Not a very good idea when there is no load. The thing will cycle itself to death as pointed out earlier.
Op said it spent 30 mins at 32 degree return with machine off. If that's true why couldn't you shut down at 32 an bring it on at 40 or more? Wouldnt that be better than leaving it on with no load? Im not very experenced with centrifugals. Op hasn't stated how critical supply temp is.