I just bought a '98 Ranger 2wd with a 2.5L(?) 4-cyl (two plugs per chamber). It doesn't have power anything, fiberglass bed, bed liner, and a 5-speed. I don't think it's an XL or XLT (maybe Splash?). Anyway, Everything works except for the heater temperature controll. It's always on hot. The an blows good on all of the heat/vent/AC/MAX AC/Mix and in all of the right places. The only problem is it's always blowing hot air.

I found that there is a vacuum actuated heater core bypass valve that closes off the hot water to the heater core. For some reason, no matter what setting I put the heat control at, there is no vacuum and therefore water always flows through. When I shut the engine/key off, it gets vacuum and shuts off the heater core. As soon as I start it back up, the vacuum disappears and it blows hot. I'm thinking that maybe the **** itself (potentiometer) is bad and am thinking of replacing that, but Ford wants $25 for the thing and I don't want to just start throwing money at the problem. I want to know what I need to replace before I replace it.

The PO had a replacement valve in the glove box when I bought it, so I installed and tested the unit (works perfectly). However, there is no vacuum signal when it needs it.

Where else should I look? What controls the vacuum signal to this bypass valve? Is this a common thing, and if so, what is usually the culprit?

What should be the resistance range of the **** unit? What should it be at full clockwise and full counterclockwise, measuring from the center pin to the two outside pins?

Once I find the resistance, I can get a cheap potentiometer that matches the resistance and spend $0.50 instead of $25...

 

Definitely the blend door or BDA.

See: http://www.blenddoorfix.netfirms.com/

 

That doesn't make any sense at all. Why would they leave the hot water flowing through the heater core when the **** is in the cold position? Isn't that the purpose of having a vacuum-actuated bypass valve, so when it's set to cold it won't have to worry about blowing past a hot heater core?? And wouldn't it be much simpler to just shut off the water instead of making a big, complex air mixing plenum with multiple "valves" and electronically-controlled doors????

I'll look at the blend door problem, but I don't think that's it...

 

I didn't design it, I'm just telling you how it is.



As noted in the other thread, the heater control valve is open all of the time except when OFF or MAX A/C is selected. That's why you are getting hot air all the time (and because the blend door is stuck in the "warm" position).

If you're not getting cold air at MAX A/C then your A/C system probably needs a charge.

 

Hmm. That's dumber than ****. My dad's '69 Ford F250 has cable-controlled heating and has never had any trouble with this kind of thing. Yet another example of "efficiency in simplicity."

I guess I might've sounded kind of like an a-hole. My comment wasn't directed at you, but at the engineers that keep making stuff just to keep their job (not necessarily to make anything "better"). Sorry for that.

You're right; Max A/C works beautifully. I just assumed they would turn off the heater core when it's in any of the cooling positions. Thanks for your help and hopefully it's simply the blend door.

 

No sweat, you didn't come across as a jerk, just a frustrated Ranger owner with a blend door problem.

Good luck with the repair.

 

Rockledge,

Thanks for posting the link to the blend door fix. I have a 1998 ranger and it had a blend door problem. I used the information from that link and repaired the door last night. Everything works fine now.

mtpocket

 

Well, one reason to have full time flow through the heater core is to avoid sedimentation and corrosion. If it were blocked off to coolant flow for months at a time you can imagine what you'd get when you needed heat.
Several FoMoCo vehicles require that you remove the dashboard and discharge the A/C system to replace a corroded heater core. I know that put a lot of Taurus/Sables, and probably Explorers in the boneyard as they weren't worth the repair cost, just like the mode control motor failures and blend door breakage...
Keeping the coolant flowing will reduce the likelihood that you have to replace the heater core. Speaking as a home-grown self ejumucated Enjineeer. heh.
tom