No pressure in 2nd floor tub

I have a new house construction project and I plumbed the house myself. My problem is that I have very little pressure coming out of the 2nd floor bathtub spout. I ran 3/4" water lines up from the crawl space. We are on city water. I do not have the hot water tank hooked up yet so I just have the cold water lines full. I did air test both the hot and cold lines and they both held 55 lbs of pressure for several days before I decided that there were no leaks. I installed a Moen Posi-Temp Pressure Balancing Valve. I appreciate any help I can get to diagnose the problem. Thanks,

Did you flush the system to remove any debris that might now be clogging the shower valve?

I only ran the outside hose faucets and nothing inside the house as I do not have any fixtures hooked up except for the upstairs tub. Should I drain the line and put a valve on the cold water line to the vanity to see if I have good pressure there?

Might be normal...the pressure balance spool valve in the fixture may limit the water if it doesn't see any pressure from the hot side. This is just a guess, wouldn't be the first time I was wrong.

Update. I drained the cold line tonight and put a valve on the cold line going to the vanity. I have plenty of pressure here. According to the replies to my original post it could be debris in the valve or the hot water heater not being hooked up. Any advice on how I should proceed? I haven't bought the water heater yet but will soon. For piece of mind, however, I'd like to clear this problem up. Should I try to investigate if there is indeed debris in the valve and if so, how do I do this? It is a Moen Positemp Valve. Thanks much.

I have seen pressure balancing valves colse all the way with the hot water off. Get the hot side going and then check it and let us know.