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Old 04-18-2020, 04:35 AM   #1
NH_Bulldog
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AC Fan Speeds

Although we have 3” of fresh snow on the ground this morning, we are getting the itch to hit the road soon. Thoughts have turned to spring camper prep and maintenance. One item on the list is the AC unit; a 13.5 BTU Dometic Duo Therm Brisk II. There is no noticeable difference in fan speed between low and high regardless of the thermostat setting; it seems to run on high no matter what. It does cycle on and off on auto setting and will stay on all the time if set on low or high, but the fan speed is always the same. Any ideas?
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Old 04-18-2020, 05:36 AM   #2
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Depending on what thermostat your RV is using you can enter diagnostic mode and turn on low speed or hi speed mode of fan...

Red wire to fan is for low speed operation. Black wire to fan is for hi speed operation..

If fan is running same speed from diagnostics mode ... Low and Hi speed are the same then I’d be looking at the air conditioner control module or six wire connector to the module.
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Old 04-18-2020, 05:45 AM   #3
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Areas circled in Red are fan speed outputs to six wire connector on the control module.

I’d reseat the six point connector and try fan speed operation hi and lo... you can also measure output from control module points for proper voltage output to connector and to fan motor
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Old 04-18-2020, 05:49 AM   #4
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Quote:
Originally Posted by ChuckS View Post
Depending on what thermostat your RV is using you can enter diagnostic mode and turn on low speed or hi speed mode of fan...

Red wire to fan is for low speed operation. Black wire to fan is for hi speed operation..

If fan is running same speed from diagnostics mode ... Low and Hi speed are the same then I’d be looking at the air conditioner control module or six wire connector to the module.

Thanks Chuck, I will start diagnostics this weekend. I have the Dometic 3313192 capacitive touch single zone thermostat
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Old 04-18-2020, 08:40 AM   #5
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Keep in mind as you start diags on your system that the Dometic thermostat you have has had a history of malfunctions. I put 4 in my previous trailer. Looks like you have a 19 trailer. You might look at the actual construction date and see if it might have been in 18. Per Dometic, when I was dealing with them, they had some "bad batches" in 18. Whether your unit was made in 18 or you got a "left over" thermostat made in 18, it "might" be causing you an issue although your symptoms don't sound like any of the ones I encountered. Good luck.
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Old 04-18-2020, 09:00 AM   #6
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Our build date was 8/22/18 and we purchased 4/27/19. I will do the diagnostics and see what I can find out, and then see if it might be the t-stat if nothing else shows up. I see the newer ones are Bluetooth now so maybe it might be another good excuse to replace. Thanks guys!
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Old 05-03-2020, 03:39 AM   #7
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No luck getting the t-stat into diagnostics mode. It might be because it’s a capacitive-touch single zone heat/cool. I found an old thread on a different subject and someone mentioned that theirs was the same, so maybe it’s intended that way.
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Old 05-03-2020, 03:48 AM   #8
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actually I've never notice a change in the speed on any of my RV a/c s unit.


The general rule of thumb is to just leave the setting on auto and go with that setting.
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Old 05-03-2020, 05:55 AM   #9
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actually I've never notice a change in the speed on any of my RV a/c s unit.


The general rule of thumb is to just leave the setting on auto and go with that setting.
I was thinking the same about fan speed low and high. Plugged into my 30 amp camper in the pole barn I can hear a slight difference in fan speed when switching from high to low .
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Old 05-03-2020, 06:19 AM   #10
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With the OEM rooftop A/C and the Dometic digital thermostat, the way it's "supposed to work" is like this:

With the fan switch in LOW, the rooftop fan runs on low speed
With the fan switch in HIGH, the rooftop fan runs on high speed
With the fan switch in AUTO, the rooftop fan runs on high speed if the temperature differential (thermostat selected temperature and actual sensed temperature) is greater than 5degrees F. Once the temperature differential is below 5*F the fan shuts down, changes speed to LOW (compressor continues to run) until the thermostat temperature setting is reached. When reached, the compressor will shut down, fan will continue to run for 30-60 seconds then it will also shut down.

If the temperature (within 5*F) begins to rise after the fan speed changes to low, the fan will stop (compressor continues to run) and the fan speed will change back to high. It will continue to run on high speed until the differential temperature again falls to less than 5*F difference with the set temperature and the cycle will repeat (compressor on, fan stops, changes to low and starts again),

With the fan speed set to auto, the fan will start/stop based on A/C operation. With the fan speed on high or low, the fan will run continuously as long as 120 VAC power is applied to the circuit.

If it is cooler than the thermostat setting, the fan switch will not cause the fan to turn on until the thermostat setting is reached. So, in the winter, with the thermostat set to "furn" or "heat" and the fan set to "high or low" nothing will turn on until the first time the thermostat senses a need for heat. When that happens, the furnace fan AND the A/C fan will turn on. Once the heat setting is reached, the furnace will turn off but the A/C fan will continue to run until the fan setting on the thermostat is changed to "auto"....
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Old 05-03-2020, 07:38 AM   #11
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Opinions vary on the ac/fan settings. Coming from a retail/restaurant project management in construction and facilities management it's been the "norm" to leave the fan run constantly while in cooling mode. This was always the recommendation from all the major manufactures.

Having the fan run constantly distributes the air throughout the space for a more even distribution of tempered air, filters more air, and typically gives the thermostat or the remote sensor amore "representative measurement" of the air temp over the overall space. I know comparing a 4-10 sq. ft space isn't the same as a 300 sq. ft. space but the theories are the same, the distribution of air.

In our camper we leave the fan on for the above reasons and to help "drown out" outside noise while we are gone and leave the dog behind. On the rare occasion when watching TV I'll set it to auto so I don't turn the volume up to "stadium level" to hear it.
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Old 05-03-2020, 11:05 AM   #12
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Originally Posted by flybouy View Post
Opinions vary on the ac/fan settings. Coming from a retail/restaurant project management in construction and facilities management it's been the "norm" to leave the fan run constantly while in cooling mode. This was always the recommendation from all the major manufactures.

Having the fan run constantly distributes the air throughout the space for a more even distribution of tempered air, filters more air, and typically gives the thermostat or the remote sensor amore "representative measurement" of the air temp over the overall space. I know comparing a 4-10 sq. ft space isn't the same as a 300 sq. ft. space but the theories are the same, the distribution of air.

In our camper we leave the fan on for the above reasons and to help "drown out" outside noise while we are gone and leave the dog behind. On the rare occasion when watching TV I'll set it to auto so I don't turn the volume up to "stadium level" to hear it.
. Ok I get now after having let my lady reading the post and Five minute lecture from her. Ok your dog barks a lot when your gone and your AC is noisy.
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Old 05-03-2020, 11:09 AM   #13
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. Ok I get now after having let my lady reading the post and Five minute lecture from her. Ok your dog barks a lot when your gone and your AC is noisy.
The dog doesn't bark while we are gone because we leave the noisy fan run.
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Old 05-03-2020, 11:30 AM   #14
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So I was able to get the t-stat into diagnostics mode by taking the faceplate off and touching the terminals directly with my fingers. From there, I was able to get low speed fan and high speed fan. Although the difference in sound and speed is minimal, there was a difference between the two. I think the only way to tell is to toggle them back and forth in diagnostic mode, otherwise you will be challenged to tell the difference.
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