Volvo: Door Lock not locking, volvo s70, air pressure

Question
Dear Jason,

I have a 98 Volvo S70 and I noticed that my passenger door does
not lock anymore. The button goes down but the door doesn't
lock.  Someone told me that it is an air pressure lock and that it
needs to be replaced.  Does that sound like what it is?  If so, is
that something that is hard to replace?  Could I do it myself?  
Where do I find the part number in order to buy a new or used
one?  Any help would be greatly appreciated.

Thanks,
Anthony

Answer
I don't know what kind of lock is in the door for a model that new, but I suspect that if you can get the door panel off, you'll be able to tell pretty easily what is malfunctioning, then probably order a replacement part from Volvo.  With enough patience, this is probably a do it yourself job.