CANT GET BRAKE SYSTEM TO BLEED OUT

[Dave SENIOR]

Hello I had replaced the Left rear caliper on my sons 1980 240 volvo 4 wh disk and when putting on new caliper an hook up brake line an try to bleed i get some lite pressure to come from the bleeder valve but then when I close the bleeder valve I can not get the cailper to work it will bleed but seems like week pressure the passenger side works fine good pressure and bleeds proper an caliper reacts to brake pedal being applyed,,, No reaction On the Left rear caliper???what Am I to do??any help any tricks Iam Not aware of???/