If the compressor runs for a few seconds then goes click, it is normaly the compressor that is faulty, would need an engineer to confirm this as could be a faulty relay/ptc unit but unlikly
It’s almost certainly the compressor that’s goosed then, there’s an outside chance of the relay or TOC but I’d doubt it. A T450 should be a few years old now I should think and,if it is the compressor that’s gone, in all honesty it’s not worth repairing. 🙁