Quote Originally Posted by bulldogcountry1 View Post
I built the car. It has a Hot Rod Air system in it. I don't see any evidence of a leak anywhere. Would it be inside the evaporator? If so, that's going to be a pain to get to.

Could it possibly be a leak in the AC system. I know I have a leak there because it will only blow cold for a couple weeks at a time. I didn't know if leaking freon could cause a white dust.
Quote Originally Posted by rspears View Post
I think Barb's right here, and you probably have a very small heater core leak, not enough to drip but getting things wet inside the duct. When it dries the chemicals in the anti-freeze and maybe mineral in the water are left behind, and dry to a dusty deposit.
The AC is just freon gas with an initial charge of compressor oil, and freon doesn't leave any type of residue other than frost from the air if discharged quickly. I stand by my previous answer - I think you've got a tiny, pinhole heater core leak. Call Hot Rod Air and ask their tech guys - I bet it won't be the first time they've been asked.