On Wednesday, May 16, 2018 at 12:46:28 PM UTC-4, Sonny wrote:
On Tuesday, May 15, 2018 at 8:07:41 PM UTC-5, DerbyDad03 wrote:

Am I expecting too much from this rig?

I would try increasing the air pressure to the max your gun is recommended for.

On this video - https://www.youtube.com/watch?v=k6L_ArXCbYs - I wasn't too impressed with the speed of the paint removal (one coat of already maybe loosen paint?). I would think any surface, with a primer, would be even slower to blast. I might suspect the primer coat on your vents have been baked on, at the factory, making that coating harder to remove, using the walnut grit, if you're wanting to remove the primer, also.

Test with a bit of fine sand. With that delicate of small gun set-up and pressure regulation, controlling the more aggressive sand might be easy enough, hence not damage your vents' metal.

Sonny

Yeah, I watched that video last night. He was the one that said 50 PSI was
enough. No way.

I up-ed it to 90 PSI earlier this evening. That's max for the cheap HF gun.
It worked a little better, but the problem is that my 150 PSI 6 gallon
compressor ends up way below 90 PSI before the 20 oz bottle is half empty.

In any case, I got the job done. What I ended up doing was stripping all of
flat surfaces with liquid stripper. I then used the stripper and a toothbrush/
steel wool to get as much paint out from between the fins as possible. It was
impossible to get it all, so next I combined the stripper and the sandblaster.

I slathered stripper between the fins, let it work for a few minutes and then
blasted it and the loose paint away. I'd say I got more than 99% of the paint
off which is enough. I've already primed the vents and hope to get the first
coat of paint on tonight.