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  1. #1
    FEP Member pre89street's Avatar
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    Default 80 mustang heater box in fairmont?

    Hi guys! Im looking to buy a 80 fairmont that have non a/c and want to put a/c in it and I have a complete a/c 80 mustang heater box and wondering if its the same as fairmont with a/c ? I know I need to relocate the hole in firewall but will it line up with stock fairmont dash?
    89 black gt
    80 chamois inline 3.3 project
    66 nightmist blue gt 4 speed

  2. #2

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    I did this years ago and it will work out fine. The boxes are the same.
    Lots of FREE F/Z info on my site.
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  3. #3
    FEP Member pre89street's Avatar
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    Do you remember if you keep the fairmont non ac heater duct on the mustang ac box?
    89 black gt
    80 chamois inline 3.3 project
    66 nightmist blue gt 4 speed

  4. #4

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    Inside the car, you need to take out the fresh air vent under the drivers side dash and plug up that hole. The air control on the passengers side is connected to the old box. Replace the heater control panel with an A/C one. Replace both dash panels to add 2 more vent outlets.
    The Mustang box and all the duct work including the parts that go to the dash pad will be needed. The duct work from the old non-A/C box is completely different. You will need the water outlet that goes on the lower part of the box from a A/C car. It is very difficult to remove without it tearing apart.
    Last edited by RED 78'; 08-07-2020 at 11:07 PM.
    Lots of FREE F/Z info on my site.
    http://myzephyrs.com

  5. #5
    FEP Member pre89street's Avatar
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    Thanks! That great info! So my only missing parts is the 2 heater duct for a/c car (dont know why bit I completely forget to remove it at junk yard), I only take heater box(water drain still like new) and the duct for a/c exit in the middle of dash and the control so my missing part under dash is the 2 heater duct for ac and fairmont dash bezel

    Another question is can I keep the fresh air vent on driver side close and it will make the same thing like I plug it when I use a/c or its because it interfer with the a/c parts?
    89 black gt
    80 chamois inline 3.3 project
    66 nightmist blue gt 4 speed

  6. #6

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    I do believe you will have to remove the whole vent. It will be in the way of the new duct work
    Here are the pictures of both sides.



    Here is a write up I made years ago on all the parts you will need to add A/C to your car. It might get confusing because I describe the parts for both available systems.
    If you do decide to use the OEM pieces first decide which year A/C you are building. There are 2 different systems. Most mechanical parts will not interchange, so don't do like I did and end up with parts for different systems. Then I did the research at the library. Nothing on the internet in the 90's.

    In the car you will need, heater box, proper lamp color heater-a/c dash control, all vent work attached to box and vacuum lines,
    new dash cluster panel with A/C vent and above glove box trim panel with A/C vent, wire harness to fuse box, wire harness to engine compartment. Also a new glove box, non-A/C were shaped differently. Maybe just the earlier years.

    Under hood you need, compressor, compressor mount, support brace, double pulley for alternator,
    hoses from heater box to mechanicals, condenser or evaporator core, accumulator or receiver or drier, new o rings for all Freon connectors, switch mounted on radiator support, or on drier, outlet to plug it into, (mine was on car above pass headlight it is green) vacuum canister for inside fender, new vacuum distributor 3 to 4 goes on firewall, square heater hose connector with hose fitting to relocate heater hose from block. (might be 6 cyl only?)

    You will need to drill 3 holes in firewall that match up with heater box. A/C, box mounting and drain.
    You should be able to see where they go they are dimpled. Replace the heater core before installing the new box.

    When getting the heater box, be very careful with the drain piece, if you damage it, it will leak in your car. It is very hard to remove, you must remove the big round plug to get to the drain spigot.

    You need to disconnect the driver side fresh air vent and detach it from up above. Then fabricate a panel to cover the hole using the piece you removed as a template, seal it with nuts and silicone.

    The only big differences in parts are the condenser, the dryer type and placement, the evaporator, the ambient temp/cutoff switch and the A/C lines, old connect with spring loks and the new have threaded fittings. The other parts can be made to work with either type but it is best to try and get them all from the same car.

    Take notes as you get the parts, just install in reverse.
    I did mine in 2 and a half days, On Memorial day weekend. Would have been 1 and a half days but I broke off the heater hose fitting in the block and that took me a day of walking to the store and back getting the tools to fix that. I could not believe that it worked! Used R-134
    I did this over 20 years ago, so no pictures worth showing.

    Oh yeah, one last thing. You might have to switch the resistor assembly on the boxes to accommodate the wiring. I did. Different years have different plug/socket combinations. The same with the vacuum line to the panel switch. That is why you should get all the parts from the same year cars.
    Lots of FREE F/Z info on my site.
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  7. #7
    FEP Member pre89street's Avatar
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    Default

    Thanks again ! Very helpful, engine side will not be a problem cause I ll make a coyote swap and will make my own hose to fit , I Have all part from a 80 mustang ( minus 2 heater duct) so that will probably the same connector for the 80 fairmont? And for the glove box can I take an a/c mustang one to pu on the fairmont?
    89 black gt
    80 chamois inline 3.3 project
    66 nightmist blue gt 4 speed

  8. #8

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    Great info, thanks!
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

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