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Heater valve issue? How does it work?

Discussion in 'Stock 1995 - 2001 Explorers' started by lobo411, October 11, 2013.

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    1. lobo411

      lobo411 Active Member

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      Hi all,
      96 Explorer 4.0 w/ manual temp control. I've had a very occasional issue (occasional in part because I live in SoCA and rarely use the heater) with the heat being non-functional. Usually it works fine, but occasionally it will come on only after I play with the heater control knob. However, I haven't been able to establish whether this is a coincidence or not.

      I also have an issue where on any 70+ degree day, my vents (ie temp control set to vent air from the outside) will start to deliver warm air. Sometimes it gets warm enough that I turn on the a/c just to cool down the vents, and then I have to repeat the process every 10 mins or so.

      I read through the forum and decided it might be the blend door, so I pulled the actuator but it works fine. The blend doors do make a bit of a "clump" sound when the actuator reaches the end of its transit at the "heat" side.

      Then I decided to test the heater valve. I turned on the car and had my mom turn the temp control knob from cold to hot, wait 5 seconds, and go back again. I expected to see the metal/plastic arm on the bottom of the valve extend/retract, but nothing happened. The vents delivered cold-cold to blazing-hot air, but I didn't see anything happen to the valve.

      Finally, I decided to unplug the vacuum line from the heater valve to check for vacuum. No discernible vacuum from my informal test.

      So my questions:
      1. How much vacuum should there be at the heater valve? Should I be able to feel it on my skin?

      2. What does the vacuum do? IE, when the temp knob is in the cold position, then the valve ought to close, keeping hot coolant out of the heater core. Does the vacuum *hold the valve closed* or does it *hold it open?*

      3. Any possibility this is the cause of my hot duct issue? IE, maybe the heater valve is letting some hot coolant into the heater core all the time, and that's why my vents seem to warm up while driving?

      I should mention that I've also had a recent issue where the car isn't getting to normal temp...just about 1/3 of the way. It runs fine and I get 20 MPG, but it never seems to get to normal. It has a couple of new hoses and a new radiator cap, and there's no air in the system. Could this be due to the heater valve, maybe keeping things a bit too cool by having an extra radiator in the mix (the heater core)?
       
      Last edited: October 11, 2013
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    3. koda2000

      koda2000 Explorer Addict

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      when running, the engine creates vacuum. usually around 19-20 PSI. there is a plastic line which is connected to the intake manifold on one end and to a vacuum ball/reservoir on the other. the ball/reservoir the is located in the front of the passenger side inner fender. from there, vacuum lines run to the HVAC controls. when you turn up the TEMP control, vacuum is sent to the heater control valve, which is then opened allowing hot water to flow through the heater core.

      the vacuum line to the heater control valve is tiny. without some sort of vacuum gauge you would be hard-pressed to feel any vacuum there. it should also be noted that, on a 18 year old vehicle, vacuum leaks are common. even a small leak would be enough to adversely effect any vacuum controlled device.

      the best way to test the heater control valve would be with a hand-operated vacuum pump with a gauge. if the valve works properly with vacuum applied, you need to start looking for a vacuum leak somewhere (anywhere) in the system. while the hard plastic lines can become cracked/melted, it's usually the rubber unions that dry out and become loose or cracked.
       
    4. Maniak

      Maniak Moderator-Stock 91-94 Staff Member Moderator Elite Explorer

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      Just to clarify, vacuum is measured in inches-HG, not PSI..

      Also, IIRC there is a 1 way check valve between the vacuum ball and the engine so when you lose engine vacuum due to high engine load you don't lose the vacuum in the ball right away.

      Otherwise, everything Koda2000 said is right on.

      ~Mark
       
    5. koda2000

      koda2000 Explorer Addict

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      my bad. i meant to say HG.
       
    6. lobo411

      lobo411 Active Member

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      Thanks for the info! I'll check if I have a vacuum gauge kit (inherited my dad's tools), but I'll probably end up just ordering it (there's such a thing as having too many tools...so many that you can't find anything when you need it!). That should help me figure out a lot of issues that I'm thinking could be vacuum related:

      1. The possibility that the EGR is only marginally operational, causing my high NOX emissions.

      2. The possibility that my heater valve isn't working correctly. Could someone tell me if it's possible to actually see the heater valve operate? Just by looking at the exterior design, it looks like the little arm at the bottom moves when vacuum is applied, but I'm just guessing.

      3. It looks like something isn't working right with my PCV valve--I had lots of oil built up around the PCV valve grommet, but also oil built up on the upper intake manifold to break booster vacuum line. Thought that was pretty weird.

      4. I thought I had an exhaust leak, but I guess it must be knocking/pinging? Makes a sound like someone sticking a piece of paper in a fan blade when I'm heavy on the gas getting over a big grade. Could it be running lean due to a vacuum leak (and the lean condition causing high NOX?)?

      Bleh...Where's cash for clunkers when you need it! ;) The car is actually really nice and clean, but IME there are two kinds of problems that spell futility: vacuum and electrical.
       
    7. koda2000

      koda2000 Explorer Addict

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      i believe you can actually see the linkage on the heater control valve move from the right angle. BTW, that's usually where they start leaking coolant from.
       
    8. lobo411

      lobo411 Active Member

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      OK, so I read somewhere in a different thread that when the system is set to OFF, maximum vacuum is directed to the heater valve. I started up the car and switched the selector to OFF, and sure enough, the heater valve closed up like a clam (pretty good amount of travel too...the plastic "pusher" that connects the vacuum motor to the actual water valve moved up/in like 1/2 or 3/4"). I pulled off the vacuum line and it immediately moved back to fully down/out. I could definitely feel the vacuum with my finger.

      I replaced the vacuum line and set the selector to VENT, A/C, and every other setting, plus of course cold/hot. Nothing I did resulted in vacuum being delivered to the heater valve, and the valve did not operate/move on any setting.

      Is this normal? Does the valve only shut when the system is off, or is it supposed to open and shut based on the temperature setting? Right now, it seems like it's always open and allowing hot coolant into the heater core, and that doesn't seem right to me. I'm wondering if this is why it's always a bit warm in my explorer even on nice days--if the heater core is always full of hot coolant, then just the ambient temp is going to be higher than it ought to be.
       
    9. SoNic67

      SoNic67 Well-Known Member

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      That's correct. I think mine it will shut off only on 'Max A/C'.
      The blend door is the temperature regulator. Probably the plastic socket (where the motor shaft goes in) is broken.
       
    10. Maniak

      Maniak Moderator-Stock 91-94 Staff Member Moderator Elite Explorer

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      AFAIK, it's supposed to close off the heater core in "off" and Max A/C settings only. All the others let the hot water into the heater.

      I'm only 90% sure of that though for your year (that's right for retrofitting the heater control valve on 1st gens). If that isn't right for your year then the Heat/AC head is bad as that is what controls when vacuum gets sent to the heater control valve.

      ~Mark
       
    11. lobo411

      lobo411 Active Member

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      Thanks very much, guys! Sounds like the heater valve is functioning normally, and the blend door actuator is working right now (I suppose it's possible that there's an intermittent issue with the actuator, but I operated it without the blend door several times and it worked perfectly). Since I use the heat only rarely, the problem is only intermittent, and I'm reluctant to go chopping into the plastic, I think I'll wait and see for now. Thanks all!
       
    12. ExporerDan

      ExporerDan New Member

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      Hi Lobo411,

      I think I have the exact same problem with my 98 Exp as you. Did you ever get it fixed?
      My coolant control valve works fine - I proved it by applying vacuum by turning the heater & a/c off, which shuts hot coolant flow off. But when the a/c is on in ANY position, vacuum to the valve is off and I get FULL HEAT all the time, even with temperature control set to coldest. The a/c compressor will come on as it's supposed to but, of course, it can't compete with the heater and it just blows HOT air all the time. As far as I can tell, the bill will be very high if someone has to remove the entire dash to be able to replace the control panel. So when I need a/c, I first start the engine and have the a/c off which applies vacuum and closes the coolant valve. Then I have a short flexible tube I added in line with the coolant valve vacuum line which I pinch off with a clamp, which maintains the vacuum. Then I can use the a/c. Of course, there's no temperature control - it's always FULL COLD but it's fairly easy to regulate with the fan speed and by where you direct the vents.
      Anyway, from what others have commented, it sounds like it's likely the blend door actuator. Was that the offender in your case?
       
    13. lobo411

      lobo411 Active Member

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      Yep, I fixed it--it was the blend door itself, not the actuator. The plastic shaft that the actuator fits into split and that was what was causing the intermittent problem. I guess sometimes it would slip in and work fine, and sometimes it would slip out and not work at all.

      I bought this part on Amazon: http://www.amazon.com/gp/product/B001SGIACU

      It's actually a revision kit that's designed for people to remove the dash and put the moving parts into a metal rather than plastic frame, which is more durable. However, I didn't want to tear up the dash, so I just threw away the hardware, cut a hole in the plastic beneath the blend door as described in parts of the thread linked below, and muscled the door in. It wasn't as easy as the thread makes it sound. There's a small 3/8" round area visible from below where the bottom end of the door pivots. I had to cut the bottom plastic enough so that the door could be wedged out, then wedge the new door in, and then epoxy the plastic back together again. Then I sealed the bottom up with epoxy and metal HVAC tape (from Home Depot), and it works good as new.

      Check the actuator first because you have to remove it anyway to fix the door.

      It was an annoying job to have to do, and I think it would be just that much more painful if you have big hands. So maybe bribe someone with small hands to do the job. Took me about an hour, with a lot of that being me standing there going "how the fudge am I supposed to get this door in the pivot hole?"

      http://www.explorerforum.com/forums/showthread.php?t=183742
       

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