I have a '99 convertible and just recently when using the air cond and in vent mode, I noticed the fan blowing quite loudly, but not much air coming out of the vents. I tried to manually change the modes, and although the display indicated a change in mode, the air flow did not change. Any suggestions on diagnosing the problem?

 

If the ACT is good (I had to replace mine), it might be a leaky vacuum hose that controls the vent dampers. 8 years for rubber is like 80 human years

 

Thanks buddy. Excuse my ignorance but what exactly is the ACT?

 

Search on vacuum leak and you will find many posts including several of mine. The battery leaks acid. Underneath are 2 major bundles of mostly wires with a hard plastic vacuum line in each. One goes thru the firewall and terminates in a PURPLE connector. This SHOULD supply vacuum to the A/C vacuum switch which SHOULD change the vent doors. The real supply for the vacuum is in a different cable going TOWARD the engine. It took me 2 days to disect this cable and find the remnamt of the vacuum supply line. Both of these hard plastic lines go down to a vacuum check valve and vacuum tank just inside the passanger fender. Usually both lines are rotten and the check valve is shot also. Trim the lines back and then use rubber vacuum hose to connect to the plastic stubs remaining. I did the job multiple times because I THOUGHT that a lot of the plastic line was OK. IT WASN'T.
It failed again in a week. The check valve is $6+ at the GM dealer but the EXACT SAME VALVE is $3.48 in the HELP section of Advance Auto.
After replacing the lines you will be amazed at the air coming out of whatever mode you select. When you pull the battery to get to the lines mix up a couple gallons of baking soda and water and pour it LIBERALLY over EVERYTHING under the battery to neutralize the acid. Flush with water and let everything dry good. If you have the DELCO battery look for leakage at the terminals. I've had 2 leak at the positive terminal. Now using a SAMs $53 78N battery. Good luck with your Weekend job BIGHANK

 

Thanks Big Hank.

 

Sorry for the acronym, it stands for Automatic Climate Control. Mine had a bad computer unit and needed to be replaced. Works good now. Glad I could help.

 

BigHank - I finally started this process this past week-end, and yes there was some acid leakage. But I don't see any apparent damage to the vacuum lines thus far. I'm having a real problem however getting to the lines at the check valve. They're so far down in the fender. I removed the inner fender mud guard but am still having trouble getting to them. Any suggestions? Also, where exactly does the vacuum supply line connect to the manifold?

 

Is there an easy way of getting to the vacuum lines and check valve located at the bottom of the fender well under the battery compartment?

 

The vacuum lines inside the wiring harnesses are most likely disloved. You probably going to have to open up the wiring harnesses to fine the lines and check for damage. The sorce of the vacuum comes from a fitting on the back of the intake manifold. It is NOT easy to get at!!!! You either need to remove the intake or use an inspection mirror to see the line and 90 deg rubber fitting and plactic line. I have pictures that I can post later tonight.

If there was an acid spill, you have more problems than just bad vacuum lines!!! You need to CAREFULLY inspect the wiring, PCM TAC Module, Chassis and electrical ground connections and splice packs!!! This isnt an easy or quick repair.

BC