Rv rooftop a/c duo-therm quick cool

I started to small electrictial order threw the vents in my travel trailer, then the A/C quit working. I went up on the roof and took the top off and there is this part that looks like a small barrel with prongs on it that had a little black extension plugged into it . It looked like a little square fuss which was burned and melted. I took this part the barrel and the small square thing with the prongs on it to the A/C repair shop and they sold me this part {5466-1602-2241-1736} without the little square extension thing and said they have never seen the little extension before, so they sold me the part above and I installed it and the A/C worked for a few hours then it did the same thing, only it cracked. So I bought another one of the small barrel things above and put it in and turned on the unit and right away it blew the top off the part . The compressor seems to want to kick on but right away blows the part above. I do"nt know what to check next. Please help.