Problem with AC temp probe on 2008 330

SpyderwebSpyderweb Syracuse, NYPosts: 252Member ✭✭

Having trouble with my Marine Aire with Passport control system.  Thermostat does not seem to keep up with the actual temperature.  I’ve noticed since last year (my 1st with boat) that the temp shown on the control was usually several degrees lower than temp on a new CO monitor I bought.  I calibrated the Passport to the monitor according to manual this past weekend.  But problem still persists.

It was rainy Saturday morning so I did a test.  Temp in cabin was 79 according to Passport (and CO monitor) and I then set it to 75.  Air came on and cabin quickly cooled.  After awhile Passport read 78, CO monitor (6’ away and at same height) read 74 and a third thermometer (that was usually within a degree or 2 of CO monitor) that I located on step directly in front of the return air duct was 68.  The CO monitor and 3rd one read about how it felt.

What lead to this test was that the night before was a particularly warm night (for northern NY) and we had 6 people stay overnight.  The air would run a long time and make it quite cool (almost too much) before shutting off) and then stay off till it was way too hot before kicking back on.  The whole night went like that.  That's about how my above experiment ran.

From reading posts on this site, it sounds like either temp probe is in bad location or is shot and needs to be replaced.

Looking at back of Passport there is a flat wire with telephone type plug in back of it.  That’s how temp probe has been described. If I unplug it, passport goes blank, as if unplugged.  I expected wire to lead to temp probe located just behind inlet grill at base of v berth.  It was not there.  I eventually found this wire connected directly to the AC unit under forward compartment of v-berth.  It entered into the top of a metal boxed in area on left side of unit (above the "R" in Danger in the photo).  But coming out of the box just to the right of it was another wire, about half the width of this cable and that lead to the probe, attached to bottom of intake to AC unit itself (2nd photo)

I wanted to relocate probe to behind intake grill (near where I had 3rd thermometer placed), thinking it would give a more accurate, real time reading.  Probe cable was too short, so only got a 3rd of the way there.  Ran the AC but it made no difference.  

Seems to me I may need new probe.  If so, here’s my problem.  I don’t see any way to get into this metal box to attach new probe.  Box appears to be riveted together, not screwed. (see 3rd photo)

I’d appreciate any thoughts or ideas.  From reading older posts on here this sounded like an easy fix.  What am I missing?



  • Handymans342Handymans342 Posts: 7,599Member ✭✭✭✭✭
    You could run the fan on manual mode and see how the temp reacts with constant air flow. There should be a calibration procedure for the thermostat as well. Need book for that. 
  • SpyderwebSpyderweb Syracuse, NYPosts: 252Member ✭✭
    @Handymans342 Yes, I did calibrate thermostat to CO Monitor.  The problem seems to be the Passport thermostat seems to be very slow reacting to real time changes in temperature.  There was 68 degree air (at intake grill in cabin) being sucked towards AC unit (6 feet away under forward berth) and Passport still showed 78 degrees.  From experience the previous night, I'm pretty sure it would eventually go down to 75 (the set temperature) and shut off, but by then the actual temp in cabin might be 65.
  • Handymans342Handymans342 Posts: 7,599Member ✭✭✭✭✭
    Do the fan thing I mentioned
  • SpyderwebSpyderweb Syracuse, NYPosts: 252Member ✭✭
    I could try that next time up.
  • Handymans342Handymans342 Posts: 7,599Member ✭✭✭✭✭
    Still sounds like a thermostat issue. I had an issue similar in another boat and when I took the thermostat off the wall there was a 1 inch hole for the wire and warm air was trickling in artificially warming the stat
  • LaReaLaRea Alexandria VirginiaPosts: 3,561Member ✭✭✭✭✭
    Replace the probe.  It's about $45, but I never found one online.  Had to buy from a local shop. 

    As a short-term solution, just unplug the temp probe.  It will default to using the sensor built into the keypad.
  • SpyderwebSpyderweb Syracuse, NYPosts: 252Member ✭✭
    @LaRea and that’s my problem.  I can’t get into the metal boxed in area that the probe is plugged into.  How do I open up that riveted box shown in the last photo?
  • LaReaLaRea Alexandria VirginiaPosts: 3,561Member ✭✭✭✭✭
    The plastic knob near the "DANGER" label is some odd sort of captive screw.  It will unscrew, but mine was kind of messed up.  I got it loose, but couldn't get it re-attached.  Keep trying.  It will unscrew.  Then the box just lifts straight up.
  • LaReaLaRea Alexandria VirginiaPosts: 3,561Member ✭✭✭✭✭
    Your system has all the same symptoms that mine had.  Gotta be the sensor.
  • SpyderwebSpyderweb Syracuse, NYPosts: 252Member ✭✭
    Ah, I did play with that but it seemed to do nothing.  I'll have to work at it some more.
  • SpyderwebSpyderweb Syracuse, NYPosts: 252Member ✭✭
    Did get the screw off this weekend.  Turns out that black knob is over a Phillips screw and it slips badly.  Much easier to just use a small Phillips screwdriver, especially trying to put it back on.  Will now try and find a new sensor.  Thanks for your help.
  • Michael TMichael T Posts: 6,681Member ✭✭✭✭✭
    edited July 28
    Also - where is that "bullet-shaped" sensor located? On some boats they are located in areas that either cause artifically increased or decreased temperatures. You should have enough wire to re-locate it to an area that better represents cabin temperature. My frined's was located close to the cooled air duct. I moved it to the return air grille - result - vary close to actual cabin temperature.

  • SpyderwebSpyderweb Syracuse, NYPosts: 252Member ✭✭
    @Michael T sensor is located right on AC unit itself (see my 2nd picture above).  AC unit is under forward section of V berth.  After I got electrical box apart with @LaRea help, I found there was enough sensor cable wrapped inside that I could relocate it to the return air intake grill, located at aft end of v berth.  Same result.  Will run way longer than set temperature, and then not come back on till way above set temperature.

    I've since unplugged sensor, so now temp is controlled by sensor in Passport unit, mounted to wall, while I await delivery of new sensor.  Used it one night this way and it acts normal.  AC shuts off when set temp is reached, and comes back on when temp goes up 2 degrees.    
  • Michael TMichael T Posts: 6,681Member ✭✭✭✭✭
    @Spyderweb, your fix is quite common. Well done. Like you, many of my friends have unplugged the "bullet" remote sensor and used the "main" thermostat as the temperature control with great results - as long as it isn't in direct sunlight or a draft that main controller seems to work far better!

  • YYZRCYYZRC Georgian BayPosts: 47Member
    Where is the AC unit located in the 330?  Is it under the bed in the V-Berth?

    Thank you!
  • aero3113aero3113 Long Island, NYPosts: 2,617Member ✭✭✭✭✭
    Yes, forward V birth compartment.
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