Air blowing through vents

It is probably a problem with the mode doors and the air is being directed elsewhere.


The mode selection is done through a series of air doors that are operated by vacuum. When there is either a partial or total loss of vacuum, the system will default to either defrost or on some vehicles, heat. Acceleration can also have an effect on the doors for the same reason.

Look under the hood for a small black plastic hose coming through the firewall. Follow it to the vacuum source looking for any breaks, cracks or leaks. Also, follow any other lines that branch off because they may go to a vacuum reservoir (storage tank) and a leak there will cause the same problem. Using a vacuum gauge to determine if you have full vacuum at any given point is the best way to find it. You can cut into the line anywhere and splice it back together with a piece of vacuum hose. Find the broken line, you found your problem.

I thought that too. Tested all the lines and they work perfectly. And to go the extra step i can physically see all the flaps open and close as they suppose to, i can see it go from window defrost to vents to floor, they all open and close when I turn the knob to its destination. Tested all the air actuators that controls the flaps and they all function. Blower motor works just fine. Even for giggles i did a radiator flush. Problem still exists, i get only a breeze coming from any vents i choose. I did find it strange that when i took the blower motor out that the flap to the outside air (leading to the firewall motor compartment) is open when i have the directional knob placed in the "off" position and that actuator that is controlling that flap is getting air to it to push it open. But as soon as i turn the knob to anything else such as "vent" or "defrost" that flap closes and that when that runs the actuator motor thingy stops pushing air. There is no cabin air filter and no signs of any air blockage except for that door next to the blower motor closing when the fan turns on. Maybe why i am only getting a breeze through any vent is it cannot push air because it cannot pull in air? So if it cant draw in any air it cannot push the air through. Kind of like if you put a fan inside a tube it would work. But as soon as you block off the side that it needs to suck air in to circulate properly it will not be able to push air out the tube properly until you open that side of the tube back up that you previously closed. Then it works again. Just using an example on my train of thought.

All that flap does is switch from inside air to outside fresh air. It does not cut off supply.

Have you recently changed a blower motor? I have seen a number of times where the wires get switched and the motor turns backwards.

I have not changed the blower motor yet. The wires clip in only one way. I can try to see if i can reverse those wires somehow.

Also, make sure your evaporator is not clogged up with anything like an old plastic bag or pet hair.

I will take a look, thank you for your help getting me this far.

I would take a look at the mode door actuator to see if there is something wrong there here is the location.

Check out the diagrams (Below)

Let us know what happens and please upload pictures or videos of the problem.

Cheers, Ken

Thank you. Took a look at it. It appears that everything is functioning normally. I even with the extra mile and take a look at the intake lines see if it was clogged and from the fan to all the vents. No clogs. That really leaves me with two options that I can think of now. A resistor is bad or the blower motor is bad. I took the motor out and tested it and i immediately regret that cuz I kicked up all the dirt from a passenger floorboard. Still a puzzle to me.

Can you hear the blower motor working when the system is on? Maybe you can take a video of the problem so we can be on the same page. You can upload it here.

Cheers, Ken