I have been told (by a volvo tech)that the ac evap fails due to the upper engine mount going bad and causing ecxessive movement on the engine which in turn rocks the ac lines back and forth where they enter through the firewall resulting in the evap being cracked from the movement, don't know if it is true but i have replaced my upper engine mount at 45K miles with a poly mount and there is absolutly no movement.

i have 120k miles on my car and original evap, so who knows!

Dan

The real cause is that 134a and ANY moisture creates an acid which finds a way out on the very bottom of most 134a Evaps in any car. The same cars running R12 didn't have Evap probs.
I've seen R12 cars converted to 134a where soon afterwords the Evaps leaked, condensors too.

Dan, I think thats a bunch of BS.

I replaced the upper engine mount with the poly 2 pieces mount and, I agree with you, I don't have any increase vibration in the cabin.

I do believe that letting a wet evaporator dry on its own with all the dust and gunk , is more suspicious. Turning the ac off a couple of minutes before you arrive at your destination, and replacing cabin air filter every 10K miles is a good preventative measure.

Cheers;)
--
'88 240, '92 740, '98 v70 GLT John in Tampa Bay

sounded like crap to me also, but thought i would pass it along to the list.

I also belive the cabin air filter along with letting the evap dry out for a few minutes is a good measure against failure.

I also was told that they reengineered the evap on later models to fix the problem, this may explain why mine still holds pressure and i have never added freon to it.

Dan

I have seen many posts about failed evaps, but I still don't know what the failure is.

I know that they lose pressure and leak but where does this happen? Is there a regular point of weakness to the structure? Is it a metallic failure?

What is the difference between an old style one and a newer style?

Thanks
Matt 93 850 119,000 miles

On every one that I replace (many btw), they mostly leak at the very bottom part of the evaps, where gravity would keep a liquid. Moisture is a known bad thing in any 134a system as it causes an acid to be created when it mixes with the PAG oil. Anyone who teaches AC in regards to 134a will tell you that plus that info is also written in manuals. In time, any 134a system gets some moiture in the system so some acids then exists and finds a weak place to escape. BTW, the "so called" NEW Evaps are not lasting any longer as the originals. I know of a few 850 owners who've had to replace 3 Evaps so far.

On older Volvos that used R12, Evaps almost never leaked. I've been working on Volvos over 20 yrs and have never replaced an Evap on any 200 or 700 Volvo. I've also seen Evaps leak on 960s using 134a and older cars that were converted from R12 to 134a.
My 3 80s cars STILL use R12.

I live in Colorado, which is pretty dry, so I'm hoping our arid climate will
protect my '94 850 wagon, although my mechanic tells me they have replaced
some evaps. I don't use the A/C that much & also turn it off a couple of minutes before reaching my destination. Do you think that will help or am I
doomed? I've already replaced the sensor by the driver & a damper motor.
Thanks, Don in Denver