Originally Posted by John
i have a problem when i accerlerate or cruising at high speeds in overdrive. my a/c starts blowing from the vents to the defrost. it's really anoying. i was wondering if anyone has had this problem and has any info on this problem. i think i have a vacum leak some where. i do not know how to find it. any info is greatly appreciated.
You are losing vacuum to the A/C servos under the dash.
There is a vacuum reservoir below the engine air cleaner housing that is supposed to maintain vac to the A/C system even when the engine vacuum drops as the throttle is opened. The reservoir has a check valve on the port that connects to the engine.
If you have a bad check valve, cracked reservoir or damaged vacuum line, you will get this defrost default symptom.
Look the reservoir over for problems, then check its two vacuum lines that go to the engine and A/C box on the firewall. There is also a small chance that the vacuum leak is under the dash.