The contractor came out and installed a new run in heavier gauge copper than was the aluminum. The house was originally built in 1967 with baseboard heat. It appears to have been disconnected and the boards left in place. The furnace and A/C was added in 1973. Regardless, the furnace is working quite well, though I had to have it done on my own.
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"Any sufficiently advanced technology is indistinguishable from magic."
— Arthur C. Clarke