This is a followup to my post a couple weeks ago about my tenant wanting the A/C set to 65. I had a technician come and look at the system, and he said there is a severe kink in the line that could have been caused by ice falling off of the roof. Since we never set the A/C lower than 74 or 75 when we lived there, we probably never noticed, but it is restricting the flow and causing pressure well outside of the specified range on both the high and the low pressure side of the system. To repair it, he will have to replace that section of the copper line, possibly put in new refrigerant of the old, expensive type, etc., and the estimate is about $1300. The condo is 15 years old, he said the unit is 17 years old.

So, I'm pretty sure I should go ahead and replace the A/C unit because there's no telling how long it will last and $1300 is a lot to spend considering the age. Plus, I don't want my tenant without A/C for a month and a half if I can fix it now, while it's still (mostly) working.

My main question is, should I replace the furnace at the same time? My mentor who has owned and managed a ton of properties in his career always replaces the A/C and the furnace together because they're typically the same age and he doesn't like to have them mismatched. But would you others leave the furnace while it's still working or go ahead and replace them together?  I can afford to pay cash to replace the whole system, but obviously don't want to throw away money if there's no need.