By using this site you agree to the use of cookies.Written One potential problem with portable air conditioners is the condensation back flow which should be exhausted outside through a hose - dirt and debris can accumulate if not properly cleaned; depending on the design. A unit used for one season shouldn't be a problem, though, and they generally last quite a long time - essentially indefinitely if it's well designed and constructed, and properly maintained. Buying used is always a crapshoot so it's really a value-judgement decision: is saving $100 amortized over a few years worth the risk of potentially buying a lemon without a warranty. I'd feel comfortable enough to buy used because I feel sufficiently knowledgeable to know what to look for and fix it if it breaks - a risk I'm willing to take.    EASY ANSWER:Plug it in, and make sure it is working!NOT SO SHORT ANSWER:Bring a thermometer to take the temperature of the air. You want to measure the Outside Air temperature, the Condesner Air temperature, the Supply (cold) Air temperature, and the Inside Air temperatre. 

You want to measure that heat is being transfer across both coils, and that the unit is doing work.Example:80F Outside Air95F Cond. Air Temp= 15 degree difference70F Indoor Air Temp55F SUpply Air Temp= 15 degrees differenceYou are rejecting heat from inside to outside and doing work.  Example of no work being done, but "feeling cold air"60F Outside Air70F Cond Air Temp=10 degrees80F Indoor Temp70F Supply Air Temp= 10 degreesYou seem to be doing a 10F split across both coils, so WOHOO, BUT WAIT!!!!goodman ac unit partsIf we think about this more clearly we can see the outside temperature is colder than the indoor temperature and we are unable to cool the indoors, AND have a paltry 10F  split.  ac and heater costSo what is likely happening is that your AC system is acting more like a dry cooler, meaning that you are cycling the refrigerant outside, rejecting some heat and bringing it back in, but your compressor is acting more like a pump and this only seems to be working because the outside temperature is so low you are naturally going to have a heat transfer toward the outside.  army ac unit