1992 Ford F-150 Bleeding the brake system

I had the passenger front brake line burst on me a few days ago. I went today and got a new a line and installed it. Everything went fairly easily. So, since it had never been done, decided to change the brake fluid at the same time. I have a manual vacuum brake bleeding system. One of those you connect and pump by hand. Started at the passenger rear and pumped until I saw nice clear fluid coming through. Same on driver rear. I'm now at the one where I replaced the line and I can get nothing to come through the bleeder screw. I took the screw all the way out and checked it to make sure the pathway was clear and it was. I've tried using the vacuum pump and the old 2-man bleeding method, but nothing so far. Just to check, I disconnected the line at the caliper and there is nice clear fluid coming out of there, so I believe fluid is getting to the line and I see no leaks.

Is it possible something is wrong with the caliper, which is preventing me from bleeding it? When I removed the bleeder screw a second time, just to make sure, it was completely dry at the bottom.