The same person who designed the 240 heater core, designed the placement of the AC evaporator. It a 10 hour book job to replace. This is true for any FWD Volvo.
What not to buy: 1993 850, 1999-2001 S80. Stay away from 2001 in general.
Tha early AWD were mechanical and costly to repair, the bevel gear tended to break if not cared for (lubed for life?).

The 1984-5 850 still had OBD boxes in the engine compartment, 1996+ cars require a scanner.
1999 was the first year for electronic throttle. The factory warranty has expired (10 years/200k miles). A Canadian outfit repairs them.
The turbo is extremely robust, it matches the white block in longevity.
The seatbelt rubs against the seat bolster, wearing off the leather(?).
The electronic climate control is the best in the industry.

Klaus
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I am not a mechanic, so can you trust what I type?

In general, AVOID pre 2001 S80, all accounts suggest a real horror show. 97 850 and 98 S70 tend to get the highest marks, post 98 S70 has the ETM issues, although those can be dealt with. These cars are now old enough that the specific car is more important that the year. i.e. You would rather have a totally cherry 94 850 than a poorly maintained 98 S70.

Many early 850s lacked the pollen filter, which will ensure that the AC eventually fails, a real expensive fix. While some claim that all 850s are affected, my 96 had a pollen filter from day 1, and the AC has never had a problem.

The 850 turbo motor is a very impressive engine for those, like me, with a fat right foot.

Check out by a Volvo competent mechanic is a must.

Good luck.