There hasn't been any good feedbacks on portable air conditioners on Lowyat. Most people say stay away..

i had about the same issues  with 1 of my daikin AC during start of MCO a year ago.
On power ON  it works normal/cooling  for about  15 mins  then  the cooling slowed done  and
i could see  the IDU fins  some parts  not getting cold ./ no water condensation.
I cleaned the IDU fins with AC cleaner spray . but still  same issue.
i thought maybe not enough gas  or something faulty so just  left it  . this bedroom  not in use/  guest room.
A few month later i had time  to  climb the  kitchen roof  and saw  that  the ODU  was  clog with a layer of dust.
used AC spray cleaner to  clean the ODU fins. 
After this  i test the AC  and  wow  it works  all normal  now with great cooling .
i guess its  about  4 year  since new  i did not  clean/check  the ODU  fins . 

Lesson learnt .. is need to  do regular cleaning service  on the IDU and ODU  fins .

if you experiencing  poor cooling performance  , the first thing  to do is to check and clean them.