Alright, having issues with the blower motor, or the heater box, not sure which.

So when I have the heat on in my truck, on Vent, driving down the road it will occasionally switch over to Defrost on it's own. Then it will eventually switch back to Vent, and so on. Also what it is doing is now when I have the air turned OFF, it is blowing air on the Floor, and Defrost at the same time. Was wondering why it was staying warm in my truck with the air off!

So any ideas what is going on here?

 

I would check the blend doors.

 

Vacuum leak. The vent system runs on vacuum, and if there is no vacuum, it defaults to defrost. Check the vacuum line going in the air box over the blower motor.

 

Thanks, I'll start with checking the vacuum lines.

 

It is this one most of the time:


/

 

Thanks for the picture, I will try and have a look under the hood tomorrow.

 

One of them vacuum lines (not the one in the picture but the one that goes to the vent selector valve from the engine intake manifold) has a check valve in it. If that valve is missing or the line's split/crumbling where it connects to the valve (and especially if you've also ditched the vacuum accumulator) then when you give it much more than half throttle you'll dump all the vacuum from the vent controls and end up in defrost.

 

How do you "ditched the vacuum accumulator"?
It is part of the heater/ac box.



/

 

Checked out the vacuum lines that I could find... and none appear to be cracked or broken. What's next?

 

Unhook the vacuum line from the check valve in the photo below and use a hand vacuum pump and see if you can pump it to a vacuum.
Also check the vacuum hose going to the check valve at idle and see if there is vacuum on it.



/

 

I don't have a hand vacuum pump, I suppose I could buy one.

I can check that, also how can I check the blend door? My dad said maybe that is just getting stuck or something.

 

The blend door not vacuum operated. It is cable operated and would not cause your problem.

You can rent a hand vacuum pump at most auto parts stores and then get your money back when you bring it back.

 

Alright thanks for the info. Bill

I think tomorrow I will run into O'Reilly's and pick up a hand vacuum pump.