Volvo Repair: AC, sad notes, shaft seal

Question
The AC on my 1997 Volvo 850 is having trouble.  When it gets
hot outside, the AC does kick on, but it seems to click on for a
few seconds then click off.  i can tell, because I actually hear a
click and teh engine strains when idling.  

It neve seems to be on long enough to ge cool, so as a result
mildly cool air blow out the vents.  

Answer
Hello Daniel, The 850 ,of which I have become on owner,only had a couple of sad notes. One is the Evaporator unit,over time the drain s get clogged not the a/c drain as much as the cowl drains.Dumpping ganden particles into the a/c housing and acting like a sponge,keeping the evap.box wet.corosion sets in and replacement is in order.Low freon, less than a 3rd of a lbs. will just let the comperssor"cycle".Not enough to refresh.The other is compressor shaft seal.This seal is not replaced separatly.One more A/C note,over time R-134 will disipate on its own  Four to 5 yrs. and you may notice a loss of effectivness.thank you and good hunting!  PKD