gfretwell is correct.
Measure the voltage at the end of the run (pump) with the pump disconnected. If he has 240 or close I would bet the wire is way to small for the distance. The pressure switch or other controlling device should be located at the pump so I doubt he has problem there. But it's possible he is single phasing the pump, either with a bad conductor (not likely) or a bad controller ie: presure switch or starter.
He needs to do a voltage drop calculation, since it is in PVC it is not likely the conductors are damaged. No mention here in the post of any breaker trips either.
Can you imagine how he got that flat cable pulled that distance. He must have used his truck....lol He may have ruined the flat cable during the enormous pulling strain. Mabe a 90 or two? I hope not. Does he have any pull boxes. If so check all connections.
