A lot of pressure - at times in excess of 150psi. As I stated before it is illegal to discharge freon into the atmosphere and can be dangerous. When the system is discharged the entire system will then need to be evacuated and re-charged with freon. Unless you have the proper equipment you will need to have this professionally done. I have three W123 cars (sedan, coupe and wagon) and after the under dash panel is removed on the passenger side it normally takes about 5 minutes to remove the blower from the housing.