I have a 8 year

I have a 8 year old GE Cirulaire 230volt/ 2600 BTU Portable(window air conditioner). it's only used occasionally in rela hot summer days. It's installed in a wall and only accessable outside about 25 (3 stories) ft straight up. I've been using the Ac on and off for the past 3 days and all of the sudden today it just shuts off all by itself. I checked to seeif i had blown a circuit Breaker but no! Nothing at all works...no power what so ever. Now I waited about 20 minutes and tried it again an lo and behold it turned right on and worked fine for about another 6 -7 minutes and then shut itself down again. I've now repeated this 3 -4 times. It will turn on after I let it set for a while, but once it does go on I have to reset the temperature guide. I can't believe it Froze up...but what else could be the problem? I checked the filter and it's nice and clean. However getting the unit out of the wall or accessing it from the outside is a major undertaking. Got any ideas on the problem and how I might be able to fix it? **** Wray