1977-79 AC/HEATER TEMPERATURE CLIMATE CONTROL UNIT SWITCH

Discussion in 'General Ranchero Help' started by David, Dec 12, 2019.

  1. David

    David In First Gear

    Messages:
    10
    Location:
    Omaha
    I had a great luck with a Ranchero forum member pointing me to a new OEM seat belt for my '79 not too long ago. I'm throwing my line in the water again but for a AC/heater control switch. Does anyone have a thought about where to source this? New or used is acceptable. Apparently, the heater switch part of my unit doesn't work. I live in Nebraska and don't drive my Ranchero during the winter months, but not having heat does limit the months I can enjoy driving it. Any help would be greatly appreciated.
    Thanks,
    David Ranchero switch.jpg
     
  2. 72GTVA

    72GTVA Administrator Staff Member

    Messages:
    9,781
    Location:
    Chesapeake, VA
    What are the symptoms that make you think it is the heater control unit?

    - Fan doesn't work?
    - No control of the temperature?
    - None of the ventilation settings direct air where expected?
     
  3. David

    David In First Gear

    Messages:
    10
    Location:
    Omaha
    The fan does work.
    The air conditioner works - with variable temperature control available.
    The fan works while heat is selected - just no heat.
    I had replaced the vacuum actuated valve from the hot coolant hose to the heater core to no effect.
    While in for this and other service, my mechanic advised me that the "heater" portion of the climate control assembly was bad, so I am searching for a replacement.
    Thanks~
     
  4. 72GTVA

    72GTVA Administrator Staff Member

    Messages:
    9,781
    Location:
    Chesapeake, VA
    The "heat" is controlled by a mechanically operated blend door - the mechanically operated part is a cable, it is attached to the "temperature" lever and moving it to the right simply opens the blend door. You should be able to trace the cable from the control unit to the air conditioning plenum (the cable is inside a plastic tube about a 1/4" around). Once you locate it you should be able to see the lever that moves the blend door, and you should be able to see it change as you move the lever left or right.

    It could be your cable has become disconnected at either end and you just aren't opening the blend door, or the cable is broken. Is there any resistance in moving the temperature lever or does it just move freely without much resistance?

    The other possible cause for no heat is the vacuum control for the valve isn't functioning, you can test this by connecting a vacuum line from the intake manifold tree directly the valve, and you will probably have heat assuming your heater core isn't clogged.

    Final possible item, already mentioned, is a clogged heater core.
     
  5. Hillbilly

    Hillbilly In Maximum Overdrive

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    5,848
    Location:
    Winchester, TN.
    Dan, first check would be to see if the heater hoses are both hot with the engine up to operating temp. On all of my "Water Valves" the application of vacume closes the internal flapper resulting in no hot coolant going into the heater core. I would pull the vacume hose off the water valve and observe if the spring loaded diaphragm in the valve moved to the open position. With the vacume hose removed you can use your finger to move the valve between open and closed if the valve is not stuck. I have seen aftermarket valves that operated in the reverse of intended function, rule out that problem first.
     
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  6. 72GTVA

    72GTVA Administrator Staff Member

    Messages:
    9,781
    Location:
    Chesapeake, VA
    You are correct - massive brain infarction - good catch.
     
  7. David

    David In First Gear

    Messages:
    10
    Location:
    Omaha
    I've never worked on a heater core, but I've heard of flushing with Limeway. I might give that a shot before paying to have a new core put in.

    Thank you for these great ideas!!
     
  8. David

    David In First Gear

    Messages:
    10
    Location:
    Omaha
    Thank you Hillbilly. I put on an after-market valve. I will check that for malfunction.
     
  9. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
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    Location:
    Seguin, TX
    Luckily, the heater core is accessible under the hood, right where the core tubes are. If our Ranchero's were based on the follow-on Panther platform (LTD Crown Victoria, Grand Marquis, etc.), the heater box would be underdash, and a bugger to do.
     
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  10. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

    Messages:
    10,676
    Location:
    Seguin, TX
    So if replacement becomes necessary, new cores are available, and about an hour or so with hand tools to do the swap.
     
  11. David

    David In First Gear

    Messages:
    10
    Location:
    Omaha
    Thank you, Andy. That doesn't sound too difficult. I'll get the core cleaned out.

    I really appreciate all the super advice!
     

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