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AC Thermostat issue

Discussion in 'Carver Yacht' started by Thisisit, Jul 27, 2017.

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  1. Thisisit, Jul 27, 2017
    #1
    Thisisit

    Thisisit Member

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    1987 3807
    The fwd AC unit is not blowing cold air. It will blow warm. My son turned the thermostat up a little each time he felt it wasn't cold enough. Now it's all the way up to the cooler side (old style 3 knob dials). If I turn it slowly towards warmer, I can hear the click in the switch. If I keep turning it, no other clicks. That tells me that the click I heard was the heat-side circuit cycling on and it does. When I turn it towards cooler, I can hear the click when its almost all the way over to cold which is the heat side circuit cycling off and it does. The dial then limits out on the cool side without another click which would normally be the cool side cycling on. (Or well before the dial limit)
    I'm thinking either the knob itself has an issue or the thermometer bulb at the intake is faulty.
    Has anyone else experienced this?
  2. g36, Jul 27, 2017
    #2
    g36

    g36 Member

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    Cruisair? I have a vertical 3 knob complete unit I removed when replacing my ac if you decide you need parts I can sell.
  3. Pascal, Jul 27, 2017
    #3
    Pascal

    Pascal Senior Member

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    These aren't worth fixing. Convert to digital. Easy and much better !
  4. Capt J, Jul 27, 2017
    #4
    Capt J

    Capt J Senior Member

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    This, and now when you need to replace a unit. The new dometic units will use either new display from cruiseair or marineair......they're not brand specific anymore.
  5. g36, Jul 27, 2017
    #5
    g36

    g36 Member

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    He may not want to spend what it cost to upgrade on a old ac unit. A fx thermostst will be a few hundred and yes they are nice. but whatever I offered a alternative that would work if that's the issue that will be way less.
  6. Capt Ralph, Jul 28, 2017
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    If it's still warm in the cabin, you will not get the warm on-click since it's already hot in the cabin your hearing the cool on/off click.
    You still have another problem.
  7. rpontual, Jul 28, 2017
    #7
    rpontual

    rpontual Member

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    You can confirm this theory by monitoring the cooling water pump. If the click you heard was the heat coming on the cooling water pump should come on and you should see water exiting the boat. (naturally this only makes sense if this is the only A/C turned on during the experiment).
  8. Capt Ralph, Jul 28, 2017
    #8
    Capt Ralph

    Capt Ralph Senior Member

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    Good idea if the compressor and the pump are wired together. Some older 3 knob controls turn the pump on when the fan is on (old start position).
    An other crude thought, put an ice cube on the bulb. Your clicks will change and you may feel two clicks for a while before it gets to cold.
  9. chesapeake46, Jul 29, 2017
    #9
    chesapeake46

    chesapeake46 Senior Member

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    Water pump comes on immediately on mine. Not wired in conjunction with the two compressors that it serves.
  10. Capt J, Jul 29, 2017
    #10
    Capt J

    Capt J Senior Member

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    It should not, it should have a trigger box so that it only comes on when 1 of the air conditioners are calling for a/c or heat. If it's on 24/7, then you have a bad trigger or bad trigger board).
  11. chesapeake46, Jul 29, 2017
    #11
    chesapeake46

    chesapeake46 Senior Member

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    I will look at the control wiring, since you mentioned it.

    The system has worked in this way for 23 years and I never questioned it.

    Edit: no card. A small Cruisair box with a power relay inside. Either compressor gets turned on and the March pump starts.

    There is some info on the data plate but I crawled in w\o my cheaters so we may never know what it says.
    Last edited: Jul 29, 2017
  12. Capt Ralph, Jul 29, 2017
    #12
    Capt Ralph

    Capt Ralph Senior Member

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    Older pump controllers (PC2 or PRC2) relied on an old solid state relay. Offering isolation between the two A/C controls.
    The older 3 knob controls, when you turned on the fan, the pump would come on then. The real old panels were labeled Start. Then after checking for water flow and fan operation, turn the knob to the Run position where the compressor would run depending on the thermostat setting and the pump & fan would continuously run. Later panels were labeled Fan then Run. Regardless of the compressor running or not, the pump runs.
    Later 3 knob controls that we commonly see today, the pump usually cycles with the compressor.
    It's all in the purple and black/red wires on the back of the 3 knob controls.
  13. rpontual, Jul 29, 2017
    #13
    rpontual

    rpontual Member

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    We may be coming accross an opportunity for the lucky owners that have the old design. It should be entertaining to upgrade the controllers to end up with higher temperature setting precision and reduction of usage to pump and fan. :rolleyes:
  14. Thisisit, Aug 2, 2017
    #14
    Thisisit

    Thisisit Member

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    Hi guys, I've been off the grid anchored in God's country. To answer some, if not all, of the questions....old style three knobs. Pump runs all the time as long as one of the units is turned on and that means to START. Always has been this way.
    Turns out the thermostat was faulty. The distributor of Dometic up here says they will fail after decades of use and that's why he has them in stock. Picked one up and installed it yesterday. All good now. They've added an extention on the copper capillary tube. Now, you run the extention past the evap coil and into the outbound air flow.
    Thanks for the input.
  15. Capt Ralph, Aug 2, 2017
    #15
    Capt Ralph

    Capt Ralph Senior Member

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    D%^M,, That's an old one (30 years?). Glad it worked out.
  16. Thisisit, Aug 2, 2017
    #16
    Thisisit

    Thisisit Member

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    Exactly 30 years.