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89 f350 with no heat ?

Discussion in 'Ford Trucks' started by cclandscape 28, Dec 30, 2010.

  1. cclandscape 28

    cclandscape 28 Member
    from CT
    Messages: 56

    hey guys i have a 89 f 350 mason dump that the heat let go on it. The truck only has 42 thousand orginal miles. We replaced the blower motor the fuse and the heat switch itself and still have no heat. I cant figure out if theres any inline fuses i may be missing or anything else. Any help would be great. And i do have voltage to the blower motor side.
  2. hydro_37

    hydro_37 PlowSite Veteran
    from iowa
    Messages: 3,790

    heater core is plugged
  3. cclandscape 28

    cclandscape 28 Member
    from CT
    Messages: 56

    Yea i was going to check that but the blower motor will not even kick on at all with the new motor in place
  4. swtiih

    swtiih PlowSite.com Addict
    Messages: 1,179

    if the blower is blowing and the air is cold then it is probably the heater core or the thermostat is not opening. If the blower is not blowing maybe its the resistor on the fan switch
  5. FordFisherman

    FordFisherman PlowSite.com Addict
    from 06611
    Messages: 1,613

    Check for broken vacuum lines near the passenger side of the motor. Have you done plugs recently? The lines become brittle and snap if you push on them.
  6. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    If you have no blower motor running it could be the resister unit. It has the wires connected to it. It's mounted in a square cut out in the blower housing. Check your ground to the motor too.
  7. Resistor unit, relay, baffel one of those is most likely your problem or the lines attached to your temperature control
  8. Dustball

    Dustball Senior Member
    Messages: 274

    Here's where the resistor pack is mounted on the blower housing-


    Here's the diagram for your truck-

    If you say you have voltage going to your blower motor, I would look at possibly a broken ground somewhere downstream of the blower motor. The resistor pack is bypassed when the speed switch is in the high position.
  9. truckrider814

    truckrider814 Junior Member
    from va
    Messages: 10

    10-1 it's the resistor. when the symptoms are like you describe it's normally that. The core doesn't really plug up unless you add something to the mix like a fix a leak. they like to spring leaks tho. the switch not really same with the motor. just go out an buy a new resistor and replace it, their like 15 bucks and sooner or later it'd crap out anyway. keep an eye on the core and make sure it aint leaking actually inspect the core they like to have a slow leak till one day it lets the heavens go all over your floor boards. Ask me how i know, sorry for the long post it's just i have a 91 f-150 and in the past 6 years have gone through 9 more or less heater cores and 2 resistors.

    hope it helps.
  10. Dustball

    Dustball Senior Member
    Messages: 274

    If the resistor pack fails, the blower motor will still get voltage when the switch is on high as it bypasses the resistor pack completely in that position. You can see it clear as day when you look at the diagram I posted (O/BK wire from blower switch)