Defrost?
 

I've pulled my dash off and I'm eliminating all the brackets,ducts and wire that I can. Next is the AC/Heat unit. I plan on leaving the heater core for now. Looking at other cars online it appears some have a defrost button installed. In Michigan that would be nice on a cool spring and fall morning. Unfortunately is looks like the AC unit provides the fan to blow over the heater core and get the defrost so if I remove the AC unit no defrost. Am I correct in that assumption?

Provost motorsport has a custom defrost listed on one of their cars for sale. How hard is that to accomplish something like that? Is it just fan that blows over the heater core toward the windshied . . . instant defrost!

If you've got pictures post'em please.

Defrost uses the ac to take away moisture at the same time it uses the heater core to blow warm air. If you take away the ac compressor then you will lose the moisture removal part, but if you leave the heater core you will still get warm air. It won't defrost as well without the ac part.

Thanks Tommy. Compressor getting deleted. Here is a hypothetical . . . running on a 60 degree morning, windows open, car is cold, full suit and helmet. Will the windshield 'fog' up? IF there is no AC compressor, is defrost just slow or totally nonfunctional?

I suspect that to get down to race weight you will need get rid of everything under the dash. The HVAC unit is somewhat heavy. As Tommy said, once you delete A/C there is little value to "defrost" airflow. My recommendation is to get rid of A/C, all of the maze and bulk of HVAC stuff in the dash, the heater core and heater pipes under the car, etc. You will also be able to get rid of the HVAC head unit.

Fogging can be problem without defrost, if it's raining or humidity is just so. I've only experienced it during rain. Solutions include:
- Fog-X
- rigging up a small electric fan on top of the dash, to blow on the windshield
- routing a fresh air intake vent (thru the existing firewall air port, and to the windshield dash vents?)
- a short stick with a towel, to grab for wiping fog off the inside windshield while racing (not joking, I have seen it)

(I have no solution on my SPB car!)