My dad's air conditioner for his house went out. I don't have all the details yet but i am guessing compressor. The HVAC contractor is telling him that he needs to replace all the coolant lines between the outdoor condensing unit and the furnace. I havent heard of this before and all the lines are run up inside the floor joyce and sheetrock.it would be a major pia and expense. Is this a normal recommendation with a condensing unit replacement?

I did it when I replaced my A/C units, because apparently the new refrigerant needs bigger lines. At least that's what the guy told me.

If his system is an old R22 system. Some contractors would choose to soft solder the lines. The new refrigerant 410A runs at Double the pressure of 22 so all lines need to be brazed. So he may be telling the truth. Also R22 uses mineral oil and 410A uses p o e oil. So the lines would need to be flushed if they were braised. Could also be a pipe sizing issue if he is going with a larger condensing unit. If he is not recommending replacement of the indoor evaporator coil that tells me it is probably a 410A system. I would ask him why the lines need to be replaced. If the existing system is 410A I don't see why that would need to happen

If it is a solid line set and the right size for the unit the only thing that would need to be re soldered/brazed is the connections on the outside unit and the inside unit if it's being replaced. In all the years I did HVAC work we never soft soldered it was always a 15% silver solder. Eric

I’m an hvac installer and I’ve never soft soldered a line set. The only reason to change it would be the size. The new one will work with the old lines but maybe not as efficient. I would definitely ask why he needs to change it. I would also get several more estimates from other companies.

I've been selling and installing A/C systems for over 25 years and I started playing with the new refrigerant when it was called PURON by Carrier when they brought it out. I'm not going to get into brandsas I have my favorite and others have theirs. I have replaced hundreds of R-22 units with R-410A units on the existing copper. The only reason I ever change it is degradation or improper sizing. If the existing copper is the correct size and doesn't have a bunch of welds or kinks or other degrading I use it. I pass that savings on to the customer. Don't get me wrong it is no big deal to replace one running it up and out or under and out. If it has to come out the soffit a properly installed line set cover will give a clean appearance. They would have to give me a good reason for replacing a line set. And absolutely the NEW freon is not the answer. Also I have left the existing inside unit or evaporator coil if the manufacture says it is rated for 410A and is in good servicable condition and is rated for the new outside equipment size. Sometimes a good coil can be upgraded somewhat with a thermal control valve and fan speed. If it is an existing inside with an R-22 thermal control valve the valve will need to be changed to a 410A valve.So with all this mumbo jumbo said the answer to your question is no unless there is a viable reason to do so such as wrong size for new equipment or degraded in some way that can be shown and explained.