage, I have no power to the pressure switch (correct me if im wrong) I thought it got the signal from the push button control. As earlier suggested I grounded the pressure switch circuit- No change. I am not sure were to go from here, any ideas much appreciated.

Also as I read in the manual, the self diagnostics as indicated by time between the fan turning on and going off, do you need to have the just the ignition on or the car running. With the car running the fan stays running, when just the ignition on it cycles at 30 secs. feedback potentiometer?