Chosen Solution
Do both the fans in a mid 2015 MBPr with a discrete AMD GPU work in conjunction, or is one the CPU fan and one the GPU fan? If so, which fan does which?
Each fan is controlled discretely based on what is in need of cooling. You can see this with a good temperature monitoring app like TG Pro. If you suspect you are having a problem I would encourage you to install this app and post a screenshot of what it shows (sensors & fan) so we can try to figure out what’s wrong. Given the age of the system it maybe covered under warranty. Update (11/11/2015) Download the App I pointed out to you it will clarify things. The dual heat sink model has the heat sinks tied together by a common cooling bar to the two fan unit radiators which allows them to share some of the heat load from the discrete CPU & GPU. Why are we picking this apart, you can’t alter the design nor should you.
