A/C Stuck on defrost vents - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 12-12-2007
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A/C Stuck on defrost vents

My a/c (and heat) only blows out the defroster vents no matter what setting I have it on. Is this something I could fix with knowing little about the a/c? If so how can I fix it?


Also the only steed setting that works is high, I have taken the hvac panel apart and took apart the **** that controls the speed (cant think of the name right now) and cleaned it up and it should work fine. I checked the voltage on the wires connecting to the switch and only one had power. What could be causing this? Does any body have a wiring diagram?

Its been like this since summer and im tired of my windows fogging up to where I cant see.


Edit: sometimes when I start the truck or stop at a light it will start blowing out the front vents until I press the gas and start driving.
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Old 12-12-2007
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Defrost only - You have lost some or all vacuum to the A/C controls. Check the vac reservoir for cracks or disconnected vac lines - later Rangers have the vac reservoir under the engine air filter box but I think it is behind the fender on the passenger side of your 98.

Then trace the vac lines in both directions from the reservoir looking for problems. They sometimes get disconnected during a plug service or melt on the PS exhaust manifold. Your Pulse Vacuum Hublock system uses the same vac reservoir, so a major leak in the PVH system can affect the A/C also.

The single speed on the blower is probably due to a failed resistor block near the blower. It is a $15 part.
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Old 12-12-2007
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I had to replace the hubs because of vacuum leaks and I plugged one by the hub because the rubber line had split but I left the other side alone so that may be a problem there. Ill check that out.

I think the vacuum reservoir is behind the fender but do I have to take off the fender to get to it? Ill have to look at it tomorrow to see if I can find another way.


What does this resistor block look like?
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Old 12-12-2007
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I think that you should be able to get to the reservoir by removing a few of the fasteners on the plastic inner fender and flexing it out of the way.

The resistor block is a small rectangle held in by 2 screws. It has an electrical connector going to it and it is next to the blower motor in the HVAC plenum on the PS firewall. When removed it looks something like the picture below. The resistance coils are hidden inside the plenum when the block is in the installed position. The coils eventually get brittle and break - that's what makes the lower speed modes of the blower fail.

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Old 12-12-2007
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Ok, thanks for the info.

Im going to check over all this tomorrow after school and ill post back with what I find.
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Old 12-12-2007
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The vacuum ball is behind the fender. When I had this happen on my truck one of the plugs on the hub block had fallen off. Its sitting next to the radiator on the frame rail on the passenger side.... just something else to look for.
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Old 12-12-2007
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I couldnt help but to go work on it after I made that last post about working on it tomorrow lol.





rngprerunner I checked that wile tracing the lines and it looked all ok, I did cap off the other vac line going to the pass. side hub tho so that should rule out anything to do with the hubs.



rwenzing I checked all the vac lines and the reservoir behind the fender and it looks all good. I also disconnected the vac lines in several places to make sure there was a vacuum and there was even under the dash.


I couldnt find the resistor block but I think I found something that looks like it may be it. If it is it then how am I going to get that off? lol its so tight up under the dash I dont know if I can get to it with out removing everything....

Here are some very bad pics of what I think it may be.

Is that it?


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Old 12-12-2007
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The resistor block in under the hood. Look near the passenger inner fender where it meets with the fire wall, there is your heater box. On the forward face of it will be the blower motor and the resistor. Look lower and a little more inboard of the motor to find the resistor. It will have 2 ~10mm screws holding it in and ~6 wires running to it, and they will be fairly heavy gauge wires also. The curly Q's shown in the picture above are actually inside the heater box so you cannot see them until you remove it.


On the loss of vacuum, I had a line touch onto the header and it melted it just enough to close it off inside, that had the same effect. However, if your getting vacuum inside the cab of the truck this is probably not your issue
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Old 12-13-2007
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Having some vacuum under the dash does not necessarily eliminate the possibility that there could be a vacuum leak or restriction somewhere in the system. The vacuum must be sufficient to operate the 3 vacuum servos under the dash that direct the airflow. Recheck for disconnected, pinched, melted or otherwise damaged hoses under the hood. Look for same under the dash at the HVAC control panel and at the 3 servos.

As stated above, the blower resistor block is in the plenum next to the blower assembly. This is under the hood in the passenger side firewall area, not in the interior.

At the center of this picture is the Explorer EATC fan speed control module. Your Ranger's resistor block looks a little different but it is in exactly the same location.

Purloined from J. Griggs's CarDomain:
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Old 12-13-2007
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ok, thanks alot guys I got confused and thought it was in side the cab.


I just reread my last post and it looks like I forgot to add to it that under the dash has some vacuum in the lines but not as much as under the hood.

Ill recheck all the lines, and check that resistor block.
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Old 12-13-2007
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Icon14

ok, I got the resistor block out and spend a hour just trying to get it unplugged. It was rusted on and full of mud, but when I finally did get it off one of the prongs had broke or rusted off in side the plug and it also looked like it shorted out because the plug on the harness is melted. I think ill just cut off the melted plug and crimp some terminals on the ends to connect up the new one.


I found the vacuum leak also, It was where a vacuum line entered reservoir behind the fender and where the same line connected to a T and branched off to other lines. It had some rubber vacuum hose that was used to couple the line to the reservoir and the T and they were beginning to rot and had small splits in them. I replaced those peaces with some I had laying around and now the air blows out the front vents and floor like normal.

I went to every auto store in town and non had the resistor block so I had to go to the dealer and order it ($24.40). Should be in tomorrow at 8:00am so ill pick it up and put it in after school. Ill report back with if it fixes the speed problem (it should).
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Old 12-13-2007
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Good to hear you found the vacuum leak. A lot of times they can be hard to track down.
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Old 12-13-2007
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yea I'm glad I found it, now I dont have to deal with a fogged up windshield every time I drive my truck. I also forgot how cold my air blew. lol
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Old 12-14-2007
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IT WORKS!!

I installed the part and it works like it should now.

Thanks a lot for the help guys, I just want to set in my truck now with the air blowing on me. lol
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