Hey Brickboard members!
I have a new friend that has worked on the heating and aircondition arena for 20 years. We where talking about the Brick and got in the Ac section, and I made the comments about the large failure rate of the evaporator and its composition aluminum. His first coment was that on the middle 80's some companies tried this on the condensor coils the unites that sit outside the house and the A coils inside the house also known as evaporator coils had a very large failure because the aluminum was been attacked my metal particles on the air, in others, it was reacting with the particles and creating pinhole leaks everywhere. Later on Volvo introduce the filter that sits outside the hood but the problem according to him, " any metal particles or slivers that the fan would produce has it wears out can attacked the evaporator because its between filter and evap. I think that S70's had the filter relocated to a position between the fan and evap. similarly to a system on a house. Aluminum also tends to fail when it freezes because of a clog drain. In some areas they use to spray a none reactive coating on the condensor similarly to a sealant and a popular name was micro guard 35. Recently, volvo has introduce the automatic ramp up of the fan in order to cool the coil and keep the moisture out. You can probably quess what the HVAC industry did after using aluminum they went back to copper after 2 years only. His final advice was when replacing that evaporator:
1. Don't use OEM but copper only,
2. You might consider applying the sealant if desire,
3. Make sure the drains are clear and might consider enlarging them,
4. When using Ac always keep the fan runing even after turning off: Low speed was fine.
5. Becarefull with the charcol filters they can minimize the amount of air been push to the coil and can freeze the condensor and compressor too.
6. Never run the Ac when the temperature is below 50 degrees: not very good to the compressor.
Feel free to add to my list!

No offence as I know you mean well here BUT for one, your friend (who knows home central air units, not exactly the same as cars) doesn't work for Volvo so then doesn't know that Volvo does now offer a "kit" that address's these issues. The kit's been out for about a year now but it's more $$$ than the evap alone and most Volvo owners decline to spend more money than necessary when they need a new evap from my experience, and I've been a dealer tech for many years before 850s came out in '92 in the US.

To my knowledge, there is no copper replacement evap made by anyone for Volvo 850s and probably for good reason, like perhaps copper won't absorb heat as well as aluminum or the demand isn't there for a manufacturer to produce them as they're unique to 850s, X70s? Just a guess. All Volvo and other auto evaps that I've ever seen are always made from aluminum. I've never seen a copper evap in any car and I've been a tech for 24 yrs now overall.

From what I've read here in the last year, those who've tryed 134a sealers have not reported success so that's perhaps nothing more than snake oil.

For an 850 owner to "check the drains" is not realistic although possible. Most won't remove the cowl cover to look but if they do clog, the water usually doesn't freeze inside the interior where the evap resides, it drains out through a drainage tube. The water will ruin a blower motor however, seen that several times.

As for running AC below 50 degrees, whenever the defroster is used and it's not so cold out that AC can't work, the AC compressor engages and there's no compressor shut-off switch to stop that.

In summory, do note that Volvo has addressed all of this for anyone who needs a replacement evapoartor BUT it doesn't come cheap. The kit consists of a new evap, pollen filter kit, accumulator (old one is probably saturated and moisture in 134a is VERY bad, produces acids mixed with 134a oil), and a piece of tape that restricts the airflow from the blower motor brushes so that metal shouldn't reach the evap. Installing this kit does require more labor than just replacing the evap only and given the choice, most 850 owners opt for the evap only probably because it's now an older car and they're not planning to own it forever (my guess) so they take their chances on an evap only.
If one were so inclined, one could remove the blower motor and add a piece of tape that cuts off about 1/2 the airflow from the smaller hole in the case, where the motor brushes are and I now do that whenever I replace a blower motor.

If it were my car and the leak was slow, like just needed some freon once a year, and I lived in a state where I could buy those 1 lb re-charge kits (not my state), I'd just top it off annually.

Also....SO far, the X70s which all come with a pollen filter installed at the factory have not had evap failures nearly as often as 850s and the evaps "look" indentical. Up until '01, the pollen filter was not installed between the blower motor and evap either but it is on '01 on V70s and all S80s, S60s, X40s.