During the air brake inspection, what should air pressure build-up be?

For a typical truck with a dual air brake system, air pressure should build from 50 psi to 90 psi within 3 minutes. Slow build-up suggests a compressor problem, a major leak, or other issues that need attention before driving. The exact specification varies by vehicle (some require build-up within 2 minutes, some allow more), but 50-to-90 in 3 minutes is the federal standard for most heavy vehicles. Check the test in your specific vehicle's documentation. Slow build-up means the compressor cannot keep up with normal brake demand, which is a serious safety problem on long descents or repeated stops.