Defroster blowing when turning key on

[250TUFF]

A couple of days ago, I went to start my truck and when I turned the key on to wait for the glow plus to go out the defroster blower/motor was on high. I have the climate control and it was turned off. I turned the key off and back on, but the blower kept blowing on high. Once the truck started, I turned the AC on and the AC blew out the vents like normal and the defroster stopped. The truck still does this now after several times of stopping and starting.

I did some google searching saw possbile vacuum issues. Below is what I checked. I did not want to do more without checking with you guys because I know some of you all know what the heck you all are talking about.

What I did:

Pulled all 3 electrical connections, 1 at a time that is connected to the vacuum pump and it had no effect.
Pulled the small hoses that are connected to the vacuum pump, 1 at a time and not difference.

I do hear the shift on the fly 4x4 engaging/disengaging each time, so that appears to be working. It comes on each time I try it even while I testing the electrical and vacuum connections.

What is my next step? Do I by a vacuum gauge tester and go that route, or take it to the shop? I am not a mechanic, but can do minor stuff? I decided not to start tracing the vacuum lines before posting here and checking in with you all.

Thanks in advance.

Tom

[Term3]

When you say you turn on the AC is your climate control in auto?

[250TUFF]

Yes, climate control in auto.

[Term3]

Mine does the same thing. With the climate control in auto when you first turn the ignition key on the climate control comes on and sees a big difference in the temperature inside your truck and the temperature that you want it to get to so it goes into a maximum cooling mode which is high fan speed and defrost vent outlet position. I find it rather annoying when it is in this mode so I just raise the temperature set point up a couple of degrees above the actual temperature so that the fan slows down and it starts blowing air out the front dash vents instead of the defrost vents. Once it swings over I lower the climate control temperature set point and it will stay blowing out the front dash vents at a slower fan speed.

[250TUFF]

THanks. Mine never stops blowing high even when the temp stabilizes. Dang thing.

[Term3]

I've never waited long enough to see if it would switch from the defrost vents to the front dash vents on it's own. I just raise then lower the temperature set point. Stupid thing.