I have a 70 Challenger that is a non-A/C car. I have an A/C dash and would like to get and install the factory under dash unit.
I will use a Sanden compressor and aftermarket evaporator but I want to keep the factory vent and heater controls. So, forward of the firewall is aftermarket, behind is factory.

Don't want to use and aftermarket dash unit because you lose the vents; also, some of their controls are kludgy.
And, the Classic and Vintage units only circulate air inside the car. They have no provision for taking in outside air.

Has anyone modified their firewall to install a factory A/C unit?
My first thought is that it would be easiest to weld patches on the non-A/C firewall openings and then cut the appropriate openings for the A/C box.
Other option is buying an AMD A/C firewall and sectioning the passenger's side in. This seems like way to much work. Plus it's a lot of money.

Anyone done this? What methods did you use/find best?

Thanks,
Robert

My convertible Challenger has had AC added to it. They just hacked a bigger hole in the firewall for the AC stuff.

I did the opposite. I converted an A/C car to a non-A/C car, but the work is the same.

I had previously parted out another car, so my task was easy. Cut out a section of the A/C firewall to match the cleaned up section of the non-A/C firewall from the parted out car. Weld the firewall piece into place. The same thing could be done with an AMD A/C firewall section.

From there it was just the matter of a little cleanup bodywork and then change all the under-dash components from A/C to non-A/C.

Recommendation: Find a complete system from one car so you don't have to piece one together!!! Take lots of pics and notes before removing the system and while performing the removal. The A/C stuff is a lot more complex under the dash (vacuum hose routing, etc.)!

I went with all the OEM under-hood components (to look stock). I actually was able to clean up the passenger side of the engine compartment a lot getting rid of the A/C stuff.

For you, going with aftermarket stuff under the hood would be just as easy as with the stock stuff.

You'll also need to find the right control switch and panel, depending on whether you have a rallye dash or not, as the switch panels are different for each dash.

Also, I found it a lot easier for locating the blower motor, heater hose and heater box mounting holes by transferring it all over in one piece of the firewall, rather than trying to patch in/cut new the holes separately.

Plus, the opening for the A/C blower motor has a raised lip and is in a different location than the non-A/C blower motor, so that would need to be added separately (to look stock). Doing it all in one shot made locating the components in the correct spot much easier.

And factory A/C cars had different diameter fan/water pump pulleys, fan clutches, and different water pump impellers than non-A/C cars, mainly to take care of extra cooling needed at idle and low speeds.

Is it possible to install an A/C dash, use a vintage A/C box and connect the outlets from the A/C box to the dash vents with hoses as used by OEM?

sure. why not ? you may need to make an adapter ring for the under dash box vent holes if those holes do not match the OEM connecting hose size.