This past week I have been having issues with the hvac controls, when ever I accelerate or speed up the heat will blow out the 4 vents on the dash. If I change the control to a different location it will change it, I looked in the engine bay and did not see any loose vacuum lines. It is a non- automatic hvac 4x4 98 blazer. Any suggestions would be greatly appreciated.

 

Your symptom indicates a vacuum leak. If the vacuum lines are OK as you mentioned, the vacuum check valve is not holding vacuum when you accelerate. This link shows where it is: http://i561.photobucket.com/albums/s...acuumlines.jpg Most auto parts stores stock them, cost is ~ $5. If that doesn't repair the problem, there is a vacuum leak The link shows where all the vacuum lines go.

 

Thanks, I did a lot of searching, but everything seemed to be opposite of what my problem was, I appreciate it.

 

Find the vacuum line under the hood that goes through the firewall; this is for the HVAC control. Remove the hose from the T and cap-off the T. Then go for a drive and see if the problem is gone.

Also the vacuum lines rot-out, especially the ones in the upper left area of the engine bay. Suggest just buying 10 feet of vacuum lines and replacing them all. Also check the check-valve for a leak.

 

I tried to pull the vac line from there and was not successful. I did not want to break the line, how easy is it to hookup the vacuum line that goes through fire wall back up? I might just replace it if it isn't too hard to do.

 

The HVAC line, (hard black plastic) goes from the back of the mode switch, through the firewall, and connects to a rubber line next to the ABS unit.