Car problems..

Desiree • Due with my rainbow baby Aug 6th Derik J McMurray
Really wish this wasn't as stressful as it sounds... But the reality of it is literally the biggest headache ever... I'm 7 months pregnant btw...
So my fiancés car that we've only had for 3 months decided that it's air compressor was done and went to heaven(byebye) We live in Arizona so having AC is extremely important. We bought the car used since it was the only thing we could afford and that we were actually approved for at the dealership. We have horrible credit that we've been working our asses off to fix and slowly but surely it's improving. So when we bought the car it was completely unnecessary to buy a warranty with the car. Everything worked perfectly the mileage on the car was good and honestly the warranty was just way over our budget. We didn't plan on keeping the car for more than a few years it was basically to build our credit until we could get a better car. Well... After going around town trying to find the best deal to get the car fixed we eventually decided that we should go back to the dealership and hound them down to get the best price and to see if we could finance the work into our current loan since we don't have the money to throw at it. After they came to us with the price we literally wanted to fall on our knees and beg for something better. We don't have any extra money because of baby on the way and baby is more important then anything else in the world to us. 
So now the dealership is trying to get us in a brand new car(something we couldn't even do to begin with) they said they would buy out our loan(still don't know if it will be in full) and already got us approved through a credit union and our payments would be around the same price and blah blah blah... But honestly my biggest concern is, is this really a good idea... Are we about to make a huge mistake... Or are we saving ourselves in the long run.. I have no idea. I've been bugging the hell out of my dad trying to make sure I don't make a huge mistake(he's very good with decision making) but it's more like my parents are trying to get me to make my own decisions and my own mistakes so I can learn from them. 
Just getting the new car sounds like the easy way to go but I really don't know if we're about to get our asses handed to us.... We're going down to the dealership tonight and they want an answer from us then... 
Am I over thinking this or is this really a stressful situation?