GP60 (and other EMD) air conditioner question

I model Norfolk Southern in N scale (as well as CSX) and have noticed that the “big guys” have air conditioners mounted on the cab roofs on the GP60, and several other types, but my models do not. As ive started to detail my fleet, i wish to add these to my models, but there are two types listed in the Walthers catalog. “prime” and “vapor”. Which type do the NS GP60s use, and what is the difference anyways? Thanks, Azure

NS GP60’s were originally delivered without air conditioners but recent photos indicate they are indeed being retrofitted with cab rooftop A/C units…sorry but I could not find what type they are. Prime and Vapor are two brands of locomotive A/C units.

These seem to be showing up on almost all of NS more modern power. I did some looking and it is difficult to see, because even though a good majority of these are painted white, finding a shot to see the roof has been challenging. I also looked at their similar GP59 units, and not much luck there either, as I assume they would be identical. I did see this:

That looks like a Prime to me with that vent in the middle instead of the side.

It appears that my link didn’t work. but check out some on railimages.com, and you’ll run into a serviceable photo.