Post edited 9:01 pm – June 14, 2011 by Steve Pooler

Hi Jason~

You got a strange one there…But probably not hard to figure out with some more info  

First from your models, you should know you have Cruisair not Marine Air equipment, but I still need to confirm what Cruisair equipment you have for sure so I know what I''m dealing with…

The FS-24C condensing unit was made for the "Original" SMX…Not SMXII, but your system may have been retrofitted by now to the SMXII….The original SMX was discontinued many years ago but we do still see a few out there…I really liked that control more than SMXII…To me it had several advantages that I won't get into here…But it was more expensive to build, install, and troubleshoot for some, thus making it more expensive to the end user all around…

To identify which SMX you have can be fairly easy:

• Check the faceplate for the term SMX or SMXII
• Remove the control from the bulkhead & look on the back at the cable connection. 
• SMX will have a 10 or 12 conductor cable with little latch type binders for each wire.
• SMXII will have only a 4 conductor cable with a flat push on male/female connection.
• SMX will have each button's function label printed on the faceplate.
• SMX had hard plastic buttons with a positive "click" when pressed.
• SMXII will have each button's function label printed on the membrane type button itself.

Next a few notes about operation of both SMX's that you may, or may not know…I'll post them so we speak the same language…They do operate the same with one exception, and both have all the same buttons in the same locations.

• Pressing any one of the top 3 buttons will cause the display to show "Setpoint" (cabin temp you are trying to maintain)
• Pressing the "Temp" the first time will show the actual temp the control sensor is registering or seeing where the the sensor is located.
• Pressing the Temp button again (and here's the difference between controls) will cause the SMX to show Outside temp or two dashes if the outside sensor was not installed.
• Pressing the Temp button the second time with SMXII will cause the display to alternate between Setpoint & Cabin temp as it sees that temp.
• Pressing the Temp button the third time with SMXII will cause the display to revert back to inside temp and stay there.
• Pressing the Temp button a third time with SMX will cause it's display to rotate from inside to outside, then cabin temp.
• Pressing the Temp button the fourth time with SMX will cause the display to revert back to current cabin temp and stay there.
• You will know what the display is showing by the Green LED being lit over the Setpoint button (means displaying SP)or if SMX it has a couple extra LED's for inside and outside temps…

The display rotating feature is so that you don't have to get up & press a button to see where you are at…Great when the Admiral say's it's Too Hot, or Too Cold in here    It will continue to rotate until you get up & press a button such as Temp or Setpoint…With either control, Pressing Setpoint will cause the display to stay at the temp you are trying to maintain (indicated by the LED above the button being lit)

Anyway…I posted it so that we don't get confused when talking about it, also for others info, and it may save us all some posts…It can also be part of your issue…The display is rotating and you didn't know it was a feature…

Back to your issue…

I'm not sure why someone told you that the sensor needs to be sticking out in the room unless you (or them) have set the control to cycle the fan with the compressor instead of running continuously as it comes programmed from the factory. 

This could be part of your problem due to location of that sensor and if it is sticking out where cold discharge air from one of the grilles can blow on it making it think it's colder than it really is…Maybe this is why blowing a fan on it seems to help ?…The fan blows the cold air away from it ???

Is this a overhead unit ?…Meaning Discharge & Return vents in the headliner ?

It's common for those type units to get cold return right back into the return due to louver adjustment of the discharge grills…And adjusting those louvers so that air blows away from the return grill may solve the temp sensing problem…

Sometimes (depending on grill & louver design) this may entail removing the grille/s and rotating them 90 or 180 degrees to get the louvers to face another direction…Or it may entail a differing style grille…

But really…You never want the A/C to recirculate it's own cold air…It will cause the coil to ice up & block air flow among other things that can cause harm to the system, and for the purpose of this discussion, I don't really need to describe…

If you have set the control so that it cycles the fan with the compressor and would like to keep it that way…Then we should probably look for another location for the sensor which is not always easy on a boat…I'll try to explain….

• With continuous fan, and the sensor in the return path/grill…The sensor is seeing a constant "Average" temp of that whole cabin because of the constant flow of cabin air over it…
• With intermittent fan (as it's called) the sensor can only sense temp At It's location.
• Finding a suitable "permanent" location that does not get heat (or cold ) from another source such as windows, hatches, un-insulated overheads, engine room bulkheads, etc…can be tough…
• Also take into consideration that boats don't always face the same direction to the sun as a house would.

If all this seems to be ok…Then we could have a connection problem with the sensor leads where with that bad/corroded connection the resistance measured thru the sensor by the control is not constant with regard to temp changes…Sometimes it's just a matter of cleaning some connections….

Hope this was not too long & boring, and that it helps…

Get back to me with your findings, and or questions Jason…I'm sure all of us would like to know your answer…

Steve~

Post edited 4:33 pm – June 14, 2011 by Steve Pooler

Ok Jason~

From your description the SMXII is programmed for intermittent fan…

Do you have your SMXII manual ?…I'd like you to set the control back to continuous fan, put the sensor back behind the return grill (making sure it does not touch a wall or cold coil) and see if that solves the issue…

If you don't have the manual, or don't know how to program the control, I can post a link to the manual and then walk you thru it if needed…Either here, or by phone when you are on the boat and in front of the control…

Steve~

Jason~

Looks like you have a F"X"-24 in the engine room…Not a F or FS-24…That's where you had me confused…

Start reading on page 8 of the owners manual…Top of page 10 is "Fan Mode" that I spoke of….

I was thinking you would call me when you were in front of the control if you had a problem…My number is in the Contact Steve link at the top of every page here…But read the programming section first so we are talking the same language…

Steve~

SMXII Owner/Operation Manual:

http://www.dometic.com/FileOrg…..ration.pdf

Bonus    SMXII Installation Manual:

http://www.dometic.com/FileOrg…..ration.pdf

You are right Jason…

Gosh…It completely slipped my mind that they did for a brief period change the designation for a SMXII condensing unit to "F" from FX …Now days they designate them "RX"…I was thinking that maybe the S or X had worn off the label on your unit (FS being for original SMX)

This change from Marine Development Corp Cruisair (which it was for 40 or so years) to Taylor Made, and now Dometic has been a little confusing for us older MDC Cruisair guys  

Anyway…Did you get a chance to read the pages I pointed out ?

Still more than happy to walk you thru it if needed….

Steve~

Thats why I said to call me & I'll walk you thru it…It's easier that way, but it seems you are not going far enough…

There are 14 user adjustable parameters in the program mode, and each has a combo of buttons to press (depending on what parameter you want to access) after you do the OFF then SET…

In this case…

You must first press OFF followed by SET then "Simultaneously" (All at the same time) press DOWN, FAN & UP…The display should then read "I" for intermittent with a decimal point in the bottom right of the display…(If it does not show this decimal indicating you are in the program mode, then you likely didn't press them exactly at the same time)…You then change that to "C" for continuous, by pressing "Either" the UP or Down button…Then press OFF to save & exit the programming mode.

If you call me I can walk you thru other features that can better the system's operation while we are at it…

Let me know how you go 

Steve~

PS: Yes, there are three brightness levels that are accessed by simply pressing the set button…Each time it is pressed (after the first time) it will change the display brightness.