Rheostat Installation on A/C

[Gonz]

Rheostat Install on AC.pdfHello,

I am sharing instructions I developed for installing a rheostat on the Dometic A/C so the A/C blower motor's speed and can controlled and reduced, thereby reducing the excessive air turbulence noise.

FYI, the file size is large, I apologize for this. I tried compressing the file prior to uploading, but most of the content disappeared each time I compressed the file. I also tried compressing the photos within the file, but this too did not work.

Thanks,

GG 

 

[topgun2]

Gonz - 

I assume that you have an Elite II.  Can you tell us what year you have?

Thanks.

Bill

 

[Tideline77]

This looks like a great modification!

 

thanks for the detailed instructions 

👌🏻👌🏻👌🏻

[katanapilot]

Does the Dometic noisemaker A/C have an evaporator temperature sensor?  I'm not an HVAC expert, but I would be concerned about operating the fan at too low of a speed and freezing up the evaporator.   Sorry, I didn't take the time to read the attached file.

[jd1923]

20 hours ago, Gonz said:

I am sharing instructions I developed for installing a rheostat on the Dometic A/C so the A/C blower motor's speed and can controlled and reduced, thereby reducing the excessive air turbulence noise.

This is a great idea and when we get back to high speed internet I’m looking forward to reading the PDF and trying it! Thank you.

At Inks Lake in a sea of Olivers I noted a few things. First off, if you have $1650 to spend, get the Atmos A/C! @Ronbrink’s system is amazing. In 15 minutes at the noon hour in Texas 80+ heat and humidity it cooled the interior at a whisper! Humidity dropped 11% on the gauge and I felt cool and dry before we looked at the numbers.

We run our Dometic only when necessary and set it in Auto so the fan is on only when the compressor is on. The majority of noise is inside from the loud fan at high speed. Outside it’s not near as noisy. We had a neighbor who runs theirs fan ON always. Their outside noise was double ours, likely from running it 24x7! Theirs was not only louder but I could hear bearing noise, on top of noise!

2 hours ago, katanapilot said:

would be concerned about operating the fan at too low of a speed and freezing up the evaporator.

Maybe, but likely with the fan at 50-60% it would be fine. Most A/C systems allow for multiple fan speeds, but set on AUTO ours only runs fan on HIGH. Worth a try! What are you chancing, a poor Dometic model where w/o modification needs replacing anyway?

[Geronimo John]

 

GG

Thanks for the post and procedure.  I share the thoughts of Kantanga and JD on not taking the fan speed down too low.

One safety thought from your procedure which states:

"Regarding electrical safety, none of this work should be performed without

1) first flipping the A/C breaker located in the panel under the dining table,

2) assuring the Oliver is disconnected from shore power and

3) assuring the solar system’s inverter is turned o (if your Oliver is equipped with a solar system)."

Most OTT's have inverters.  Yes you have well killed relavant breaker and power sources to the A/C unit.  But if the inverter is left on and the wrong breaker is turned off, (As it is easy to do looking at it upside down in the dark on most of our trailers), then you could be in for an "enlightening experience".  For safety sake I suggest you also list turning OFF the Inverter.

Again, great post!

Safety John  (AKA GJ)

[Ronbrink]

3 hours ago, jd1923 said:

In 15 minutes at the noon hour in Texas 80+ heat and humidity it cooled the interior at a whisper! Humidity dropped 11% on the gauge and I felt cool and dry before we looked at the numbers.

Great testament on the Atmos. Felt bad you guys had to step into the Oliver with the a/c off, but then perfect demonstration of the efficiency of the unit to quickly cool the interior while dropping the humidity! Love me some Atmos! 

[mountainoliver]

Ronbrink, thanks for showing/demonstrating your great installation of the Atmos air conditioner! I have a question though, not so much for you as it is for the Houghton second generation folks. The major issue with the second generation Houghton is that the evaporator fan (inside fan) runs continuously and supposedly raises the inside humidity level. Yet the Atmos unit (at least in Texas) operates the same and significantly reduced the humidity in the camper with a fairly significant amount of condensate running off of the camper roof. What am I missing? What’s different?

[Gonz]

All, the instructions state my Oliver is a 2021 Elite II. The instructions also state the importance of being safe and assuring no work is performed without first 1) flipping the A/C breaker in the main panel under the dining table, 2) disconnecting from shore power and 3) turning off your inverter.

A couple questions were asked about freezing the cooling coil, this is addressed in the instructions. Regarding the risk of freezing the coil, I meant to add instructions on how to visually check the coil for signs of freezing; I periodically checked the coil for freezing during the testing that I conducted and never saw signs of freezing. I will update the instructions on how to check for freezing (while the A/C is operating) in case you choose to do this modification. The check is easy to do and very safe.

[Gonz]

All, I have updated the instructions to Rev 1. The last two pages in Rev 1 outline the process for inspecting the cooling coil for signs of freezing.

 

Rheostat Install on AC rev 1.pdf

[Ronbrink]

15 hours ago, mountainoliver said:

The major issue with the second generation Houghton is that the evaporator fan (inside fan) runs continuously and supposedly raises the inside humidity level. Yet the Atmos unit (at least in Texas) operates the same and significantly reduced the humidity in the camper with a fairly significant amount of condensate running off of the camper roof. What am I missing? What’s different?

I have read that outside air being drawn in as the issue with the Houghton, but some have argued it is not and I respect that. I do know that the Atmos has significantly more airflow than my former DPll and maybe more than the Houghton, as well. That said, this increased airflow could be drying the wet coils out faster and/or more efficiently, thereby decreasing humidity levels. I too would like to better understand and hopefully someone can provide a definitive answer to your questions. 

Edited October 28 by Ronbrink

[Gonz]

On 10/26/2024 at 4:36 PM, topgun2 said:

Gonz - 

I assume that you have an Elite II.  Can you tell us what year you have?

Thanks.

Bill

 

2021

[Geronimo John]

On 10/27/2024 at 11:14 AM, mountainoliver said:

The major issue with the second generation Houghton is that the evaporator fan (inside fan) runs continuously and supposedly raises the inside humidity level.

There is no "Supposedly".  It does as reported, tested, documented and videoed on several sites.  For non-believers here is a simple demonstration procedure of the amount of moisture that their Set 2 units generate:  

• Run the stock not modified Houghton on auto cool with the T-stat set to lowest setting.  The unit will run and as it approaches set temp, the fan speed will work its way down to low.  Run for a few minutes longer.  
• The evaporator coil will be "Loaded" with condensate and you should be seeing signs of excess condensate running over the side of your trailer.
• Now cycle off the unit.  THen turn it on to heat pump and set the temp to max temp to cause the heat pump to start.
• You will now feel and sense the huge amount of moisture being evaporated off the supply air coil and being dumped into the cabin as the warm heat pump air dries out the supply air coil.

BTW, you can do this with any heat pump air conditioner.  I estimated the amount of moisture retained in the fins of our unit to be ab0ut 25 ounces.  If the fan is not cycled with the compressor, as the vast majority of ac units are designed, you can expect to see this problem.  It can be amelerated somewhat by design by changing the coil face temperature and by special coatings on the coil fins and piping.  But the results still will be unsatisfactory for most US mainland conditions.  Hence this is one of the two problems with stock Set 2 Houghtons.

My hope is that Houghton later units will be redesigned to cycle the supply air fan with the compressor, and also come with a remote thermostat.  Those two changes would make the Houghton a class leader in quality and performance.  

GJ

[mountainoliver]

John, I never said that I was a non believer! I just asked the question hoping that the issue could be explained clearly. I’m not on either side of the issue. 

[mountainoliver]

Just curious, why would I want to run the air conditioning wide open then immediately run the heat wide open? If I did that with my home heat pump/air conditioner I think that the same thing would happen. I don’t think that I remember that the air conditioner was run then the heat pump. I can understand now why a huge amount of humidity is cycled into the trailer. Maybe that explains why the Atmos unit cooled down the trailer and reduced the humidity even though the fan was running continuously, it was allowed to run a normal air conditioning cycle. Thanks for the explanation, much appreciated.

[Geronimo John]

Said differently:

The goal of the AC is to cool and dehumidify.  For dehumidification you want to be getting humidity out of the system as fast as possible.  For the Gen 2 Houghton it is by dumping it over the side.

If the supply air fan is turned off with the compressor, most of the around 23 ounces of liquid on the coil remains on the coil.  Upon start up you very quickly are kicking condensate over the side .

If the supply air fan contineues to run, most of the condensate will be moved back into the cabin.  Sort of like two steps forward and one step back thing.

Hope this helps

GJ