Working from memory on this one... I believe you will find that there are in fact two seperate pumps; one for the windshield and one for the rear. Chances are the pump is seized up from lack of use/corrosion. You can check this by first using a test lamp on the electrical connection for the rear pump (located below and in front of the washer fluid reservoir). Remove the connection and attach your test lamp lead while someone activates the washer switch. If you are handy/ambitious you can remove the pump and carefully open it up and repair it. I believe I have a procedure written up and stored in my Volvo folder- email me if you would care to have a copy (jrstarkie@att.net)

Randy