[liuleichan]

>so everyone has to have their units recharged every year?

Not necessarily.

But they will need their AC recharging when the level of refrigerant is low enough to affect the compressor working effectively.

>The system is sealed the same a home unit except for the
>drive on the pump.

It is not used / operate in the same way as a fridge, and it's not subject to the same adverse conditions.

>Therefore if the seal is ok it should'nt leak.

In an ideal world, it shouldn't.

Yet they do - quite frequently.

And leaks can be quite difficult to trace, even with dye and UV lighting. And when they are found, they can be rather minor - yet probably quite expensive to put right.

You can bombastically claim it's just like a fridge, therefore it shouldn't leak - but they do, and you'd be wrong - it's not *just* like a fridge, and it's not used just like a fridge, and it's not able to operate in quite the ideal circumstances that a fridge is.

The bottom line, is that car AC systems do tend to leak over time. Sometimes it's minor, and more effort and expense than it's worth to find the leak. Other times it may be more obvious.

But regardless, it's quite easy to detect when a car AC system is low on refrigerant.