AC Thermostat

grouch0jrgrouch0jr Member Posts: 232 ✭✭✭
in General Boating Discussions
The AC on my boat cools just fine, but the thermostat doesn't read the ambient temperature correctly. It's probably 80° in the cabin, but the display shows 67. This is a problem because it only lets me adjust the setpoint to a minimum of 65, so it's uncomfortable. It's a Marine Air Systems unit, like the image attached. Is there a way to recalibrate this? Anyone else have this problem? 


2006 342EC - Twin Mercruiser 350 MAG MPI Horizons
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  • grouch0jrgrouch0jr Member Posts: 232 ✭✭✭
    Ok, I feel super silly for posting this, I was able to figure it out on my own immediately after posting. I found the manual online and was able to put the control panel in "program mode", then adjust the Temperature Sensor Calibration (parameter #5). I added 10 degrees to the "measured" temp, and now it's working as expected.
    2006 342EC - Twin Mercruiser 350 MAG MPI Horizons
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  • captkevincaptkevin Member Posts: 564 ✭✭✭
    It was always great when you find a quick & easy solution. Congrats
    2004 232
    2021 Yamaha Fx svho
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  • rasburyrasbury Member Posts: 8,962 ✭✭✭✭✭
    And I was pulling out the manual...
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  • MarkBMarkB Member Posts: 4,009 ✭✭✭✭✭
    The difference in temperature measurement can easily be just because of where the thermocouple is located.  Often they put it just behind the air intake filter (and the AC unit is right behind that). If the thermocouple is close to the coils (cold part of AC), then it will artificially read low.  The thermocouples normally come with a long wire, so you can actually relocate it to a more representative area.

    Boat Name: King Kong

    "Boat + Water = Fun"

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  • rasburyrasbury Member Posts: 8,962 ✭✭✭✭✭
    That's where mine is on the filter..the 270 cabin is such a size that ac works perfectly....
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  • aero3113aero3113 Member Posts: 9,849 ✭✭✭✭✭
    Mine is on the filter on the unit as well. When I replaced the system a few years ago it came with a longer sensor wire. I haven’t used it but have been wondering if I should for more accuracy. Where do most put it if they use the longer sensor wire? 
    2008 330EC
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  • aero3113aero3113 Member Posts: 9,849 ✭✭✭✭✭
    Maybe at the intake filter? Not on the filter on the unit?
    2008 330EC
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  • grouch0jrgrouch0jr Member Posts: 232 ✭✭✭
    Mine worked perfectly for all last season and the first half of this season. I doubt sensor placement would cause this issue to suddenly present itself, but I'll definitely investigate it, maybe it came loose or something.

    Typically you'd want the sensor to be measuring the actual space. The return air stream is the next best location. My intake filter is down near the floor, down there it would always measure a few degrees lower, especially because it's right near the supply register.
    2006 342EC - Twin Mercruiser 350 MAG MPI Horizons
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  • Dream_InnDream_Inn Member, Moderator Posts: 7,946 mod
    aero3113 said:
    Maybe at the intake filter? Not on the filter on the unit?
    Yep, this is where it should be and where I have mine.

    Dream 'Inn III -- 2008 400 Express

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  • SpyderwebSpyderweb Member Posts: 959 ✭✭✭
    I believe I had moved mine near the intake filter.  Seemed much more representative after that.
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