Check engine light came on it is giving the code P0442 on 2002 Kia Sportage

My car has about 145,000 miles on igt.
The code givin is pO442 SAY'S EVAORATIVE EMISSION SYSEM SMALL LEAK. What does this mean?
Also When it is hot outside and running the air condition it the heat gauge will go up to hot. Then we turn off the the air and gauge will go down. What can this mean?
Thank you

2 answers
Try these steps http://www.obd-codes.com/P0442
replace ur gas cap it is not sealing