1986 f150 2wd 302 v8 5.0 automatic xlt lariat,

Hey everybody Andrew again,

Finally finished other stuff on the truck and now am tackling ac. I will explain the problem and things ive done so far with the system. So the problem is that i am getting very low air flow out of the vents. I did the usual stuff of taking the blower off and checking just the basic vent doors to see if any clogging or debris, checking interior vaccum lines and it looks pretty good. I took the blower off and tested with just the wire and the different settings (low, med, high) and the fan changed speeds and felt pretty new with visually almost no wear. (Low 12v - High 12.4v range of switch) Next in line is the evap core so i went ahead and cracked the case open and looked inside to my suprise that it looked pretty new (pics below) and still shiny. Instead of taking it off and wasting fluid i just did a test with the blower going and me hand feeling the airflow through the core and it was fair. Now the two things ive noticed is that 1 there is a cut vaccum line up on top of the heater core (shown below) and that the defrosters are basically always blowing air no matter the switch. So what i am thinking is the vaccum leak is causing the defrosters to stay on which is causing lack of airflow, idk just a guess. Yes a/c does get kind of cold when set to max, and heater does also work. If you guys have any suggestions thatd be great! This truck has many owners and from past threads you know i have had a nutcase go through and do things to the truck.

ALSO just found this im assuming resistor with missing pins and all sorts problems and thought this could be a problem and if it isnt it should be lol (last picture)

 

How about the airflow through the defroster ducts? Is that good and strong? Airflow leaves the fan, passes through the AC evaporator and then the heater core, and then into the ductwork. Vacuum operated actuators move doors within the ductwork to route the airflow to the correct destination, either the defroster, floor, or the vents on the face of the dash. To make sure you're fixing the correct thing, is the airflow itself good and strong, even though it seems to always be going to the defroster? Or is the airflow also weak in general?

Here's a good diagram showing the airflow:

A/C & Heater - Gary's Garagemahal (the Bullnose bible)



You are looking on the downstream side of the evaporator. If there's any crud trapped by the evaporator (there usually is), it will be on the upstream side, closer to the fan.

With the fan removed, you can kind of see around the corner to the upstream side of the evaporator, but not very well. An even easier method is to remove the resistor pack, the red rectangle shown in your last picture. Look inside there and expect to find some debris. Please read this thread about the danger of debris building up around the resistor pack, which gets very hot in normal operation and can start a fire:

https://www.ford-trucks.com/forums/1...n-the-cab.html

You can usually clear out any debris with the fan and resistor pack removed. If you want to go deeper, you can swing the AC evaporator out several inches without breaking any connections or needing to discharge the system. I forget all the details, but I think you have to remove the fastener that secures the receiver/dryer (the big vertical can) to the housing. Open the housing, as you have already done in the first picture. The flex lines will have enough give to allow pretty decent access.

If you really want to go overboard, I fitted a piece of coarse window screen on the upstream side of the evaporator. My evaporator had become somewhat clogged, with lots of fine debris getting caught in between the fins. By adding the piece of screen, in theory that should catch most of the crud. I still have to open the case for access, but if the screen clogs, it will be a lot easier to remove and clean that, versus trying to clean out the evaporator again.



Okay, then fix it. Need any more difficult problems solved?


This is a very good guess. The actuators for the different doors are spring-loaded to send airflow to the defrosters by default. The basic idea is for safety. In the event of a vacuum leak (such as a cut line, for example...), the defroster will still work and keep the windshield clear.

 

If you have access to air you can back blow the evap coil with the fan & resister pack removed.
Just note dirt will be blowing all over the place even inside the truck!
Dave ----

 

Hey eveybody, thank for the suggestions. Im heading out right now to take a look at the resistor hole and such and will let you know about the defroster speed, from what i remember the defroster is stronger than the vents. Id love to fix the vaccum line lol but i have no idea what it goes to! It stops 3 inches out of the firewall and with no signs of other lines in sight. Ill keep updated!

 

Alrighty,

Hey kr, the defrost vents are flowing about a medium speed? Dont know what max feels like lol but they are definetely higher than my dash vents. Here is two pictures of the back of the evap core, there was a fair amount of leaves on the resistor but almost none on the back of the core. The core looks pretty leafed up on the back but not really clogged, maybe im wrong. But what the hell is the point of this resistor? Like no plugs relative to ac are going into it, and the top 2 pins are corrided off so it wouldnt work anyways. Thanks, Andrew

ALSO i can see that the vaccum line im missing goes to that resevior so ill be sure to hook that back up!

 

The resistor gives you your different blower speeds. They mount it remotely from the speed switch in the airflow in the duct, because those little coils get red hot and the airflow from the fan keeps it cool. That is also why a lot of these trucks catch fire, those leaves get against the red hot resistor and then bad things happen.

You should be able to pull the blower motor out and get a view of the other side of the coil. Like was said, this is the side that clogs. And in my experience, the dirt and leaves get wet from the A/C sweating and it all turns to a hard mud. Some cleaner like fantastic or something like that works well to break it up. And then it hopefully runs out the drain if that is not clogged. That housing has a condensate drain at the bottom of it for the A/C to drip.

 

Hey Franklin, good to talk to you again

Just cleaned the back side of the evaporator core and all seems well there. I recognized that the cut vacuum line is the line that runs to the intake so we were having no vacuum there so i just lined it up and im going to try it. Like i said this resistor was never plugged in but the blower still changes speed, how can that be? Should i get a new resistor since mine is broken? And if so what lines go to it?

Like i said it changes speed (from 12v to 12.4) but i want to make sure thats the right voltage and all that enough to run the fan
'

 

I sure hope he has access to air, or he’d have already suffocated. I highly doubt he’d be posting about his truck while gasping to take his last breaths.

Or did you mean compressed air?

 

Alrighty so i am completely stumped on the wiring for the resistor/motor. I tested both ports on the blower plug and one im getting 12.4 and the other im getting 14v consistantly. I put everything back together and i am getting a little more airflow (my high is probably where a low should be) so im thinking it is wiring. Like i said the fan changes speed but it still barely blows air. Any ideas?

I am thinking the resistor but i have no idea where and how that wiring goes.

 

If this is the way it is wired and the speed changes then I would say its good. Think mine is the same.

Nice fire starter!

Yes pull the blower motor and dig out all the dirt & leaves.
I used "compressed air" to blow out what I could not dig out, it made a good mess!
When you install the motor back check the gasket between the motor & the housing.Mine leaked pretty good and has to use closed cell foam as a seal.

Vacuum should go from intake to a vacuum tree up on the fire wall then a hose to the can or ball on the inner fender.
There should be a check valve between the tree and the can / ball.
There is also a tee between the check and can / ball and the tee is supply vacuum to the HVAC that runs thru the fire wall to the have AC controls.
Sorry I dont have a good picture of my setup.
Dave ----

 

Yep that is how i lined my vacuum, or close to it. When i turn the ac on we have the switches working now. But like i said it is still blowing really slow. I cleaned it all out, im just gonna wire right to the battery and see what it feels like inside and then i can determine the wiring or not

 

Did you say it was blowing out the defrost pretty good but no where else?

If you have vacuum going to the HVAC controls if you move the lever from defrost to floor does it change to the floor?
You can also look at the vacuum motors when you move the lever to see if they move.

We are trying to see if
1 - the controls are working
2 - the vacuum motors are working
3 - if the known door inside has a broken hinge or not.

If you think maybe vacuum is not getting to the controls if you follow the lines in thru the fire wall you will find a plug on the inside with the 2 lines.
You can unplug it and see if you get vacuum at that point.
My system was work then stopped. I had vacuum in the engine bay but not at that plug. I traced it back after pulling out my hair that the plastic line broke right in the rubber fire wall pass thru.
I made a hole in the rubber and pushed a rubber hose thru to replace the broken line.

Also when I first got my truck running and checking the HVAC for the broken door hinge I found if I went right from any setting but off (I think it was) the system would not change fully to dash vents.
I had to go to off then to AC / vent for the vents to blow. I dont remember needing to do this lately so maybe it just needed to work some?

My control came from a member who picked it up from a junk yard so we did not know the story of it.
Dave ----

 

Yea sadly i dont know the story of mine either. I had no vacuum lines anywhere so i just lined the whole thing i can feel/hear stuff move and change speed when i move the lever but like i said my motor isnt strong enough to even hear a difference. I turned it to floor and the dash vents stopped but it was blowing so low i couldnt even find where it should be coming out. I wanna make sure the blower is doing its thing first then i can determine where the flow goes.

 

Okay here is the question i need answered. There is 2 wires to the blower motor, when i test with the voltmeter one is running 13-14 volts and changing when i flip the speed, and the other one is always reading 12. Where the hell is the ground????? Is the constant 12 shorting out somewhere????

 

You don't know the love some us have for our trucks.

My life be damned! Maggie lives on!