Like alot of us, I am unable to get any heat out of my 97 F150 XLT 4.2L 6 cyc engine. I have changed out the thermostate but to no avail. I checked fuses and found the 15amp fuse for the AC blowes as soon as I start the truck. I imagine the actuator motor has shorted out and the blend door is stuck shut as I get no heat, but just not sure. I was able to put a new fuse in and the ac ran for about a minute and cold air blew out, but the fuse blew again very shortly afterwards. Anyway, I am not sure what is going on at this point but the blown fuses are a major concern and as I get no heat and live in Minnesota, I will need heat NOW lol, or very soon.
Does anyone have any ideas on this?
I feel heat on the hoses going to the heater block inside the truck so I imagine the blend door is stuck closed. Does the blown fuses have anything to do with the heat/blend door?
As you can tell, I know very little about this but I have taken my dash off before so no issue there. I just need heat and AC next summer.

 

What is the fuse # and which fuse box?

 

And this is in the inside fuse box under the drivers side. I got the dash out and checked the blend door and acutator. I feel sort of stupid as I was reading the manual and read the blend door is controlled by fuse #5, along with the cruise control. I have the pressure swith disconnected at the master cylinder so not sure why it would short out. I have cut the wires and put tape over them so there are no loose exposed wires. I did manage to take the actuater motor out so I can now get heat, and probably more then I will need, but at least I won't freeze this winter.
I followed the plans on here and put it all back together but now the truck won't start. Lol I will pull the dash back apart in the moring and check all the wiring harness to make sure I did not miss a connection. I sure hope I can get it started! I feel so stupid after all the work to find out I did not need to do any of it and now my truck won't start!

 

Back to original problem...

Fuse F5 feeds the following:

Backup lights via transmission-mounted switch
DRL (if equipped)
Cruise module (operating power)
Blend door actuator (you discovered this)
HVAC function switch (feeds A/C clutch circuit)

A short circuit in any of these devices or their feed lines will blow the fuse.

The switch on the master cylinder is on a different circuit (F13 probably).

Good luck getting it started..

Steve

 

I don't mean to hi-jack this thread, but I'm having the same problem. Except everytime I replace the fuse, it'll run anywhere from 5 hours to a week without blowing. I think it is the wiring on the back-up lights trannie switch that is touching something. When it first happened, my dad has the A/C on full blast and was backing up to a trailer. He shut off the truck, restarted (with A/C on full) backed up some, shut off and repeated abotu 3-4 more times. I don't have DRL's, I don't have Cruise, and my fuse only blows SOMETIMES when I go in reverse. Its just now starting to get cold here in Fla. I went to the dealership and the guy said it is 90% possible that I am right. Can anyone point me in the right direction of where to start looking? At 16, as soon as I'm under a vehicle, I'm lost. Thx.

 

I'd start by closely inspecting the backup light circuit under the bed of the truck towards the rear bumper, especially if you have hack-job installation for any trailer lighting harness. If you have the factory-installed tow lighting package, then I'd start by focusing on the wires to the individual backup lamps looking for any damaged insulation.

Steve

 

Well our pop-up Coleman camper has a brake system on it, so my dad installed a 6-pin round harness that transforms the factory 4-pin to the 6-pin brake system harness so we are able to control the trailer's brakes in the cab of the truck. Right now the 4-pin connector is disconnected from the 6-pin, and its been almost a week since I installed a new fuse and it has not blown out yet. Could this 6-pin harness or my dads installation of the 6-pin be the problem?

 

It would be the first thing I would inspect.

No disrespect to your dad is intended, I'm ALWAYS suspicious of ANY change, especially if it remotely correspondes to the appearance of a fault condition.

Steve

 

Gotcha, when I get home from school on thursday I'll roll out the floor mat and give it a look over. Err, what should I be looking for? A loose or discolored wire?