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Old 26-07-2019, 13:52   #1
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What does the "dehumidify" cycle on a Dometic unit do?

[Please don't answer "dehumidify"]


The so-called manual for the Dometic Turbo 12,000 BTU AC/Heat unit on the boat says there is a "dehumidify" setting and that does appear as a mode one can select. Nothing says what it does: How often it cycle, does it reduce the humidity to a certain RH, etc. Nothing.


I wrote Dometic on their user support site a week or so ago. No answer so far.


Anyone understand the setting?
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Old 26-07-2019, 14:24   #2
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What does the "dehumidify" cycle on a Dometic unit do?

It means the unit runs for a fixed amount of time (15 minutes) every 12 hours. The fan runs on low all the time. At least that is how ours worked on a boat we had about 10 years ago.
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Old 26-07-2019, 15:46   #3
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Re: What does the "dehumidify" cycle on a Dometic unit do?

I recently saw a home AC that you could set the desired humidity instead of temperature. It was for use while you were away and wanted to prevent mildew but really didn’t care about the temperature. The setting saved a lot of electricity when the house wasn’t occupied.
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Old 27-07-2019, 04:39   #4
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Re: What does the "dehumidify" cycle on a Dometic unit do?

I have similar units and located in South Louisiana. As previously stated, the system cycles for 20 minutes every 12 hours, but my fans shut down. We have high humidity, and this setting keeps mold and that musty smell at bay. It works well in New Orleans, and I never leave my boat without setting humidity mode on. Fair winds...
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Old 27-07-2019, 06:39   #5
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Re: What does the "dehumidify" cycle on a Dometic unit do?

Not sure what this particular unit does, but typically dehumidification (without cooling) is done by first passing the air over a cooling coil to wring out the water, then reheating to whatever you have set the t-stat to.

I doubt, in a marine environment, that 20 min every 12 hours is doing much to change the humidity and keep it at a set level, unless your boat is sealed up tight.

Humidity in the air redistributes very quickly (quicker than heat). That what's that 'rolling fog' is when you open a freezer, moisture moving into the cool dry air.
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Old 27-07-2019, 06:40   #6
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Re: What does the "dehumidify" cycle on a Dometic unit do?

Most new/newer A/C systems can be controlled by either temperature or humidity level meaning simply that it can be set to go on/off at selected temp or humidity levels.

Being in Florida, this is common in most new/newer homes and most of the boats here are similarly outfitted. I don’t know if it makes much difference as 90degrees is hot regardless of humidity.
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Old 27-07-2019, 09:30   #7
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Re: What does the "dehumidify" cycle on a Dometic unit do?

From the manual....



Moisture Mode

While in the On Mode simultaneously press the Power and Down Buttons. The first cycle will start in one minute. Every four hours, the fan is started and air circulated for thirty minutes. During this time the air temperature is sampled and entered into memory. The cooling cycle is started and continues until the temperature is lowered 2F (1.1C). The compressor is allowed a maximum of one hour running time to reach the desired temperature. Four hours after the temperature is satisfied or the compressor times out, the cycle is repeated. The “HU1” mnemonic code is displayed while in the Moisture Mode.
Press the Power Button to end the Moisture Mode.
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Old 27-07-2019, 10:36   #8
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Re: What does the "dehumidify" cycle on a Dometic unit do?

Quote:
Originally Posted by S/V Illusion View Post
Most new/newer A/C systems can be controlled by either temperature or humidity level meaning simply that it can be set to go on/off at selected temp or humidity levels.

Being in Florida, this is common in most new/newer homes and most of the boats here are similarly outfitted. I don’t know if it makes much difference as 90degrees is hot regardless of humidity.
I'll take a dry 90 over a humid 90, but a breeze I'll pay for

When the air is already saturated (or close to it) it won't absorb the sweat you're creating, dry air allows your natural cooling system to work more efficiently.
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Old 27-07-2019, 12:36   #9
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Re: What does the "dehumidify" cycle on a Dometic unit do?

I have one of these and use that when I’m not in town. My AC guy told me it runs the AC until it drops the temp 2 degrees from wherever the starting point. Then turns off for a fixed amount of time, then repeats. Works well on my boat which I often leave for weeks at a time. Doesn’t clog up the filter very quickly which is good.
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Old 27-07-2019, 12:57   #10
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Re: What does the "dehumidify" cycle on a Dometic unit do?

garychurch and Mabel Page you seem to be on to something. The only "operating manual" I have is a quick-start flyer which only says there is a dehumidify mode. However, reading what you wrote and looking at the flyer now I recognize some of the controlable parameters. Now I might be able to set the unit to be useable.


The boat has two units, both of which are Dometic Turbo DTU12-1161-401A, 115 V/50 Hz. A few searches on the Internet keep turning up the installation manual, but no operating manual. The units are already installed, so the installation manual is not helpful.
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Old 27-07-2019, 19:40   #11
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Re: What does the "dehumidify" cycle on a Dometic unit do?

What type of tstat/display do you have....that will show you the control logic you need to understand how it works.
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Old 28-07-2019, 04:08   #12
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Re: What does the "dehumidify" cycle on a Dometic unit do?

Quote:
Originally Posted by Dr. D View Post
garychurch and Mabel Page you seem to be on to something. The only "operating manual" I have is a quick-start flyer which only says there is a dehumidify mode. However, reading what you wrote and looking at the flyer now I recognize some of the controlable parameters. Now I might be able to set the unit to be useable.

The boat has two units, both of which are Dometic Turbo DTU12-1161-401A, 115 V/50 Hz. A few searches on the Internet keep turning up the installation manual, but no operating manual. The units are already installed, so the installation manual is not helpful.

Maybe just ask Dometic to send you a copy? When we got a new DTU installed a couple months ago, it came with a CD full of files... including an ops manual...

-Chris
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Old 29-07-2019, 08:25   #13
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Re: What does the "dehumidify" cycle on a Dometic unit do?

ranger42c was right. I received a CD and I had previously looked through the contents. The file names did not line up with the equipment. I went back to the contents, this time opening each file (well, the ones in English) until I saw the control unit pictured on the front. That is the operations manual.



The dehumidify mode does work as mentioned above. What was useful in the manual is that the parameters of the mode are adjustable and the manual states they should be adjusted for the conditions. Next time at the boat I will set the controllers for the conditions and leave the units in dehumidify mode when I leave.


Thanks to all.
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