4.2f1502002

I know there have been a few threads started about this topic, but none of them actually helped me out. I started to notice that when the engine is under load and in overdrive, the air coming from the panel will go to defrost on the windshield more frequently. There's a hill I have to go up when I come home everyday and I notice that as soon as I start putting a load on the engine to go up the hill at 55-60 mph, the air will move to defrost until I reach the top of the hill and let off the gas pedal which will then cause the air to return back to panel. It took me a while to notice it and the more it occurred, I realized something is causing it to happen because I'm sure its not normal. I googled this topic and most say there is a vacuum leak somewhere. I don't want to take it to the dealer as they would probably charge me an excessive amount of money just to find the leak and then do the repair. I'm sure someone has had this experience with their truck and would appreciate the help in hopes of fixing this issue.


My truck is a 2002 F150 XLT SuperCab with the 4.2 V6 with roughly 116K miles.

jstockert

A "few" threads on this topic. There is usually one a week. Do another search.

twoskinsoneman

there is a vacuum actuator that holds a door blocking air to the defrost when it's under vacuum. Your vacuum circuit is obviously losing it's vacuum when your engine is under load and vacuum in the intake is it's lowest.

I had a similar problem. I bought a handheld vacuum pump and started isolating the vacuum circuit. First I found where the vacuum line went through the firewall on the passenger side near the 4x4 solenoids. I unplugged it, and connected the pump to it. Then I put the control in "floor" mode and pumped. Using the pic below I checked various positions and checked if the vacuum held.

My problem was actually ahead of that point. But systematic checking of the vacuum circuit as I described will tell you where your problem is.

4.2f1502002

Can you take pictures of where you are talking about under the hood? I am unsure as to where you are talking about.

twoskinsoneman

I'm at work at the moment so I grabbed a pic on the internet.
You can see all these vacuum lines and connections behind where the battery would be. One of these black lines off one of the "T" connectors leads straight back through the firewall. It's the one that provides the vacuum for the HVAC controls.

Cmanjr

Sorry for the thread jack, but my air won't blow to the floor. Everything else works perfectly fine, just no air blowing to the floor. What needs to be fixed to make it blow to the floor again? And how hard would it be to do/get to?

twoskinsoneman

look at the picture in this thread I posted showing the doors and vacuum lines.
The vacuum motor that control the air deflection to the floor is called the floor/panel door motor. It has the blue and yellow vacuum lines connected to it. You can see a photo of it on this recent thread:
https://www.f150forum.com/f6/97-f150...lation-274540/

if the floor is your only issue I would check the operation of that motor.

Cmanjr

Okay cool thanks. Where could I get a replacement motor if mines bad? And how hard is it to get to the motor? What all needs to be removed to gain access to it?

Carcrazygts2

To the OP the little blue thing in the picture is the vacuum check valve. Thats what needs be replaced.
[MENTION=174898]Cmanjr[/MENTION] You probably have a bad blend door.

Cmanjr

I'm confused now. I know there's a blend door for the heater, but what other blend doors are there? And when I turn it to the floor setting it blows from the defrost only. everything else works as it should though. And what about the motor he was talking about above?