I have a 91 Chrysler New Yorker which I will keep for 1 more year.  My ac is blowing
hot air, and I was told I had to be changed over to use the new freon, and my undestanding
changing over is expensive.  Can't I just get it recharged with the old freon instead
of changing it over or should I spend the money?  I have 65,555 miles on it and it's
still is a decent car.

 
Retrofitting, or converting to R-134a does not always require great expense.  Sometimes, service port adapters and synthetic refrigerant oil are the only extra expense.  Not all cars are created equal though.  Some vehicles will require additional high side pressure switches, and other vehicles may require condenser replacement - or - condenser fan upgrade.  Since R-134a is less efficient, sometimes these changes are necessary.  This largely depends on how the vehicle was originally designed.  A system that performed marginally with R-12 will probably require the most retrofit associated cost.  Also, if the system didn’t work at all with R-12, it certainly won’t work with R-134a.    

 
One advantage of retrofitting is the potential long term savings.  Once the vehicle is converted, and it’s done correctly, any future service or recharge should cost less since you’ve already retrofitted.  For example; let’s assume you have your 1991 Chrysler New Yorker in to have the A/C checked.  You plan on keeping that car for at least one more year, maybe two.  The technician checking the A/C doesn’t find any leaks, and believes the system should perform well with R-134a, utilizing many of the existing components.  He plans on replacing the refrigerant oil, receiver-drier, pressure relief valve, high pressure cut off switch, and adapting the service ports with conversion fittings.  The total cost to you is a hypothetical $330.  He has plenty of R12 too, and gives you a second estimate so you can make an informed decision.  His second estimate consists only of evacuating and recharging you car with R-12.  That estimate is a hypothetical $220.  Nearly half that estimate is refrigerant alone.  You compare the two estimates and figure retrofitting will cost $110 over the R-12 service.  Now, here’s where the savings can kick in.  Let’s assume our technician doesn’t find any leaks, but you know from experience that each year you need to get the system recharged.  Otherwise, it works fine.  Based on that, let’s assume if you keep the car two years you’ll probably have to get it charged twice.  If it’s already been retrofitted, you might be able to get that evacuation and recharge done at any shop in about one hour for roughly $100.  Total cost for two recharges including the retrofit, $430.   Let’s assume you don’t retrofit and keep charging it with R-12.  In two years that should cost $440, based on $220 per recharge times two.  Hey, what’s ten dollars over two years?  Besides, R12 works better and keeps you slightly more comfortable.  Ah, but what if you have that first R-12 recharge done and it only lasts one month.  With an A/C system that old, it could spring leaks at any given moment.  After all, those old components won’t hold forever.  That’s where R-134a could save you.  After one month, Mr. Shop owner may even re-check that system and quite possibly recharge your car with R-134a as a goodwill gesture.  Who knows?  Maybe he wants to do his part to make things right.  He explains that he found a minor leak, maybe a loose connection or a leaky Schrader valve.  He tightens it up, and sends you on your way.  Now, let’s assume we’re talking R-12.  You know, Freon, that jug they keep locked up in the office.  Are we likely to get any goodwill gestures out of the jug they refer to as liquid gold?  In this case, you’ll most likely be on your own.   One month later, you’ll not only be faced with a leak repair, you’ll need to shell out another $220, again, largely due the cost of refrigerant.

 
Here’s something few people consider.  Since our hypothetical shop owner may be reluctant to give away his remaining stock of R-12 for warranty concern, he could become overly cautious in his leak repair estimates.  In other words, he might price suspect parts as insurance against future leaks.  Now, that car you plan on keeping for two years will cost much more to repair.  Not necessarily because your mechanic is a crook, but because it’s important that he contain this expensive gas.

While Chrysler recommends retrofitting as an option should R-12 become unavailable, we think from a cost perspective it may be the right choice to retrofit now.