The first engines, the A10 & then the 1200 [up to the end of 1973] had the disrtibutor right up front over the oil pump.

It would have been decided at a corporate level that with the improvement in aircon compressor technology & with the public's increasing apetite for airconditioned cars, that this would become a feature of the new models. Problem was that with the old engines, there really was no place to mount it.

The alternator was moved from low on the left to a position high on the right & this cleared a position for the compressor. The left engine mount was moved back 40mm to also provide more room in this area.

With the alternator now located over the distributor it was necessary to move it back to utilise the old fuel pump eccentric as the new distributor drive gear. The engine mount was also moved back 40mm to be equal with the one on the other side. A new position was found for the fuel pump & the job was done.

If you look at the newer type blocks you will see the cast & machined mounting points for the aircon compressor mountwhere the alternator previously resided.

In the smaller cars aircon did not prove to be as popular as first thought, but the block was 'aircon ready' & that's the way it stayed.

The distributors are interchangeable, but only if the steel mounting plate at the base stays with the block & is swaped onto the next distributor. The later cam can be used in the early block easily enough, but the fuel pump hole must be blocked off as there is a gear in that location & the pump won't run on it.
The earlier 1200 head will work without mods on the later block, but the later head needs to be slightly modified for the different method of geting oil from the block to the head for the rockers.

Wow, thanks for the info. That the human thirst for convenience could change the design of an engine. Though I can't imagine having to drive an A12 engined car with aircon pump running at any kind of acceptable speed. You might get away with the newer type pumps though, they have become far more efficient and less power sapping...

Here's some quick rule of thumb:
* No A14 has the distributor at the front
* A14 blocks have "A14" stamped on the ID plate

And an A12 with original Air Conditioning can do 110 kph no problem.

Will this rulle of thumb count for the A15 engines as well?

How effective were those aircons? Did they have different heater/fanboxes than a standard 1200 to accomodate the inside "radiator" of the aircon system.

Since the A12A, A13 [both kinds] A14 & A15 were all made from 1974 onwards, the basic 'rule of thumb' will apply.
All were of the newer block design, so all had rear distributors & all had the basic engine designation stamped as a prefix to the engine number.

Only the A10 & 1200 engines [up to 1973] had the front distributor.

The first model that I know of to get 'integrated' aircon was the B310, so the earlier models got some sort of under dash unit.
Factory Air [Kit, Cooler, Room- dash] was available in some markets for both the B10/Datsun100 as well as the B110/Datsun 1200 but these seem to have used the bulky & power hungry twin cylinder York compressors mounted on cumbersome bracketry. It was not really a pretty sight under the bonnet.

Aftermarket aircon was also available, even through dealers in your new 1000, 1200 & 120Y & these all were of the same under dash type.