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heater control valve tiny hose

posted by  robertmfranklin on  Mon Oct 24 08:28 CST 2011
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last visit: Sun Sep 28 16:46 CST 2014
[RELATED]

Thanks to help from the group and the FAQs, I was able to remove the heater hose that runs from the control valve to the block. It was a bit of a challenge but with the instructions, not too bad.

When I removed the control valve, there is a rubber tube that came off of something and I cannot determine where to reattach it. The tube has an opening the size of a pencil lead and it come off the "top" of the valve.

What is this? And, where does it go?

Thanks,

Bob Franklin








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    heater control valve tiny hose

    uid 55's pic
    posted by  john sargent on  Mon Oct 24 08:50 CST 2011
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    last visit: Wed Oct 22 09:07 CST 2014
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    That is the vacuum line from heater control which closes the heater valve when you select air conditioning. There is a tiny nipple on the actuator for the heater valve. The hose pushes onto that nipple. Need a picture?
    --
    john








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      Sort of on-topic 900 1993

      uid 18083's pic
      posted by  lucid on  Mon Oct 24 09:11 CST 2011
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      last visit: Fri Oct 24 12:31 CST 2014
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      John, if AC activation closes the heater control valve, what modulates or "tempers" the cold air output when the temperature control knob is used to adjust the air temperature?

      I ask because, not seeing anything like temp "regulator" in the MCC diagram, I've always assumed (yes, I know) that AC output temperature adjustment was achieved by blending warm air from the heater with chilled air from the evaporator.

      Right, wrong, or close?

      --
      Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.








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        Sort of on-topic 900 1993

        uid 55's pic
        posted by  john sargent on  Mon Oct 24 10:05 CST 2011
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        last visit: Wed Oct 22 09:07 CST 2014
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        Bruce, sorry about not answering on your last post about this.

        I'm not an expert on the MCCs, but here goes. The early MCC had a temperature selection lever that manually located the air damper (in the heater box) to control the amount of air crossing the heater core. The later MCC, like in your and my car, has a motor that controls the position of the air damper that controls the amount of air crossing the heater core. The position of the air damper should be programmed to match the position of it to the temperature selection knob. There is no automatic regulation. You manually select a temperature, and the air damper moves to a position programmed to match the selection. If it gets hotter or colder outside, you'll need to move the temperature selector knob, to move the position of the air damper, for more or less heat.

        Some European and Australian delivery 940s had ECC (Electronic Climate Control), just like is in the 960s, and they had the inputs (to the CC) for automatic temperature regulation.

        There is a nice article, by V-Jet, who posts here occasionally, on converting an MCC car to ECC. See http://www.volvoforums.org.uk/showthread.php?t=97912
        --
        john








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          Sort of on-topic (again) 900 1993

          uid 18083's pic
          posted by  lucid on  Tue Oct 25 07:22 CST 2011
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          last visit: Fri Oct 24 12:31 CST 2014
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          Thanks John,

          That's a great explanation of how the heater output is controlled, but my question was meant to be about AC operation, for example: how is the 37° cold AC air modulated or "tempered" to something like 50°, when the temp control knob is turned in the warm direction, as I often do?

          It would seem that the heater is in play, like you described — and it's the blending of warm (heater) air with the chilled air from the evaporator that moderates the air temp coming from the vents.

          But how could that be if "activating the AC closes the heater heater control valve", or words to that effect?

          Must quit now or I'll be late for the Densa meeting.


          --
          Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.







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