My attic gets very hot, even with 3 turbines. Although it is very hot
outside (temp about 99-102), an AC service man recently said that my attic
is still hot considering that all 3 turbines are working properly.

The house is mostly brick and I have vinyl siding over the wood (veneer?).

I'm wondering if the siding is preventing the attic from getting proper
outside air flow. The original outside vents were removed and covered when
siding was installed; the siding does have some venting holes.

How can you tell if the attic is getting proper ventilation??