Just these past couple of days, I had an opportunity to take my C5 for an extended highway drive. 650 miles round trip, 95% highway. I really enjoyed the car, and it still keeps my blood flowing, even after almost 10yrs of ownership. Got 28.4mpg... not bad with 650+rwhp on tap.

Anyway, ran into something strange. Understand, I do not put a lot of highway miles on it, and honestly don't use the A/C that much, even in Texas, b/c my jaunts in this car are typically pretty short.

On the way to my destination, I left before sunrise, so it never got warm enough to turn it on. However, on my 320+mile return trip, I turned the A/C on while I was on the highway. It blows cold air, but it does not blow hard. If I turned the fan up (or ran it in the mode to recirculate the inside air) I could hear the fan spooling up hard (and it made a louder than normal noise), but the airflow was not increasing.

It seemed like there is/was a restriction somewhere in the ventilation system, but it wasn't just out of one outlet... it has to be prior to where it splits into the 4 outlets.

Ok, so I got home last night... parked the car overnight. Had to go get some gas in it this morning, and so I turned on the A/C again. Everything works perfectly. No restriction in airflow... it blows hard and is consistent, and responds to raising/lowering the fan speed. The loud "whoosing" noise I heard for 4 hours on the highway yesterday is gone.

I have not gotten on the highway today, but wondered if there might be some sort of inlet butterfly valve that might be closing at high speed that is restricting airflow? Thing is, on my return trip, after exiting the highway, that didn't seem to help the airflow problem.

Any other thoughts? I don't even know where to look, but I'll get out my schematic on the HVAC system. Would hate to tear apart the dash for something simple.

 

The problem maybe physical equipment. Something can be in the hvac air basket or a failing motor...Motor "Ball Bearings" may be worn and this is the first stage to failure...It is an easy check with the items on the passenger side of the interior above the BCM..Check the threads on forum above a removal..Takes 30/45 minutes to check and reinstall if it is not the problem...

 

thanks, for the advice. I will get under there and take a look.

 

Did you check it for codes first? Even an H code could point you in the right direction for an issue like this. Probably not the common vacuum line @ the back of the manifold if you have control of your directional airflow ventilation control.

 

I have not checked the codes...duh... that should be the first thing I would check.

Just very strange that it has always worked fine, then it doesn't during a long drive home, then today it worked perfectly.

Looking at the schematic, it seems like a valve actuator might not have been functioning properly...keeping the airflow restricted.

Blower motor pushes a lot of air, and even when I wasn't getting airflow, I could audibly hear the motor spinning just fine.

 

members often report air on one side but not the other.. many threads on resetting the actuators....

 

thanks, I will search that. This particular problem was not one side vs. the other... it was all 4 vents (well, can't confirm the far passenger side one, but I can the other 3) just getting minor airflow through them.