BOAC you are correct in that he/she answered the original question.
No packs no pressurisation, full stop.
CJ driver.. from the Boeing 737 engineering training notes...abbreviated to a degree.
flt/gnd s/w to flt, OFV driven partially closed to take cabin to -189' .As aircraft taxis and takes off cab press is held at -189' .As airplane rotates the OFV is nearly closed.Ram air effect on the valve will not cause a pressure bump.(a sharp rise in cabin pressure).
I posted -387' in a prior post.My error. I did the course well over 20 years ago and memory failed but the principle is well remembered.
From the A320 eng course notes...
Cabin is pre pressurised as power is set for t/off to prevent pressure surge at rotation.
Note that both mention rotation not weight off wheels.The surge being prevented is from a change in attitude and ram air effects & airflow at the OFV.
bio161 further to the a320 question. as answered no pre press if no packs on but the 320 (older ones do anyway) have a ram air inlet purely for ventilation in the event of dual pack failure.operated by a s/w in the cockpit.Aircraft must descend to -10,000', when diff pressure is less than 1psi the OFV will open allowing ram air in to ventilate the cabin.