To awnser your question, Reddot corp. makes a roof mont condensor that works well.
Looks good ,just like you're roof AC unit with plastic cover.Down side is you have 2 hoses & wires to run up to the unit,
One thing you might check is fan stat.When thermostats opens usually around 180 will let water circulate it will cool some,As heat rises to around 200 fan stat will tell fan to kick in.your AC will make your fan run also to cool condensor if needed so you have a lot of variables. I would check coollant flow ( radiator as mentioned earlier) a swell as fan stat before I jumped to mounting a roof top.
