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  1. #1

    Default 86 Mustang Heat Help!

    So I got the 86 started and running! What a relief, such a good feeling to hear it fire up with no leaks, but when I hit the switch for the heat, nothing happened. I do not remember connecting any vacuum lines for the heater, the car has no A/C, and the fan does not blow or turn on when I flip the switch to ON for the heater. I checked fuse 9 in the fuse box (30amp) and it's fine, not blown.

    I'm ready for any advice or help, I just installed a 95 motor in an 86 Mustang so surely some heater vacuum routing and wiring shouldn't be awful in comparison. Where do I start? Heat it essential here when it's -2 out today.
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  2. #2

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    Are you sure that you are getting coolant into the heater core and it is just a vacuum issue where the blend door isnt moving? Is the fan blowing, like the fan inside the car so it blows outthe vents?

  3. #3

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    PS, did you use the intake from the 95?

  4. #4

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    I hear no fan turn on to even blow heat. I'm sure the coolant is routed through the heater core, it wasn't circumvented. No, the intake is an explorer upper and uses the fox style throttle body. When I hit the switch in the car to turn it "on", the LED on the switch turns on to indicate "on". I didn't include any vacuum line for my heater core in the vacuum for my motor, so where would I look for this line that needs vacuum? Also what wires could I look for that power the fan?
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  5. #5
    FEP Senior Member kbrandt's Avatar
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    The air box should default to pushing air out the defrost vents. At least that's true with the A/C cars. I assume it's the same with non-A/C air boxes.

    You shouldn't have had to change anything to get the vacuum. It is supplied by a line that penetrates the firewall by the heater core. The line goes to the vacuum tree mounted on the firewall on the driver's side.

    This is all independent of the blower fan working. If the fuse is good, then it's probably something downstream in the circuit. It could be the selector switch, fan speed switch, or the resistor pack that's in the air box. The last one is fairly common and easy enough to check by removing it with a couple of screws.
    "I want to die in my sleep like my grandfather... Not screaming and yelling like the passengers in his car." - Will Shriner

    '86 GT Mustang "Tigger"
    '95 GT convertible (wife's car)
    '86 SVO accursed car (sold)

  6. #6

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    If this car didn't have factory A/C, the system doesn't use vacuum, just a couple Bowden cables.
    Regardless, the Fox Mustangs all use a cable for the blend door.

    The blower circuit for cars without factory A/C is also very different from those with factory A/C.
    The non-A/C fan switch has an 'off' position, and the function selector lever does not turn off the
    fan.

    On the non-factory-A/C cars, the brown/orange power feed goes directly to the blower resistor unit.
    The orange and black blower wires are connected to the resistor unit, and at the end of the chain,
    the orange/black, light blue/orange, and red/orange wires go to the fan switch, which grounds the
    blower through black wire, to the main dash harness ground that's on the dash lower frame between
    the radio and glovebox.
    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

  7. #7

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    If there is any vacuum associated with it, it's not there since I swapped the motor in and the only vacuum I am running is for brake booster, PCV, fuel pressure regulator, and I'm sure I'm forgetting something, but nothing that goes inside the cabin.

    I can hear the blend door working when I flip the selector from top to bottom. I will look for the wires mentioned, I would really love to not have to remove the core as I just had my interior apart and could have done it then, ha! The selector face also shows an A/C option, too, but I'm not running any on the car.


    Sean
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  8. #8
    FEP Super Member gr79's Avatar
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    My 79 (non-ac) does that every now and then.
    Blower motor is fine.

    I move the key cyl switch (when at 'on' or running position) ever so slightly backwards toward 'off' position.
    Blower kicks on.
    Pretty sure its a worn ign. switch.

    Possible you may need a new blower motor.
    Replaced my oem one in 2000.

  9. #9

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    Quote Originally Posted by rock4451 View Post
    I would really love to not have to remove the core as I just had my interior apart and could have done it then...
    One of the advantages to the non-factory-A/C cars is heater core replacement is pretty easy. There's
    an access cover right behind the glovebox. The glovebox is the only thing you would have to remove
    to get to it.
    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

  10. #10
    FEP Senior Member kbrandt's Avatar
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    Did the car originally come with A/C?
    "I want to die in my sleep like my grandfather... Not screaming and yelling like the passengers in his car." - Will Shriner

    '86 GT Mustang "Tigger"
    '95 GT convertible (wife's car)
    '86 SVO accursed car (sold)

  11. #11

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    According to the switch inside on the instrument panel, the car did originally come with A/C. Attached are two pictures of my resistor which looks different than ones I've seen in pics of others, other ones I've seen have another small two terminal connection right next to this one...this is trying my patience for sure.


    Sean
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  12. #12

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    Sean
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  13. #13

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    The connector is C255 and I don't have one on my resistor assembly.


    Sean
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  14. #14

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    I found the connector but it wasn't by my resistors. It was just hanging by itself

    I also found this connector up by my selector switch, connected to nothing. Wire colors are orange with red, dark blue with green, grey with green, black with white, yellow with black, orange with blue. Some are faded and hard to tell.


    Sean
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  15. #15

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    Quote Originally Posted by JACook View Post
    One of the advantages to the non-factory-A/C cars is heater core replacement is pretty easy. There's
    an access cover right behind the glovebox. The glovebox is the only thing you would have to remove
    to get to it.
    I wish I wish my car do not come with A/C .
    Always Stay Humble. -Sinister-

  16. #16

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    I've seen diagrams that say my yellow with red wire should be a brown with orange wire...I'm confused as to why it's different.


    Sean
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  17. #17

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    Hi Sean,

    When you said the car has no AC, did you mean it originally had AC but all the AC equipment is gone/nonfunctional or did you mean the car had only heater/defrost and never had the AC option installed.

    I ask because in one of your pictures I thought I saw a vacuum solenoid which operates the flapper that is in front of the blower motor. This is the one that can be seen above the passenger's feet (if you had someone sitting in the front passenger seat).
    Proud owner of the one and only Friggin' Futura

  18. #18

    Default 86 Mustang Heat Help!

    To my knowledge it was a factory a/c car (and I'm only guessing that because the selector switch has an AC option and Max AC option, I got the car as a roller), but I don't have the compressor and underhood hoses installed. I don't plan on running a/c. You are right about the flapper that opens and closes above the passengers side foot area. I didn't know what it's for, so you can enlighten me if you like


    Sean
    Last edited by rock4451; 01-08-2014 at 12:34 AM.
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  19. #19
    FEP Senior Member 4EYED85's Avatar
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    If the car came with a/c you have to hook the vac. back up going through the firewall to the left of the heater core, if you are facing the engine. Are the condenser tubes still coming through the firewall, if so, the vac. line runs through the black insulation that the tubes stick out of.
    When you made the engine change did you make sure all of the hots/fusible links were hooked back up on the battery side of the starter solenoid? I tried opening the wiring diagram and looking for you, but it would not open for me. Take a meter and see if you have 12v to the fuse with the key on. The factory ignition switches in these cars are known to fall apart and "could" be a problem. The vac. has nothing to do with the blower motor running, as stated, it will just default to the defroster. Just going to have to check your hots and fusible links and probe around with a meter to rule out the blower motor itself.

  20. #20

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    Yes the fuse isn't blown and I'm getting 12v to the brown w/ orange wire, but when I check voltage at my resistor I'm only getting about 10.6 volts, would that be a reason for it not to run? What would cause the voltage to be less down by the resistor?

    There are tubes sticking out of the firewall into the engine bay, and a small vacuum line coming through, a little bit over from there as well. The opening on that vacuum line is tiny, though, it's not a normal sized one.
    Last edited by rock4451; 01-08-2014 at 10:57 AM.
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  21. #21
    FEP Senior Member 4EYED85's Avatar
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    Quote Originally Posted by rock4451 View Post
    Yes the fuse isn't blown and I'm getting 12v to the brown w/ orange wire, but when I check voltage at my resistor I'm only getting about 10.6 volts, would that be a reason for it not to run? What would cause the voltage to be less down by the resistor?
    That would be a question for JACook. I am not sure if there is a voltage drop on the circuit or you have a bad wire with resistance in it. A very easy way to tell is put a inline fuse to the hot side of the blower motor and put 12v to it and see if it spins. It really does not matter which wire either, hot to the wrong side just turns the motor in reverse, ask me how I know.

  22. #22

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    Okay, do I need to hook a ground up, too? Or is it already ground through the metal case? You're saying that 12v to either the orange or black wire should make the motor spin?....and how do you know?
    Last edited by rock4451; 01-08-2014 at 11:01 AM.
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

  23. #23
    FEP Member Tyrel's Avatar
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    I think your blower motor resistor is the wrong one. I have an 86 mustang and I just got done dealing with mine. Not sure if yours is supposed to be the same as mine but do you have any wires hanging around or another electrical clip just hanging there that your not sure where it goes? I will see if I can find a picture of what its supposed to look like. I'm pretty sure you said your car is an 86 mustang.

  24. #24
    FEP Member Tyrel's Avatar
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    Ps. If I am correct about the blower motor resistor, the part is now discontinued so your gonna have to do some hunting around like wrecker and stuff. Either way, let me know.

  25. #25

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    The resistor I have pictured is one that sits in the black box via 2 screws. Did your car come with factory A/C? I didn't see another resistor anywhere, I don't have any other wires or connectors hanging disconnected in that area, but by the switch area I do have that one connector pictured in post 14, the second picture.
    Light Regatta Blue 1986 Mustang GT 5sp - bone stock....block and rotating assembly.

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