I assume your speaking of a portable AC system that uses a hose that is set into the window to blow the hot air out?
Yes these can be fixed to some extent. However depending upon the issue with the unit, it may not be worth spending the amount of money to get it done. Sort of the weakest link issue.
Most of the times these and small window units themselves really do not fail, they just get real dirty on the coils causing them to lower their ability to cool If any cool air is coming out of the unit at all, then most likely its the coils and fan that may require cleaning.
Parts for many of these units can be purchased at HVAC suppliers but when you add cost of material plus labor, your better off recycling the unit and buying something newer.
What's wrong with it?