280ZX, 310, 810

Remove valve. Draw air through port "A" of valve. See Fig 1. Apply at least 1.46 in. Hg. A constant air flow should be felt. No air should be felt below this point.
Draw air through port "B" of valve. Apply at least 0.59 in. Hg. A constant air flow should be felt. No air should be felt below this point.
Continue drawing air through port "B" and seal port "A" with finger. Apply at least 1.38 in. Hg. A constant air flow should be felt. No air flow should be felt below this point. If valve does not test as indicated, replace valve.

Fig 1: Check Valve With Vacuum Relief Valve (280ZX, 310 & 810)
Courtesy of NISSAN NORTH AMERICA, INC.