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  1. #1
    FEP Power Member Ourobos's Avatar
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    Default 86 HVAC blower only works on LOW

    HVAC blower only works on very low on my 86 SSP. I've replaced the resistor and the blower motor on the box. No change. Any ideas what to check next? My new compressor will be here tomorrow and would like to iron this out ASAP. THANKS
    1986 CHP SSP Coupe

  2. #2
    FEP Power Member Ourobos's Avatar
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    I have now put a new speed selector switch on the HVAC panel, not much change. Out of ideas. Anyone?
    1986 CHP SSP Coupe

  3. #3

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    Check the voltages at the fan connector.

  4. #4
    FEP Power Member dagenham's Avatar
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    Is there a dirty ground somewhere maybe?

  5. #5
    FEP Power Member Ourobos's Avatar
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    What am I looking for, 12v on high? What about low?

    It's an SSP, so it has MANY grounds, I don't think that's the problem, but who knows..
    1986 CHP SSP Coupe

  6. #6

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    Does it only run on the low speed and not run at all on 2,3,4? Or does it run slow on all speeds?
    84 LX Vert. 5.0 5speed canyon red on white
    99 cobra, electric green on medium parchment, vortech s-trim

  7. #7
    FEP Super Member erratic50's Avatar
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    Check the pinouts on the motor. Disconnect it and feed it power and ground directly and see how it acts that way. Pretty common for bearings to give out and it to run slow on all speeds. Real bugger to change too.

  8. #8
    FEP Power Member Ourobos's Avatar
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    Just put a new motor in Erratic50..

    It is on low at all times Lowetlx.. Once I put a selector switch on the panel, it almost seemed like I heard it change a LITTLE when I went from L to M to H.. But it may have been a placebo effect.. It's pretty much on low all times.. New selector switch, new resistor in the box, and new motor - to recap.

    I'll check voltages in just a few.
    1986 CHP SSP Coupe

  9. #9

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    Quote Originally Posted by Ourobos View Post
    What am I looking for, 12v on high? What about low?
    See:
    http://www.veryuseful.com/mustang/te...dy-Diagram.gif
    Diagram thanks to TMoss.


    Ford likes to switch ground.
    So, if I get this right :-), ...

    "Off": (The fan isn't really 100% off)
    Orange/Black: ~10v
    Light-Green/White: - Lower voltage than the Orange/Black wire.
    Yellow/Red: Lower voltage than the Orange/Black wire and the Light-Green/White wire.


    Low:
    Orange/Black: ?~7v?
    Light-Green/White: - Close/Same voltage as the Orange/Black wire.
    Yellow/Red: Lower voltage than the Orange/Black wire and the Light-Green/White wire.


    Medium:
    Orange/Black: ?~5v?
    Light-Green/White: - Close/Same voltage as the Orange/Black wire.
    Yellow/Red: Close/Same voltage as the Orange/Black wire.



    High:
    Orange/Black: ~0v
    Light-Green/White: - Close/Same voltage as the Orange/Black wire.
    Yellow/Red: Close/Same voltage as the Orange/Black wire.



    Do the tests above, note the voltages on the:
    a) Orange/Black wire,
    b) Light-Green/White wire,
    c) Yellow/Red wire, and the
    d) Black wire (should always be ground).

    Post the results.




    Good Luck.
    Last edited by stangPlus2Birds; 11-08-2017 at 04:48 AM.

  10. #10

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    Nice diagram and voltages. That Tmoss has our backs! I followed his porting instructions for a stock 5.0 lower and it made a difference you could feel. Let us know how you make out when you get it fixed.

    Mike
    1982 GT 351W, retro hyd roller, ported Pro Comp heads, Tremec, M2300K brake kit, Recaros...needs paint!
    1984 LX 5.0 Vert *SOLD*
    1993 Cobra #3971 mostly stock *SOLD*
    1966 FFR Cobra replica 383W, Vic Jr heads, Vortech YS, TFS Box intake, 652rwhp, crazy fast!
    1987 GT in MM&FF May of 97 "Not Fade Away" white and purple. Sold 1999

  11. #11
    FEP Power Member Ourobos's Avatar
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    Where exactly is the Lt. Green / White? I don't see it on the diagram, what circuit is it?

    Also, the Yellow / Red is off the switch in the dash I presume?

    I am getting 12v to the resistor on the Orange wire, regardless of fan selector speed. I can open the blend door by hand and see the fan come on with Low-1.. If I move up to 2, no change in it's speed. If I move up to 3 it increases slightly (still well below what it should be), and up to HIGH-4 no change from 3...

    One thing I do see, and this is the factory plug and hasn't changed, why does orange go to blue, and vise versa?

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    1986 CHP SSP Coupe

  12. #12

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    Does your blower motor plug directly into the resistor?
    84 LX Vert. 5.0 5speed canyon red on white
    99 cobra, electric green on medium parchment, vortech s-trim

  13. #13

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    My 84 SVO heater/ac unit only works on high...........ill be waiting to see the out come on this issue.

  14. #14
    FEP Power Member Ourobos's Avatar
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    Lowetlx - yes, that is directly into the resistor - new motor just like original.

    Chads84svo - that is TYPICALLY a sign of a bad resistor in the HVAC box
    1986 CHP SSP Coupe

  15. #15

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    Really?.....thanks bro....ill look into it.

  16. #16

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    Quote Originally Posted by Ourobos View Post
    Where exactly is the Lt. Green / White? I don't see it on the diagram, what circuit is it?

    Also, the Yellow / Red is off the switch in the dash I presume?

    I am getting 12v to the resistor on the Orange wire, regardless of fan selector speed. I can open the blend door by hand and see the fan come on with Low-1.. If I move up to 2, no change in it's speed. If I move up to 3 it increases slightly (still well below what it should be), and up to HIGH-4 no change from 3...

    One thing I do see, and this is the factory plug and hasn't changed, why does orange go to blue, and vise versa?
    The connector in your hand is the one that goes to the blower/fan from the 12v-power-from-the-switch.

    Fwiw, I had Three Ford Dealer manuals/books for Stang/T-Bird '86 wiring. They are all a little different. And, none, I repeat *none*, were within 50% of the wiring color codes on my main wiring harness for my '86 T-Bird. Battery corrosion ate through the loom and wires. What a PITA that was to fully back-track, and replace the effected wires.

    So, always take color-codes in diagrams "with a grain of salt". Also, like with the main wiring harness on my ''86 T-Bird, they make not even be correct to the wires, the number of wires, and where the wires go. Sorry, that's life with both Ford and GM cars (at least before 2010).


    So...
    That connector goes to the blower-motor? Which side is what? It looks correct. But, it is kinda bad that a wire is black. That black wire like goes to the fan speed selector?

    You need to look at the 4pin blower-resistor connector. Also, remove the resistor, and look at it.

    If the fan stays on low, then that sounds like a bad fan-speed switch.
    Typically, the resistor blows/melts, and the blower-motor only works on high. I'd say that's ~99% of the fan speed problems with fans that only have fixed speeds. The temperature controlled HVAC systems, typically use a "PWM" (pulse-width changes) to vary the fan speed.

    Look at the connector at the blower-resistor, and see if those voltages change.

    If you know how to use resistance measurement feature on the DVM, then
    a) Disconnect the blower-motor connector.
    b) Look at the resistance between
    1) The orange/black wire and the
    1a) Light-Green/White wire
    1b) Yellow-red Wire.



    Fan Speed Switch Operation:

    ***Resistance between the Orange/Black wire and the other wires.

    Off
    Light-Green/White wire - no
    Yellow-red wire - no
    Black wire - no


    Low:
    Light-Green/White wire - Yes
    Yellow-red wire - no
    Black wire - no


    Medium:
    Light-Green/White wire - no
    Yellow-red wire - Yes
    Black wire - no


    High:
    Light-Green/White wire - no
    Yellow-red wire - no
    Black wire - Yes


    .

  17. #17

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    Quote Originally Posted by chads84svo View Post
    My 84 SVO heater/ac unit only works on high...........ill be waiting to see the out come on this issue.
    Like Ourobos said:

    You need to look at the 4pin blower-resistor connector. Also, remove the resistor, and look at it.

    Typically, the resistor blows/melts, and the blower-motor only works on high. I'd say that's ~99% of the fan speed problems with fans that only have fixed speeds.

    Good luck!

  18. #18

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    Any pics of the resister? Not sure its location and what it looks like.........is it easy to change once the control unit is removed from the dash?

  19. #19

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    Pm me with your info I can text you a wiring diagram. The diagrams above don’t look right. The best way is to do a voltage drop with the fan running to see where the resistance is. Being that it is affecting all speeds it’s probably between the fuse and the resistor or from the control head to ground.
    84 LX Vert. 5.0 5speed canyon red on white
    99 cobra, electric green on medium parchment, vortech s-trim

  20. #20
    FEP Senior Member liv2roc's Avatar
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    I had this problem. mine was the resistor. I would change it again maybe you got a bad new one.

  21. #21

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    I think you need to stop replacing parts and diagnose the problem. This really should not be that difficult.

    The main thing to keep in mind about the fan circuit is, with factory A/C, you could remove the blower switch
    entirely, and the fan would still run on low, as long as the HVAC selector switch is anywhere except off. The
    way this works is, there are several segments in the blower resistor, that are all in series in the path between
    the blower motor and ground. The fan switch selectively bypasses those segments to raise the fan speed.

    So the fact that the blower runs on low, pretty much says the resistor assembly is fine. Actually, it says quite
    a bit more is fine. Here's a less confusing diagram of the circult - (This is for cars originally equipped with A/C)

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    Now, I'm a bit confused about the description above that says your fan is plugged directly into the resistor block.
    That suggests your car was equipped with only a heater, or you have dealer-added A/C. The blower wiring for that
    setup would be quite a bit different. For one, the fan switch on that version switches the ground to various points
    in the resistor block, so that it can turn the fan off entirely.

    Name:  078 Heater.jpg
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    Last edited by JACook; 11-15-2017 at 11:16 PM.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  22. #22
    FEP Power Member Ourobos's Avatar
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    I had thought the motor was wired and running backwards, I briefly reversed the wires to verify that wasn't true, now the motor won't even come on. Fuses are good. I may have fried it. Although I'd think it would just run backwards if reversed. Anyways, it's wired the way it was but now I'm even deep in. I'll get to it later on and update.
    1986 CHP SSP Coupe

  23. #23

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    The motor can run either direction without damage, and being a centrifugal device, it would still drive air out
    the vents. But the blower wheel is quite a bit more efficient when it's spun in the intended direction.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  24. #24
    FEP Power Member Ourobos's Avatar
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    ^ lol RIGHT.. That was my hope was that it had low output due to being wired in reverse.. No such luck. Will follow your diagrams when I get some free time and report back. Thanks again
    1986 CHP SSP Coupe

  25. #25
    FEP Power Member Ourobos's Avatar
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    Wanted to report back with the solution.. On the back of the HVAC panel, the main OR/BL wire that controls speed wasn't seated inside the plug properly. I replaced all that so it works on all four speeds now. It's these odd ball ones that get me as usual. Now time to charge this AC up, thanks again.
    1986 CHP SSP Coupe

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