If the trigger to close the relay is on the compressor circuit, I agree it wouldn't overload, but if the fan is on the compressor circuit it might. I can't really see a need for a separate fuse since I think everything is fused elsewhere. That was one other factor in thinking it was a separate circuit.

Having looked at the schematic, it looks like the installer is using this relay to trip the pressure relay. I didn't realize the pressure switch had a separate relay (low speed) in addition the temp relay (high speed)

If blue is off the compressor (he said compressor harness, so it might be the compressor or it might just be wrapped in the bundle) and goes to 85 or 86, and yellow (ground) goes to the other; then it'll close red and black whenever the compressor is switched on, and the fan will run at low speed.