I've got a weird one here.

I have a 2008 Ranger Sport 4x4, new to me, 150K miles. When I bought it the blower didn't work. No big deal I figured. The owner told me about it and said his buddy had fixed it, but it wasn't working again.

I checked the resistor - it was obviously new and recently replaced. Same with the pig tail, which appeared to have been installed properly. It wasn't a hack job is my point. I checked the fuse under the hood, which checked out. Then the fuse in the passenger side interior. I found a blown 10A fuse.

When I replaced it, the blower fired up and works at all speeds. Sweet! But as soon as I change the vent to anything other than the upper (IE: AC, MAX AC, upper and feet, feet only and defrost) the fuse instantly pops.

I can switch between OFF and UPPER at all speeds with no problem. But any other location will blow the fuse. It blows if I start the truck in any of those spots, and blows if I use the switch to change from upper to something else.



I don't understand how the blend door system works, any advice here? Is the upper kinda like the 'standard' position for the blend door, and when I try to get it to do some work it blows? Any advice is appreciated, I'm not sure where to start here.

 

Blower motor uses a 30amp fuse, so blower motor fuse is not blowing

Whats the fuse #

You can get your owners manual here : https://www.ranger-forums.com/genera...1-models-3747/

Look up what that fuse is for, let us know

Blend door is electric and is for HEAT control so isn't a Vent
It "blends" warm and cold air by opening and closing off heater core air flow

Vents are usually vacuum controlled, use "vacuum motors", so not electrical
You could have a vacuum motor that is shorting out a wire near it when it opens a vent.

Defrost is the default setting, so all vents are closed when air is coming out the defrost vents

 

Ah interesting, thanks for clarifying.

It is fuse #27, 10amp fuse. My manual calls it the "Climate control blower relay/blend doors".

So any time I try to change to a door other than the upper vents, it blows.

 

Ok so I unplugged the AC compressor and now my fan works regardless of the switch position. I did notice that when I change the dial to the foot position it just blows out the defrost. Is that because the compressor needs to be running in order to change the vent position?




What does this indicate? A bad compressor, or perhaps a short? Any suggestions for next testing steps?




Can I run it with the compressor not attached for now?

 

This 2010 looks like correct diagram then

The Blend door doesn't look like the problem since it gets power from fuse 27 when key is on, so if it was shorted then fuse would blow instantly
The COLD/HOT **** adjusts the Blend Door motor not the vent ****, they just share the same fuse

Find and pull out the Blower Motor Relay, says its in Engine fuse box in diagram but in 2008 it could be in cab fuse panel
In any case find it and pull it out

Put in a new fuse and turn on the key
Now turn the Vent control **** and see if fuse blows
If fuse blows then problem is IN the panel/****
If fuse doesn't blow replace Blower Relay

 

This is a more detailed diagram that includes the AC system

There is no electrical or other connection between AC compressor and Cab vent ****
AC compressor is activated by a relay via the computer
Computer is "asked" to start AC by your selection, it will then activate Relay.

The fuse 27 power does pass thru AC high and low pressure switches and then to computer

The vents are control be engine vacuum, so engine must be running or just shut off for vents to hold or change positions
Unplugged AC compressor won't effect vents

 

Jut gave it a try. With the relay out the fuse did not blow.

The blower also didn't run but I assume that's because the relay was not installed. So does that indicate a bad relay?

 

And if the relay is bad, why does unplugging the compressor affect my ability to activate the blower in all the vent positions?

 

I replaced the relay and everything works now!! Only issue is that setting the vents to the floorboards still sends air to the defrost

 

Good work, and you may have a vacuum issue

All the vent doors are opened or closed by vacuum, so air direction/flow is strictly vacuum powered

Diagram here: https://www.ford-trucks.com/forums/a...ntid=517&stc=1

The top part is in the engine bay, i.e. the check valve and Vacuum Reservoir

There are 4 vacuum motors, their doors have V and NV for vacuum or no vacuum for that position
When you select a Vent position you are sending vacuum to a door(V position) and stopping vacuum at another door(NV position).

Defrost, as said, is NV at all doors, so if there is a vacuum leak or no vacuum from engine bay line, the Defrost is all you get.

When the vacuum reservoir has a leak then when you accelerate the vents change to defrost, NV, because there is no reserve vacuum to hold doors in position, and there is no engine vacuum when accelerating

 

Well unfortunetly it looks like my fuse issue has come back. I had no issues for a couple days but yesterday it popped again as soon as I went to set the vent to the first position to the right of OFF, which is dash vent and floor boards.

Last time when I pulled the blower relay, I wouldn't pop a fuse. So I tried that again, but this time the fuse DID pop.

I had also had success by unplugging the AC compressor clutch, so I did that, fuse popped again.

So I unplugged the ac clutch, took out the relay, and unplugged the pigtail at the back of the compressor too. Nothing blew at this point, so I started putting the stuff back together. Then my blower worked again!???

So I left the engine running and wiggled all the connections, shook the wiring harness, tapped on the fuse box, relay, dash controls, everything I could think of to make a short rear its head. Nothing happened, it just kept working.

I came back an hour later and went on a drive. A few minutes in I switch on the floor board vents and POP.

What is going on?? I've tried to isolate the blower circuit, the AC compressor and clutch circut, the relay, sometimes a test comes back as bad, then the next time as good, and so on.

Since I've blown a fuse now with the ac compressor disconnected, and I've also blown a fuse with the blower relay disconnected, does that narrow it down to the dash switch, or some bad wiring between the switch and the vent doors?

 

AC compressor has nothing to do with fuse 27

Fuse 27 only powers the Climate control switch and Blend door, but......

It does send power thru the two pressure switches for AC

That may be the "pig tail" you are referring to, there should be two of them, low pressure and high pressure, first switch should have a Green/orange stripe wire and Yellow wire

Fuse 27---Climate switch--------(Green/orange stripe wire)------high pressure switch-----(yellow wire)---------low pressure switch---------(green/blue stripe)--------Computer

So........one of these pressure switches could have a short, find the high pressure switch and unplug its wires, that removes the low pressure and computer from the circuit
AC won't work.

High pressure switch is usually on passenger side AC line

 

The high pressure switch is one of the things I disconnected but still blew the fuse. That sits at the back of the compressor, right? I tried disconnected the ac clutch, high pressure switch, and blower relay all individually, each time the fuse blew.

I'll find that low pressure switch and see what happens. I believe that sits right by the blower motor.

Though if Im' understanding you correctly, having unplugged the high pressure switch, that'd eliminate the lower switch automatically? Is that correct?

I don't think it's the blend door as I get hot and cool air out the vents when i'm in the dash vent position.

Am I correct that the AC would not come on for the dash + floorboard position? And if so, the fact that the fuse blows in that position, would that not indicate this issue has nothing to do with the AC system?

 

Just went out and disconnected both pressure switches, low and behold the fan works again. I was down to my last fuse, so I didn't try plugging them in one at a time to see which one pops, but based on what happened earlier (I never disconnected the passenger-side high pressure switch) I'd assume it's the high pressure.

I'm going to leave them both unplugged for a day while I drive around and see if it continues to work... just because some of my earlier tests suggested one thing only to result in another. I'll pick up more fuses and start testing the high pressure switch circuit for a short.

As always, thank you for your help!

 

Sounds like a plan

 

It's been a few days and maybe a dozen trips since I unplugged the pressure switches, no blown fuses. I plugged the switch by the blower back in part way with no ill effects. So it looks like I've finally pinpointed the issue to the switch and/or harness for the pressure switch behind the AC compressor. Time to start testing some wires.

Do the switches themselves go bad? And if so, do they go bad in a way that results in a short?

 

Good news

The Pressure switches are Normally Closed, so with an OHM meter from one switch terminal to the other there should be 0 OHMs
And test each terminal for 0 OHMs to ground, which would be a Short, bad thing
Also test each wire for 0 OHMs to Ground which would be a short on that wire

The fuse 27 12volts comes from the Control switch in the cab on the Green/Orange stripe wire to that the FIRST pressure switch in the chain
The 12volts passes thru that first switch to the next switch(yellow wire) and then thru the second switch and out to the Computer on a Green/Blue stripe wire
When computer sees 12 volts on that wire it activates the AC clutch relay

 

Tested the wires at the plug. You are correct! The yellow wire reads 0 ohms when I put one lead on that wire and another to ground.

So I'm assuming this wire runs through the harness to one of those big multi-wire connects at the back of the engine bay, where it connects to the dash and instrument panels. if so, I'll remove the wire there, and test for a short. If that looks good, then I'll replace the wire to the connector. If not, then I guess the short must be behind the instrument panel somewhere. Glad I know what it is at least.


If the short IS in the wiring harness under the hood, do you guys actually unwrap that entire harness to replace the wire, and re-wrap the whole thing? I was thinking I'd source some good quality wire and run it along the outside of the engine bay within it's own protective housing, then to the plug. Much less work.

 

One more thing I'd like to test before going to buck wild in that harness is the switch itself. After some Googling, I found a few other people with identical issues to me, and the switch was at fault.


Am I able to remove this switch without depressurizing the AC system? I think there is a schrader valve behind it, but not totally sure. The new switch is $60 here, so I'd like to test it before throwing money around.

 

Nevermind I realize instructions for testing the switch, as well as the harness, were both provided by RonD a few posts back, doh! I'll go back outside and fire up the multimeter...

 

Pulled back the housing and found the green wire with orange stripe has what might be two repairs. It looks like heat shrink to me with a br of glue or something sticking out the ends.. I know something around here has an inline diode, and I don't know what they look look, but this looks like a bad repair job. Thoughts? Is something supposed to be on this wire, or no?

 

Here's a photo

 

The Yellow wire runs between the two switches, not to dash or computer

You have to drain the coolant(freon) to replace a pressure switch

On my diagram
Vent switch------(green/orange wire)------------switch------(yellow wire)------switch-----(green/blue wire)---------computer

Those are repairs on the green wire with orange stripe, that's the wire that runs to the vent control on the dash
No diodes on wires, there is one in the cab fuse box, but not really part of AC system, it is for PCM

Yes, rather than pulling wiring harness apart you run another wire of the same gauge to replace a shorted wire, BUT...............you must FIND BOTH ENDS of that wire FIRST, and have BOTH ends disconnected, then test wire for short to ground, if still shorted then run the new wire
If short is gone then DEVICE at one end of the wire has the short not the wire

 

Where is the computer that the last switch is connected to, the wire with the repairs I talked about? I'm not sure where that wire goes to.

My AC is working now but I didn't do anything hah. Just pulled a few connectors to check for a short. But I couldn't find where that last green wire with orange stripe, the one that goes to computer, I can't see where it actually goes.

And in the process I looked at my fuse box and managed to bump the inertia switch, the connector snapped at the switch haha. So I've jumped the wires together so my fuel pump works until I can get a new connector.

 

Alright so I see the computer is where all the wires seem to be heading to at the back of the engine bay. Right now everything is testing out properly and no surprise the AC is working fine and no fuse is blowing. I haven't done anything though so I need the short to happen and stay that way to really figure it where it is. Frustrating!

The shoddy repair near my high pressure switch seems an obvious spot, but if the wire was broken in there I'd think it would just cut out, not actually blow a fuse right?

I'm not really sure what to do next here.