When I try to merge a HDR panorama, my C drive(despite ACR not being there, neither my cataloge, neither ANY of the things i can move or change) it uses all avaliable space(88GB worth) just to spite me. Why is it doing this and what the heck can i do to make it target ANY other drive?
I close Lightroom and then magicly the stupid space reappears.
Besides the ACR Cache, LrC can quickly accumulate a big video cache, if you have ever had any videos imported (you can't change the location of the latter but you can limit the size, also Purge it, from LR Settings - General tab).
A C: drive with only 88Gb of free space left sounds a bit overfull to me anyway BTW. HDR merge might just be exposing a lack of general working headroom space.
Potentially the virtual memory paging file might be moved to another drive - may not be a good idea depending on your hardware - but I would definitely first see what further cleanup of unnecessary C drive contents is possible. User downloads and temp folders, system restore points...