ok since it has always done it, I still say you put the valve in wrong.
That is assuming you had gauges on it at somepoint and know it has a full charge.

The problem is the actual valve does not have enough stopping power so they have to put it in an odd place.

So
Engine --> heater core --> Valve --> to engine.

The valve has a direction printed on it.

normally you would think you could do
Engine --> valve --> Heater core --> engine

But if you did that, the valve can't hold back the pressure from the engine and hot water will start to flow into the heater core.
It will eventually get too hot for the a/c to overcome and you lose cooling.