The size of the outdoor unit (surface area of condenser) has a large part to play in how the aircon can handle let's say -10 celsius outside while still giving you 20 celsius heat inside, or be 50 celsius hot outside and get down to 22 celsius cool inside, that's the basics of it.
I used to do my own split installs (for me n family only) when you could buy them with copper pipe included and still have my ebay vaccuum pump and gauges, still just as useful for gassing car aircons with bbq gas (no arguments pls this is not the thread for it), although hychill is much cleaner as bbq gas is not filtered good.
Bit of digressing there...

