Segregating two combined assets to claiming a loss for one

Rental property: I'm depreciating an A/C compressor and air handler installed several years ago as a single system. I paid a non-itemized price for the system. Last year (2020) I had to replace the compressor but NOT the associated air handler. How can I segregate the old compressor cost from the original combined system cost in order to claim a loss for that one item?