Slide your sliding door back far enough to allow for the vent hose.
Vent portable ac through garage door.
Some portable ac units come with sliding window sliding door kits designed to help you adapt your sliding door area for a vent hose.
Gulrear sliding door air conditioner kit max adjustable length 220cm 87inch sliding door ac vent kit suit for 13cm 5 1inch exhaust hose 4 3 out of 5 stars 434 48 99 48.
In normal cooling modes portable air conditioners evaporate the collected water and send it outside but just circulating the humidity over and over is a waste of electricity.
If a window is not an option the other choices would be venting through the roof or wall.
Issue of venting the portable air conditioner.
One option which seems to be preferred by some people is actually using a wall vent to remove hot air from a portable air conditioner.
If you need to run a portable air conditioner without any exhaust vent tube set it to run in dry or dehumidifier mode and connect a garden hose to the top drain port so you can collect condensed water in a bucket or floor drain.
Garages usually do not have a traditional sliding window which is the most common way to vent a portable unit.
The air conditioner must vent the hot air somewhere.
This would require drilling a hole through the side of the garage to fit the exhaust hose.