Firstfives.org

Playing around on my 1976 car, I found the heater remained on when I turned the a/c on. It switched from the fresh air fan (firewall) to the console a/c fan, but the heater was still working. This surprised me because I thought turning the a/c on would cancel the heater completely. This is an e12 with the separate factory a/c controls.

I did then turn the heater off when making this discovery.

Let the AC and Heater battle it out.

canada karl wrote: Sun Apr 24, 2022 12:05 pm Let the AC and Heater battle it out.

Ha, ha, it did for about 5-10 minutes Seriously though it created stratified heating, warm at lower levels and cool above.

I can't believe I am still getting surprised by these cars, lol. I still don't think I completely understand the car's heating and ventilation.

Yeah that does seem strange they would both be working at the same time. Make you wonder, is it suppose to do that?

maybeillbuyit wrote: Mon Apr 25, 2022 10:01 am Yeah that does seem strange they would both be working at the same time. Make you wonder, is it suppose to do that?

I guess it's because it's such an early car. It does cancel the heater/fresh air fan when you turn the a/c on, so I suppose it's working correctly. I haven't modified anything in this area. I just decided to experiment and was surprised when the heater stayed on (with the heating fully to the footwells).

I know there is a wiring diagram for early cars with a/c, which is in the BMW handbook and repeated in the Haynes manual. I suppose that would explain it.

I know the handbook says you must use the fan when the heater is on (to get rid of the heater core's heat). Of course that is from the European handbook which is assuming you don't have a/c. In my handbook it makes no mention of a/c, except a one liner in the back saying you could have a/c as an option, and it's also covered when showing the fuse box fuses.

Okay, ancient post, but I hate to leave such a thing hanging...

The A/C is also effective as a dehumidifier; defrost is WAY more effective with A/C on. Unless you're talking about expecting it to allow A/C when defrost is selected but not other outlet locations? In cars that have it, I generally prefer to run A/C all the wet season to help keep the interior dried out. I've never had a car incapable of making things plenty toasty with the A/C running.

I've only just gotten my E12, and have only had even older (2002 w/o AC) and newer (E28, E39, MINI) BMWs 'til now. And mine needs a bit more poking at before I'll be worrying about when the A/C should be running... Okay, back to searching the forum to see if I can find out what the distinction is between the two different Haynes E12 manuals...