This Volvo is new to me and I am attempting to get some of the bugs out. As it is a hot July the A/C problem has come to my attention. When the climate control system is set to AUTO (and A/C is ON) it works OK only until I accelerate, then it stops blowing cold air from the dash vents and instead blows hot air from the defrost vents. The A/C system has been checked and recharged. (It was low on freon but showed no leaks.) I can use the A/C without this happening if I turn the knob from AUTO to dash vents, which is obviously the simplest fix, but I wonder what's going on and if the system is actually working as well as it should since I don't freeze after the A/C has been on while, which was my experience with my last Volvo. Also when I turn the A/C OFF and turn the fan to 0, I still feel some air (warm) coming from the dash vents. Thanks for any insight you may have.

Before you try all that under dash stuff, check the big vacuum hose that goes down to the underside of the front bumper. You will see where the hose goes in but, the vacuum reserve canister is a little hard to see. On the opposite side of that canister is a plug that is in the opposite place where the hose goes , that plug gets dryrotted and falls off causing a big vacuum leak. Every time you step on it it looses its reserve vacuum, which can cause it to blow out of the defrost vents. I hope thats it.

Replace the two check valves first (behind big A/C silvery thing under hood) but it is probably the vacuum bellows (servo) under the dash.
This is tricky but not impossible to replace.
Consult the FAQS and my posted two cents worth on the subject titled "I changed a vacuum bellows and survived"
When it is fixed you will notice a large improvement in cooling under AUTO mode.

Good luck,

Dan

Likely one of two problems:
-failing vacuum check valve under the hood (easy fix)
-failing vacum servo under the dash (not so easy)

See the FAQ "heating" section for more information and pictures.

I have the same problem with my car with the manual climate control. My mechanic disconnected and plugged the yellow vac hose as suggested for auto systems. It still redirects to the floor under load.

He still think it is the vac servo. I am not sure.
Is there any data on this in my type of system>
Help, it gets hot driving quickly in there

93 945 MCC