Why does the air conditioner works fine but no heat

A bit more info would help - like "nothing as in switched off" or "nothing as in motors all running but nothing gets hot".

If you mean that it all sounds and looks as though it is working but there is no heat, then it is possible your changeover valve is jammed. There is usually a four way valve which effectively decides which way your a/c is going to be pumping.

Other reasons are that on this model, it checks to make sure there is at least a 5C difference before it will try and work.

For more help, please be a bit more descriptive as to what it IS doing as well as what it is not - eg: fans / compressor on? strange noises, hissing / error messages and also indoor / outdoor temps