I usually don't drive with the A/C on, but recently when I use it I am having a problem. Whenever I am cruising or idling my A/C works perfectly. The issue I am having is when I am accelerating. The A/C blower diverts the air from the front vents to the windshield & floor vents. When I let off the accelerator the air goes back to coming out of the front vents. Does anybody have any idea what is going on?
HVAC Issue
- Thread starter black2002gt4.6
- Start date
nyuk98gt
15 Year Member
black2002gt4.6:
Welcome to StangNet!
Yes, the ventilation doors have vacuum-powered motors. At light or steady throttle, you have plenty of vacuum so the doors stay where they are. When you step on the throttle, the vacuum drops and the doors start swinging like an old saloon when the drovers come to town.
Basically, you have a vacuum leak. You need to follow the tubing (it is tiny) from the engine bay (near the firewall) and back behind the radio (you may need to remove the radio) to find the vacuum Xmas tree. Maybe a hose has fallen off or the supply line has a crack in it.
I don't have any pics (because I don't have access to my shop manual). Your local library may have a subscription to AllData and there you can get a nice schematic of the vacuum tree.
HTH,
Chris
Welcome to StangNet!
Yes, the ventilation doors have vacuum-powered motors. At light or steady throttle, you have plenty of vacuum so the doors stay where they are. When you step on the throttle, the vacuum drops and the doors start swinging like an old saloon when the drovers come to town.
Basically, you have a vacuum leak. You need to follow the tubing (it is tiny) from the engine bay (near the firewall) and back behind the radio (you may need to remove the radio) to find the vacuum Xmas tree. Maybe a hose has fallen off or the supply line has a crack in it.
I don't have any pics (because I don't have access to my shop manual). Your local library may have a subscription to AllData and there you can get a nice schematic of the vacuum tree.
HTH,
Chris
wmburns
SN Certified Technician
+2 on the vacuum leak. There is a check valve in the AC control vacuum line between the vacuum res and the intake manifold. The purpose of the check valve is to maintain vacuum inside the vacuum res. I suspect either the check valve is bad or the vacuum leak is after the check valve.
Note, the vacuum res is in the passenger compartment right hand side. It is well up under the dash and can be difficult to access without removing the dash.
Note, the vacuum res is in the passenger compartment right hand side. It is well up under the dash and can be difficult to access without removing the dash.
Similar threads
