Can it be assumed to be always the case that if a part is replaced within the parts warranty period but outside of the labour warranty period and the new part is anomalous - say the new compressor is high amping - then the service company providing the priced labour just has to make the second change-out at it's own cost.

Or, provided the part is a genuine manufacturers part right for the job, could the service company say "Oops, new part is also faulty - will have to quote to replace this one too now in addition to the labour already provided".

Maybe the compressor fell over in the delivery van and now has a compression chamber flooded with oil. That does not matter - it is a matter different from the question.

What happens if 10 parts in a row are each time anomalous and the service company has quoted for just a day but now 10 days are required - 1 for each anomalous part. I can't imagine this actually happening but hypothetically what might be the case if it did.

Sure, if you tell the customer that there is something fishy with the system and further investigation should take place before the part is changed and they say "No, we have no time, it must run now - please just throw the new part in" then you must insist that they pay for the second and third change-out ed infinitum.