The original car came with factory air and heat. Like basically all ICE-cars, the warm air is done the excess heat from the combustion engine, and the cold air comes through a compressor. Two entirely separate circuits that only meet up in the air-handler box behind the dashboard.
Now that all of the original engine is gone, the entire heating / cooling setup is up for re-design.
The most common way of doing this in EV’s is to use an electric heater (a giant easy-bake box) to produce heat. It’s pretty inefficient when used at low air-speeds, and unless it is a really big box it can’t handle higher-speed air because it would overdraw the heating capacity of the electrical elements. The biggest thing I’ve seen out there is a 5 kW unit that’s used in Tesla model S and similar. That unit needs really good cabin air filtration to make sure no debris can get caught on the heater-coils else it’ll start catching fire and/or kill the performance of the heater.
In residential AC, it is very common to have a “heat-pump” mode. When it’s not too cold out, the AC system can be run in reverse and pump heat from outside into the interior of the house. It won’t work when it is really cold out (in the teens Fahrenheit or below), it takes a few more parts in the AC system, but it is much more efficient than the electrical heat.
Seeing as I’m in central Texas, I pretty much have to have the AC running, and it never gets too cold for a heat-pump. So, I’m being ambitious and am building out a heat-pump system. It has taken a while to figure out the size of the various components, but I think I’m ready to start construction.
The basic design follows this image (I found this via Google, I don’t know if it is for an actual car or just pretty pictures, and if someone has copyright please let me know and I’ll remove it):
The biggest AC compressor for electrical power that I can find is a 27cc unit from Benlinq. It came in at $600, it can run at 6000 rpm and gets me cooling that is comparable to 80% of the OEM system (using regular coolant).
To match that, math says that I need a 14″x24″ condenser and a fan that will push ~1,800-2,000 cfm. The original condenser is a little larger at 17″x26″ (and that matches the 80%<>100% between electrical compressor and OEM compressor), so I’ll try to re-use it. The space in the front section of the car is getting amazingly crowded by now, but I think it’ll fit and still squeeze out enough air-flow.
The original heater-box + fan had to come out to make room for the battery pack, and I’ll have to come up with an entirely new setup inside the front passenger fender-well. It should fit, but that part will be super-difficult just for outside air, and recirculating cabin air will be sheer magic. Working on it….