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  • Heater woes

    The heater on my '74 won't blow out hot, or even warm air. I've checked the flow of water and made sure it runs through the heater core and the fan is working. Even with a low temp. thermostat installed it still should blow hot air. The hoses are installed correctly according the diagrams in the service manual but should it make any difference if they're not? The '74 has no cowl vent door and I assume that the outside air is blowing through the heater all the time. Does this need to be blocked off in the winter or should I be looking else where?
    ...many thanx

  • #2
    After the engine is hot turn on the heater valve (check valve on block to ensure cable has indeed opened it), turn off the heater fan, and check the hoses close to the heater unit (on the passenger's side). They should both feel hot. If not, you may have a plugged heater core. Try a flush of the cooling system with the heater valve on. May clean it out a bit.

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    • #3
      The flap inside the heat exchange has three positions, closed, vent to floor and vent to defrosters (from memory). So if the coolant/water is hot and flowing through the box, you can feel it. I thought I had a core clogging problem, when it was the valve (corroded closed inside- everything worked fine visually) above the head.

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      • #4
        I know the valve on the engine is working and I was able to flush water through the heater with a hose. I'll check the heater hose going into the heater for heat after I drive it home tonight.
        By the way, the car is running better but still not puurrfect. I advanced the timming to TDC using a strobe and vacuuum retard connected. It's been sugested that I plug the vacuum retard ports on the carbs and screw the adjustment on the temp. compensator in all the way to lock it down, then re-time it. Since I don't have to smog it I've got nothing to loose!
        Thanx again....

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        • #5
          I feel my carbs run better with temp compensation. It is an additional adjustment of mixture for warm vs cold. But if you are going to keep them from working, don't /bend destroy the bimetallic piece. They are expensive when available. If you don't want the vacumn retard, you can plug the carb. My opinions.

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          • #6
            Any critters make a nest on your heater core? :lol: It can happen...

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            • #7
              Okay, I figgured it out. The heater works fine but I'm a slow learner I guess. I realized that the round vents in the dash and under the dash have to be closed, otherwise the fan blows fresh air from the outside. So, I assume that all the heat comes from the heater flap and or the defrost vents and that the round vents are only for outside air. It would be nifty if the hot air came from the round vents too, but that's asking for too much.
              Cheers!

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