I have a 2002 Gmc Sonoma 4.3l and the issue is When i turn on the heater/ac control it blows out of all the vents no matter what the setting is on. any ideas? as this is annoying blowing in the face at all times
Check under hood between brake booster and firewall for split vacuum hose or hoses.
Rotted vacuum hoses in this area is common, as I found on my '03 sonoma.
Be sure to find the one that is connected to the vacuum reservoir in the fenderwell behind the abs system.
Ok need to add when i switch to say Defrost it blows on the defrost and just the front vents but no floor. If i switch to floor it blows on the floor and front vents. so i guess it is switching but for some reason the front vents are the ones always blowing air. Would this still be a vacumm issue?