Dometic Auto Fan

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Jim McSwain

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Sep 18, 2018
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My two 2019 Brisk air 2 HP with new CC 2 and new control boards. Problem in auto fan mode will not work on med fan. As long as the thermostat picks high or low all is well but when it selects Med compressor runs but no fan. Had it looked twice and the tech says the new control boards only have high and low. Any suggestions?
 
Welcome to the Forum. Can't help you with your a/c. I rarely use the medium or high on my Dometic unit. But, I'm sure others will soon respond.
 
Gary you are correct. That is what the tech said. But in Auto fan mode the thermostat selects a speed to match the tem differential. When it does, that is the problem as only the compressor is running. I need to jump the thermostat to only 2 speeds but no one knows how to that I have been able to talk with. I am ok with 2 speeds but the thermostat is trying to use 3.
Thank you for responding
 
I can tell you how to do it but ... Alas I lack one bit of info

There will be 3 wires on the T-State for fan High/Low/Medium. one of them may be N/C.. (not connected) this needs to be jumpered to one of the others (i suggest high).

You may also find (Depending on the controller on the A/C) that it has 3 wires to the fan one of which is N/C.  jumper can be done there too.  But alas without the schematic of the system i can not tell you which wires to jumper.

Page 2: I suggest not using auto fan. put it on high and leave it there.  Far less annoying as your ears and brain will block the fan noise. this "White noise" from the fan will block outside noises too like your neighbor's radio
 
A. Auto Fan
When ?AUTO? fan is selected, the fan speed will vary depending on the difference
between the temperature set-point and the room temperature. In ?AUTO? fan, the
compressor and fan will cycle ON and OFF with the thermostat.
When the difference is:
8 ?F / ?C or more The fan operates on HIGH
5 to 7 ?F / ?C The fan operates on MED
4 ?F / ?C or less The fan operates on LOW

I agree that the ac units only support a 2 speed fan.
above is from page 12 of the CCC2 Manual
I am sure a manufacture would not produce a thermostat that would not make the functions work on there ac units. That would be insane.
That being said  I ether have the wrong Thermostat for my ac units or the wrong control box. I purchased all of the equipment at the same time from the same suppler. NOT being able to operate the units in Auto Mode and Auto fan Mode makes my decision to purchase Dometic equipment a bad decision on my part . If any of you have had the same problem and come up with a process to jump the Med fan wire to the high fan wire I would love to hear how you made the wire selection. Or did you use a diference control box or Thermostat maybe I purchased the wrong components for my Bus.
I am not sure if my color code thermostat wires would be the same on any install. The control wiring was done at the factory some 14 years ago and I have just upgraded to newer models.
 
I'm pretty sure you don't disable the speed selection in the thermostat. Instead, you connect the middle speed wire to either the low or high terminal on the a/c board or its zone controller.  That way the fan runs on the that speed when the "middle" range is selected at the thermostat.  The install instructions for the thermostat should cover how to wire to the a/c control.

I think this manual covers your thermostat. If not, search online for one that does - the CCC 2 manuals are available.
http://bryantrv.com/docs2/docs/operating/Installation_CCC2%20with%20separate%20control%20box_3312792.017.pdf
 
Dometic 15000 BTU Duo Therm Brisk 2 Air RV Air Conditioner Top Unit Black

Dometic Duo Therm Brisk 2 Air Conditioner 15000 BTU Standard profile rooftop unit
From the company that invented RV refrigerator, the Dometic Duo Therm Brisk 2 Air line is powerful enough to cool even the largest coaches. Its reliability, economical price, efficient performance and long life make it the first choice of more than a million RVers today.

Duo Therm Brisk 2 Air low amp power models draw means you can run other appliances and still have power to spare. Quiet 3-speed blowers deliver the volume of air you desire. That's the right amount of cooling with no noise intrusion.

AS you can see my unit does have a 3 speed fan motor. And I do have the correct Dometic 3312020.000 Comfort Control Center 2 Multi-Zone kit control Box I also have the correct Dometic CCC2 Thermostat

To review my problem,
Fan will not work in med fan mode I have had it checked by 2 rv/ac tech and both of the say it will not work with the new control box but everything I can read say it should. Dometic is of no help because I am not a tech. Do any of you know of a good rv/ac tech in Myrtle Beach SC. I have gone through two with no help maybe 3 times is the lucky number
There is no point of buying all this high tech equipment if you are not able to use them
Thank all of you for your help
 
All I can suggest is that you search the internet for installation/wiring instructions for the Multi-zone controller.  Become knowledgeable enough to determine for yourself if it is wired correctly or not.  Maybe Dometic would send you a copy, even though you aren't a tech.  If all else fails, buy the kit online, make a copy of the relevant install & wiring info, then return for a refund.

I found a Dometic Diagnostic/service manual that has some info on the 3-speed fan.  It shows red, yellow and black wires on terminals 4,3, & 2 for Low, Medium, & High fan speeds. See pg 37

https://manualzz.com/doc/22641516/diagnostic-service-manual-roof-top-ac-hp-systems-troubles...
I also saw a note that says an incorrect phone-type communications cable between thermostat and the various zone control modules can cause incorrect results. The wire connection order is different than for a telephone, something that is difficult to discern merely by looking at it.


Far too many RV techs have little diagnostic training or experience beyond the most common a/c installations.  That makes it difficult to know whether their pronouncements on problems/solutions are accurate or not.  Sorry - I have no knowledge of a/c shops in the Myrtle Beach area.
 
Hi,

I suspect that the three wires from the thermostat share a common source (analageous to a three position selector switch). If you measure the voltage on each wire it will verify that (set the t'stat to select each fan speed - the one that doesn't run the fan is the mid range wire). If the voltages are equal or if each is a ground signal. It should (no guarantee) be safe to simply short the mid range signal wire to the high speed wire. That would give you low and high speed.

Ernie
 
The results are in. After a long wait because of the virus. I have the answer to my problem. To recap I had replaced a two ducked  AC/HP system with a new CC2 thermostat. The install went easy as it is a plug and play system for the most part. The problem I was having was that I did not have a med fan speed. This played havoc with the auto setting. The CC2 in auto runs low to a 4 degree difference and med to a 8 degree difference and over that it is on high. The new system is so much quieter than the old system and part of that is the fan speed selection. I had a certified dometic tech look at it 3 different times and his answer was that I had a two speed heatpump. After much research I found that the factory does not hook up the med fan wire ( yellow) for a change out as they do not know if you have a thermostat that will support it. To fix the unit is fairly simple. Remove cowl and foam cover of AC/HP upper unit. You will see a yellow wire that is caped off. Run this wire down to the controller and remove the cover and attach a wire connector to the yellow wire and plug it into the board on the med fan. It will be labeled. It might have a orange wire already connected to it but that is from the heatstrip plug that is not being used in my case. If it was I would tie the two together. Reinstall all covers and enjoy three fan speeds on your new AC/HP units in auto mode. The wife will love you. 
 
Jim McSwain said:
The results are in. After a long wait because of the virus. I have the answer to my problem. To recap I had replaced a two ducked AC/HP system with a new CC2 thermostat. The install went easy as it is a plug and play system for the most part. The problem I was having was that I did not have a med fan speed. This played havoc with the auto setting. The CC2 in auto runs low to a 4 degree difference and med to a 8 degree difference and over that it is on high. The new system is so much quieter than the old system and part of that is the fan speed selection. I had a certified dometic tech look at it 3 different times and his answer was that I had a two speed heatpump. After much research I found that the factory does not hook up the med fan wire ( yellow) for a change out as they do not know if you have a thermostat that will support it. To fix the unit is fairly simple. Remove cowl and foam cover of AC/HP upper unit. You will see a yellow wire that is caped off. Run this wire down to the controller and remove the cover and attach a wire connector to the yellow wire and plug it into the board on the med fan. It will be labeled. It might have a orange wire already connected to it but that is from the heatstrip plug that is not being used in my case. If it was I would tie the two together. Reinstall all covers and enjoy three fan speeds on your new AC/HP units in auto mode. The wife will love you.
Click to expand...
Great thanks!
 
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