Did you short the low pressure switch? If not, you probably have to do that. Its the switch on the hard line on the passenger side, near the firewall. If you are standing directly in fron to the car, if you look at the first 'V' in Volvo on your valve cover, then look towards the firewall, that's your switch. You need to disconnect the connector and jumper across the contacts of the connector. When you are done charging, unjumper the connector and put it back on the switch.