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  1. #1

    Post HVAC Controls - Year-to-Year Differences?

    I've been learning a lot more about HVAC controls lately than I ever thought I wanted
    to know. When the contol panel on my '85 T-Top car fell apart, I started looking around
    for a replacement. Those that have done this know it's not always a simple task.

    Here is a list of the differences, as much as I know right now. I have grouped them
    into four basic versions, though there could be more that I'm not aware of. Note that
    these are all for cars with factory air conditioning. The panels for cars with heaters,
    or dealer-installed air conditioning, are completely different.

    I would appreciate if anyone can help fill in the blanks.

    First version, 1978-1980
    The most visible difference with these units are the two illumination bulb holes between
    the fan switch and rear defog or de-ice switch, if equipped. The upper of these two bulb
    holes is for the de-ice or defog indicator, which is separate from the switch. The lower
    of these holes illuminates the fan switch. The de-ice/defog switch lettering did not get
    any backlighting. The de-ice switch is a center-detent momentary contact switch, that
    connects to a timed relay above the glovebox, which supplies current to the grid wires
    on the inside of the back glass. The de-ice switch may also be labeled R.DEF. The defog
    switch, if equipped, is a 3-position Off-Low-High switch. The rear defog option consists
    of a blower unit with an electric heating element, that mounts in the rear package tray.
    This version of the control panel also has an additional vacuum control that the '83 and
    later panels don't have, that cuts vacuum to the heater core restrictor door when the
    temp slider is all the way at the "cold" setting. The selector, temp, and fan switch levers
    are about 1/8" longer than the earlier years. The later fan switch will fit, but the knob
    won't stick out as far as the others. Backlighting on this panel is blue.

    Second version, 1981-1982 (?)
    These have a single illumination bulb hole between the blower and defrost switches.
    The rear defrost indicator is relocated to the tip of the defrost switch knob. The defrost
    switch is larger, and now contains the timing function. The separate timed relay over the
    glovebox is eliminated. The rear defog blower option is also eliminated. Pictograms appear
    for the fan and defrost legends. The selector, temp, and fan switch levers are shortened
    about 1/8". The earlier fan switch will fit, but the knob will stick out farther than the rest
    of the levers. As near as I can tell, the heater core restrictor door function was eliminated
    in the HVAC box for 1982, replaced by a redesigned blend door, but the control panel still
    had the vacuum ports for it. Backlighting is still blue.

    Third version, 1983 (?) -mid 1985
    Looks identical to the second version, except the backlighting is red. Second and third
    version faceplates can be swapped to change the backlight color, and also to add/delete
    the rear defrost switch. (Involves re-melting or gluing the posts.) The heater restrictor
    door function is eliminated from the control panel.

    Final version, mid 1985-1986
    "Heat" and "Hi-Lo" functions are replaced with "Mix" and "Floor", which apart from having
    the positions swapped, and names changed, have slightly different functions. "Heat and
    "Floor" do exactly the same thing. "Mix" sends air to the floor and defrost vents, while
    "Hi-Lo" sends air to the floor and A/C register vents. "Mix" also engages the compressor
    clutch, while "Hi-Lo" does not.

    I have also discovered the heater box end of the heater cable changed sometime
    between 1984 and 1985. The early cable has the same style housing clips at both
    ends. The later one has a round housing clip at the air box end.
    Last edited by JACook; 04-19-2010 at 03:32 PM. Reason: Minor Updates...
    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

  2. #2

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    The heater control cable changed between 84 and 85.

    I have an 84 heater box in my car and had to use the 84 control cable instead of the 85 control cable since the mount on the heater box is different like you said.

    -Mike

  3. #3
    FEP Super Member roush235's Avatar
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    Interesting info. I always wonder why certain changes to parts are made. Probably a variety of reasons: improve performance or durability, supplier finds a way to do something cheaper, et al.
    Bob in Lebanon, TN
    79 original owner six cylinder coupe
    MCA Gold Card judge for 3rd Generation cars

  4. #4
    FEP Super Member 79mustangcobra's Avatar
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    For the 78-81, there were some that had rear defrost and some did not
    1979 Mustang Cobra 5.0
    2P Red and 1C Black

    Stock never goes out of style
    MCA #70281 - 79-93 MCA Concours Judge
    Proverbs 3:5-6



    My Mustang Story
    http://vb.foureyedpride.com/showthre...71#post1688371

  5. #5
    FEP Super Member 79mustangcobra's Avatar
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    I will take a picture of mine and post it. Mine does not have rear defrost.
    1979 Mustang Cobra 5.0
    2P Red and 1C Black

    Stock never goes out of style
    MCA #70281 - 79-93 MCA Concours Judge
    Proverbs 3:5-6



    My Mustang Story
    http://vb.foureyedpride.com/showthre...71#post1688371

  6. #6

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    Quote Originally Posted by 79mustangcobra View Post
    I will take a picture of mine and post it. Mine does not have rear defrost.
    All years had the possibility of not having rear defrost. Especially the verts.

  7. #7

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    Bump for pics please.

    I'll be deleting the dealer A/C in my '83 GT soon. I sure could use some visual references of what control unit is for what application.

    TIA

  8. #8

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    They all look pretty much the same in a photograph, the only visible differences being
    the style of blower and rear defrost switch, if it has one, and whether it's got the "Hi-Lo"
    or "Mix" setting. Can't really see backlight color in a photo.

    Are you planning to put a heater where the A/C system used to be? If so, the control
    panel for those is nothing at all like what you have now. Heaters are controlled entirely
    by cables, rather than vacuum.

    The heater panels pretty much follow the same chronology, with the '78-'79 having the
    different switches, and the '83-up having red backlighting vs blue. Any of them could
    have had rear defrost, though I believe it was a less common option on heater-only cars.
    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

  9. #9

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    Thanks for the reply.

    Hmm, this is sounding more complicated than I thought it would be.

    Let me state, I've never messed heater boxes before (only to change a heater core). I was hoping that the dealer installed A/C portion was added onto a factory non A/C heater box & as such could just be uninstalled. I'm guessing form your reply this is not the case. So in addition to finding a correct HVAC control unit & now also have to find the matching heater box and cables?

    Here is my HVAC control unit,
    There is no OFF spot??

    I found this online but wasn't sure if it was a correct replacement for what I wanted to do (plus being NOS it was pricey).

  10. #10

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    On my old '78 StaWag, the dealer air was just added on, above the heater-only air box.
    The control panel was similar to yours, except mine had the "off" position, and the A/C
    had it's own controls over the top of the added-in vent to the left of the control panel,
    where yours has that blank textured area.

    The heater-only panel you show in that second photo looks like what I had, 'ceptinfur
    mine didn't have rear defrost.

    The panel you have looks to be the same style as the NOS one, other than the labeling
    differences. The "Off" (or in your case "A/C") position just closes off the outside air.
    Perhaps it would work as-is with the heater-only setup?
    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

  11. #11

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    When did Ford go from spelling everything out in English to the @#!! pictograph @#$%!!? I thought they started that non-sense in 1981. All I know is my '83 Fairmont has the pictograph for the defrost setting (I guess Ford couldn't think up a Hi-Lo pictograph for the next setting down) and the '79 had the word defrost.

    I also noticed the ones with rear defrost the early ones with the red light were called De-Ice while the ones with the light integral with the switch shaft said Defrost.

    If I have a chance, I'll dig out and take a picture of all the ones I have - I'm sure I have the following:

    '78 with A/c no rear defrost - er I mean De-Ice
    '79 with A/C no rear defrost - whatever
    '81 heater only but with rear defrost
    '84 with A/C and rear defrost
    '86 with A/C and no rear defrost

    A couple of unknown years with A/C (I don't recall which car I harvested them from)

    One odd ball possible dealer add on A/C HVAC control unit I received from KCJones.

    Dean T
    Proud owner of the one and only Friggin' Futura

  12. #12

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    Quote Originally Posted by Dean_T View Post
    I also noticed the ones with rear defrost the early ones with the red light were called De-Ice while the ones with the light integral with the switch shaft said Defrost.
    Well, not exactly. My '79 StaWag has the separate indicator, and the lettering "R. DEF"
    below the switch. The separate indicator vs having the indicator in the switch knob is
    dependent on year, as I documented at the beginning of this thread.

    I also have another of these control pods from a wrecked '78 that is the same as
    what's in the StaWag. I have not seen one that says "De-Ice", but I don't doubt they
    may have made some with that lettering.

    Another variation I've not personally seen is "DEFOG". But this was a different feature,
    that used an electric fan/heater combo on the rear parcel shelf, rather than the grid on
    the rear glass. The DEFOG switch has Off-Low-High positions as compared to the R. DEF
    (or De-Ice) which has a center detent momentary switch.
    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

  13. #13

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    Ah heell, I think my memory is suspect. My HVAC controls with the D8 number on it are exactly as you've described: R Def. And just beneath the defrost pictograph in my '83 is HEAT. HI-LO is the second setting below the pictograph.

    I can't find the other HVACs yet but I did find one that I received from KJones. It has an E5 number on the frame, it has cable control only except for a switch mounted on the frame with a lever. I'm aready forgetting the settings but from bottom to top I think it's OFF, AC VENT HEAT DEF.

    I'll have to get a pic of it when the weather cooperates.

    Oh, I do have the rear package tray electric heater/fan assembly with the wiring and knob. It looks like the knob is mounted under the dash and it does say DEFOG on the plastic chrome bezel.

    Dean T
    Proud owner of the one and only Friggin' Futura

  14. #14

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    Interesting 'bout the defog unit. I'm wondering if that under-dash knob may have been
    a dealer add?

    The control head with the two cables and no vacuum means it's heater-only, or dealer-
    added A/C. Factory air always had the vacuum controls, even back in '67.
    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

  15. #15
    FEP Senior Member 86VertMK's Avatar
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    Quote Originally Posted by JACook View Post
    Final version, mid 1985-1986
    "Heat" and "Hi-Lo" functions are replaced with "Mix" and "Floor", which apart from having
    the positions swapped, and names changed, have slightly different functions. "Heat and
    "Floor" do exactly the same thing. "Mix" sends air to the floor and defrost vents, while
    "Hi-Lo" sends air to the floor and A/C register vents. "Mix" also engages the compressor
    clutch, while "Hi-Lo" does not.
    Sorry for not letting this one die, but if the Final version functions differently than the 2nd/3rd version as you describe, will this preclude using a 2nd in place of a final? I would like to go blue/gren illumination in my 86, but maybe I cannot...or would it be asier to cut it apart and change the lenses inside over the bulbs?
    -Mike
    Engineer by Profession (Licensed PE - Missouri)
    Mechanic by Trade (ASE Master Tech, L1, X1)

    Former Parts Counter Guy by Hobby (Chain Parts Store)
    1983 GLX Vert: GONE
    1986 LX Vert: AFR 165 5.0L/T5
    2000 Cougar: GONE
    2004 Ranger Edge 4X4
    2011 Explorer Limited
    2015 Taurus SHO PP

  16. #16

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    The difference in the "Hi-Lo" vs "Mix" positions is entirely within the control panel. The
    HVAC box under the dash didn't change for this.

    Mix is defrost + floor. Hi-Lo is dash vents + floor. If you have a red-backlit panel with
    the Hi-Lo function, you can swap the faceplate with a blue-backlit one, or you can
    swap the entire panel.

    There also does not appear to be a problem with using the earlier version that controls
    the heater restrictor door, with a later system that doesn't have the door. But you
    wouldn't want to use the later control on the earlier system.

    I'm still trying to nail down when this heater restrictor door function disappeared. It
    was either '82 or '83. Anyone have an EVTM for the '82 model year?

    <edit>
    Got an '82 EVTM, and while it doesn't show the elongated blend door, it does show the
    restrictor door was gone. This coincided with the change to the orifice tube style A/C
    system.
    </edit>
    Last edited by JACook; 11-08-2013 at 06:58 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

  17. #17
    FEP Super Member gr79's Avatar
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    Dealer add on?

  18. #18
    FEP Super Member 79mustangcobra's Avatar
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    Quote Originally Posted by gr79 View Post
    Dealer add on?
    Yes, that does look dealer ad on.
    1979 Mustang Cobra 5.0
    2P Red and 1C Black

    Stock never goes out of style
    MCA #70281 - 79-93 MCA Concours Judge
    Proverbs 3:5-6



    My Mustang Story
    http://vb.foureyedpride.com/showthre...71#post1688371

  19. #19

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    Absolutely. I had that exact same system in my old '78 StaWag. The evaporator unit was installed over
    the top of the regular heater box, and required a cut-down glove box tray. One good thing, it was much
    easier to change the heater core than on a factory air car.
    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

  20. #20
    FEP Super Member IDMooseMan's Avatar
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    This is the HVAC control setup on my 1979 Ghia, if anyone needs a reference:

    Craig "IDMooseMan" Peters
    1979 Mustang Ghia Notchback, 2.3L, Holley 5200, 4-spd, 3.08:1 7.5" diff, A/C, PS, PB, AM/FM/8-Track, Sunroof, Rear Defroster
    USAF SSgt 63170 1983 - 1992; Co-Founder, Vice President, Omega Delta Sigma, ID-A 2/2015
    To those that serve and have served, "Thank You", to those that haven't, "You're Welcome"
    2.3L Horsepower Potential Thread
    Buyer/Seller Experience Link
    Build Thread
    The Four-Eyed Game - 2018 Version

  21. #21

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    Dean_T said in post #11 that he had an HVAC control panel for an 84 with A/C and defrost. I couldn't send a pm to him. If this is available for sale, I am interested. THANKS

  22. #22
    FEP Senior Member tbirdman's Avatar
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    That post is from 2010. Your best bet is to post a message in the Classifieds in the Parts Wanted section. Be very descriptive about which type of HVAC control you are looking for.
    If they take my stapler, then I'll set the building on fire...

    85 Mustang GT

  23. #23
    Venomous Moderator Hissing Cobra's Avatar
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    Here's the HVAC unit for my '79 Cobra. When I first bought the car it had 28,667 miles on it and when I used to turn on the rear window defrost, the fan lettering would light up. I thought this was wrong and moved the bulb/wiring to the Orange light underneath the switch. Now it lights up when it's on. Is this correct or wrong?Name:  IMG_2328.jpg
Views: 249
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    Pete Slaney

    1979 Mustang Cobra

    347/T-5/4.30's
    420 rwhp/380 rwt (New Motor)
    11.49 @ 121.86

    306/T-5/4.30's (Old Motor)
    307 rwhp/278 rwt
    12.38 @ 111.38

  24. #24
    FEP Member
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    when I bought my car the dash was apart.i just replaced my hvac control with a correct rear defrost one that the pevious owner had givin me with the car.i noticed when I turn my interior lights on,it lights up the wrong color.looks white or green?where can I get the correct orange bulbs for this?

  25. #25
    FEP Power Member smitty54's Avatar
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    It's not the bulb. There is an orange tinted film that goes over the the hole where the bulb goes. To get the orange color, you would need to change the faceplate.
    "Have you ever noticed that anybody driving slower than you is an idiot, and anyone driving faster than you is a maniac."
    George Carlin, Rest in peace

    Rick
    84 GT Convertible
    68 Cougar XR7
    14 Ford Explorer Limited

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