Post edited 7:01 pm – July 7, 2011 by Lynn

Thanks Steve for the great info forum: I am an old commercial / residential contractor. Watersouce but not Marine air.

My dock neighbor has a  90' Summerset houseboat about 11 years old wtih 2 units and digital controls. One was cutting off over the weekend. When we started checking it, we had 70/260 psig, 12F subcooling and 8 SH, unit has txv. We cleaned the water strainer and head went to 255, Delta T on evap was 24 F. Unit is in crawl space under cabin. We then cleaned evap with coil cleaner (was dirty) and patched duct. Unit has 1 14x14x12" O filter grille, 3- 6" and 3- 4" flex supply ducts around the parlor. That is way too little for a low pressure system but unit has a 1/2 hp motor at 1700 rpms, so it looks like a high static set up. The boat has wooden registers on the 3- 6s (4x12) which appear to be about 75% free area. The sensor is in the ductboard return.

I think the factory installed (except wood registers) unit is under ducted resulting in high TD air side. I think it could freeze in the right situation but still do not know why it cut off on its own before getting to setpoint.

I can set it on manual fan High and it runs like craxy to setpoint at 71F. So why would it cut off in auto. I do not see any reason for pressure switches to cut it off.

What do you think?

Thanks Lynn

Post edited 12:43 pm – July 8, 2011 by Steve Pooler

Gee Lynn…I totally missed your title  

SX24C W/ SMX11 CUTS OFF WITH LO AC ON DISPLAY

That's a two ton self contained unit with variable fan…I have only installed one of those units (it was some time ago) Still don't remember it being TXV…

Ok…"LO AC" is a low voltage protection…It means the voltage to the unit has been below 200 volts for more than 3 minutes, and it shuts the unit down because of that…

Check the incoming voltage to the unit with your meter (while running) to confirm the low voltage…If it's not that low we can calibrate the control to the actual voltage in the programming mode…(it's a one time calibration setting)

We can also lie to it & tell it it's higher than it actually is, but I'm sure you know how compressors hate low voltage so I wouldn''t recommend doing that…

Pages 14 & 15 of this PDF manual cover the programming mode of the SMXII: http://www.dometic.com/FileOrg…..ration.pdf

If you need help after reading that…I'll walk you thru it  

That TD of 24 degrees does have me wondering (we look for 15 to 18 degrees) but your pressures, superheat & subcooling all look good to me…Seems you are picking up plenty of heat…Out of curiosity…Does it look like someone sweat in that TXV ???

They do call for a total of 140 square inches of discharge area & 240 square of return…

Steve~

Lynn~

I really would like to hear the end of this story  

Steve~