this is NOT a DIY question, i am trying to get a reality check on a contractor who insists he cannot do an install the way i would like to do it.
i have 2 specific questions but first let me describe the situation. i have a cottage in upstate new york (long cold winters and usually a fair amount of snow). about 30 feet away is the mouth of an old mineshaft (it goes horizontally into the side of the hill). inside the mine its about 50 degrees year round. this seems like an ideal spot for an air source heat pump. (see also hvac-talk.com/vbb/showthread.php?t=164426) specifically i am considering a fujitsu mini-split.
just because the mineshaft is near to the cottage doesnt mean its an easy reach, and i think my contractor is inventing reasons because he just doesnt want to do it. i cant blame him in a way, but i am paying. "the customer is always right" and i am here in this forum to do my due diligence and make sure my idea is, in fact, right.

the contractor says running the refridgerant lines that far from the house would subject them to failure due to freezing, that they are uninsulated and so any efficiency gains by placing the compressor in the mine would be offset by the temp loss in such a run, etc. yet an architect friend (who admits he is no engineer) regularly sees compressors installed at great distances from houses. the fujitsu spec sheet says max run of 60 feet with a max vertical gain of 40 ft. my placement is within those figures.

my questions: can mini-split linesets be run 60' outdoors? what if any additional insulation is needed? what addtional issues might be involved?

second: am i crazy to pursue this idea? the mine is much larger than than the basement volume mentioned in the thread referenced above, but even if the compressor did suck all the heat out of the mine i wouldnt be any worse off than if the compressor was outside at the back of the house (where it will be inaccessible to have snow removed from the unit during the winter) , right?

i am happy to clarify any part of this situation. i am hoping especially to hear from professionals who have run minisplit/heat pump linesets in exterior conditions.

thank you so much for your time.