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Old 11-19-2020, 09:56 AM   #1
Dennydj2
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How does the AUTO function on Dometic Thermostat work

I have a 2017 Alpine AL 3651 RL fifth wheel, it has two AC units, Zone 1 is main and Zone2 is Bedroom. Zone 2 options are only for AC or Fan. The options on the Dometic thermostat for Zone 1 are COOL, AUTO, HP (Heat Pump), FURN and FAN. My question is ....... what does the AUTO function do ? I have heard it will switch from AC to HP or back if needed ....... I have heard it will switch from HP to FURN if too cold for HP..... and have heard it only works with AC and will adjust the fan speed as needed. Any help on how AUTO function works will be appreciated......Thanks for the Help
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Old 11-19-2020, 10:26 AM   #2
Diver
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in most rv's the auto is the fan speed for the A.C.
in mine the heat works of the zone 1 thermo ..
but only has 1 speed fan as its in the floor ducts
with ac mode i can set auto .. or select speed of fan ..
or just run fan with out heat or ac to circulate air
mine i have to manually select heat or ac
but can run heat on zone 1 and ac on zone 2 ac
counter productive if vents are open for ac
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Old 11-19-2020, 01:42 PM   #3
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It will not switch from ac to heat automatically. It will run furnace if the heat pump can't keep up & the ambient temp drops 3-5 degrees below tstat setting. Also if you set it to hp & the temp is 3-5 degrees below that setting the furnace will kick on til the temp inside catches up.
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Old 11-25-2020, 09:18 AM   #4
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The manual indicates, yes to will automatically switch jest to cool or cool to heat based on the temperature. See page12 of the manual.

https://www.dometic.com/assets/47/55...nual_64755.pdf
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Old 11-25-2020, 01:41 PM   #5
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Quote:
Originally Posted by Dennydj2 View Post
I have a 2017 Alpine AL 3651 RL fifth wheel, it has two AC units, Zone 1 is main and Zone2 is Bedroom. Zone 2 options are only for AC or Fan. The options on the Dometic thermostat for Zone 1 are COOL, AUTO, HP (Heat Pump), FURN and FAN. My question is ....... what does the AUTO function do ? I have heard it will switch from AC to HP or back if needed ....... I have heard it will switch from HP to FURN if too cold for HP..... and have heard it only works with AC and will adjust the fan speed as needed. Any help on how AUTO function works will be appreciated......Thanks for the Help
The auto mode may be good if your in a climate with wide temp swings. Maybe mountains or desert where itís cold at night but gets pretty hot during the day. Or if your away from the rig for long periods of time and you want to maintain a set temperature both for heat and cool.
For instance if you left it on ďcool ď and went away for a week and it got really cold while you were gone then nothing would come on because the cooling set point is satisfied but it may get very cold in the rig. And likewise for heat but the opposite temp swing.
In residential systems with ďautoĒ changeover I only program auto mode for elderly or disabled persons that have a hard time getting to the thermostat to make changes seasonally.
In commercial establishments itís used more frequently because they often have a lock on the thermostat to discourage people in the office from constantly raising and lowering the thermostat to satisfy individual needs.
One thing to consider is you give away more precise control of temperature in the rv or home because in auto mode the set pints are moved out 2 deg above your requested temp and 2 deg below before either unit will kick on or some variation of that to keep your ac and heat from competing with each other and short cycling

Also donít confuse auto changeover with the fan auto setting. That merely brings the fan on automatically when the furnace or ac comes on and shuts off when either does as well.
The auto changeover would usually be in the system menu with heat cool or auto
The fan menu would usually say fan on or auto and maybe a circulate option at a lower speed
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Old 11-25-2020, 02:12 PM   #6
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I have an older camper. Auto means the fan cycles on with the A/C. The fan has two speeds that are set with a switch. The opposite setting is FAN which has the fan run all the time and we use it when the temps are not warm enough for the A/C and open windows don't circulate air enough. Some folks leave the fan on all the time so it doesn't create additional draw on the camper's electrical supply when the A/C kicks on.
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Old 11-25-2020, 02:15 PM   #7
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I've had several RVs & to date have never had one that "auto" would change from ac to heat. They've all been strictly the fan either "hi", "low" or "auto" with "hi/lo" the fan runs constantly & "auto" it only runs if ac or heat pump kicks on.
Come to think of it, never had a residential thermostat that would automatically switch from heat to cool, always had to switch it manually to either heat or cool. Even on these the fan switch has "on" or "auto".
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Old 11-25-2020, 02:28 PM   #8
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Quote:
Originally Posted by travelin texans View Post
I've had several RVs & to date have never had one that "auto" would change from ac to heat. They've all been strictly the fan either "hi", "low" or "auto" with "hi/lo" the fan runs constantly & "auto" it only runs if ac or heat pump kicks on.
Come to think of it, never had a residential thermostat that would automatically switch from heat to cool, always had to switch it manually.
Yup thatís the way auto changeover works. And I have it on my rear hvac unit on my cougar fifth wheel. The incommand mode button for rear ac gives you heat..cool ..auto ... as choices. Not the front because the rear ac unit and the rv furnace are on same zone thermostat sensor
Also Iím an hvac contractor. Being doing this since 84. Most digital (not all) thermostats made in the last 10 years have the auto option in the configuration menu. Most installers and service techs opt not to tell the customer because of nuisance service calls generated by customers unaware of the limitations of the auto setting and how it actually works.
It is usually not a ďhard mechanical buttonĒ itís a menu choice in a configuration menu that will make it appear when itís set up of never show up at all if not configured. Mostly like I said for commercial customers who donít want to send a maintenance man to every property location the first hot day to reset all the thermostats
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Old 11-25-2020, 02:38 PM   #9
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Quote:
Originally Posted by travelin texans View Post
I've had several RVs & to date have never had one that "auto" would change from ac to heat. They've all been strictly the fan either "hi", "low" or "auto" with "hi/lo" the fan runs constantly & "auto" it only runs if ac or heat pump kicks on.
Come to think of it, never had a residential thermostat that would automatically switch from heat to cool, always had to switch it manually to either heat or cool. Even on these the fan switch has "on" or "auto".
Had a new roof A/C furnace installed about 3 years ago. Thermostat does have ďautoĒ feature that will cycle from heat to cool based on temp. I choose not to use it, but I do use the WiFi feature to make changes without getting out of my chair or from the shop.
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Old 11-25-2020, 02:42 PM   #10
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Originally Posted by bjasin1 View Post
Yup thatís the way auto changeover works. And I have it on my rear hvac unit on my cougar fifth wheel. The incommand mode button for rear ac gives you heat..cool ..auto ... as choices. Not the front because the rear ac unit and the rv furnace are on same zone thermostat sensor
Also Iím an hvac contractor. Being doing this since 84. Most digital (not all) thermostats made in the last 10 years have the auto option in the configuration menu. Most installers and service techs opt not to tell the customer because of nuisance service calls generated by customers unaware of the limitations of the auto setting and how it actually works.
It is usually not a ďhard mechanical buttonĒ itís a menu choice in a configuration menu that will make it appear when itís set up of never show up at all if not configured. Mostly like I said for commercial customers who donít want to send a maintenance man to every property location the first hot day to reset all the thermostats
Also not trying to sound like a ďknow it allĒ. Itís just the one area of life I know more then I care to..... been doing it way too long lol
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Old 11-25-2020, 04:08 PM   #11
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Let’s not forget that we are talking about an inexpensive Dometic thermostat here.........For the vast majority of us, Auto just means that the fan goes on and off as the AC unit cycles. My preference is to have the fan on low all night so the fan cycling off and on all night doesn’t keep me awake
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Old 11-25-2020, 04:19 PM   #12
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[QUOTE=NH_Bulldog;423246]Letís not forget that we are talking about an inexpensive Dometic thermostat here.........For the vast majority of us, Auto just means that the fan goes on and off as the AC unit cycles. My preference is to have the fan on low all night so the fan cycling off and on all night doesnít keep me awake[/.

I was just trying to answer the opís question if itís this dometic thermostat then itís as I described. This technology isnít expensive. Itís in most newer thermostats and definitely in ones with iN∑command system. Didnít mean to make it sound fancier then it actually is
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Old 11-25-2020, 04:21 PM   #13
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Originally Posted by NH_Bulldog View Post
Letís not forget that we are talking about an inexpensive Dometic thermostat here.........For the vast majority of us, Auto just means that the fan goes on and off as the AC unit cycles. My preference is to have the fan on low all night so the fan cycling off and on all night doesnít keep me awake
And there is an ďautoĒ choice for the fan AND an auto choice separately for the mode(cool heat auto)
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Old 11-26-2020, 03:07 PM   #14
shiggs68
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[QUOTE=bjasin1;423249]
Quote:
Originally Posted by NH_Bulldog View Post
Let’s not forget that we are talking about an inexpensive Dometic thermostat here.........For the vast majority of us, Auto just means that the fan goes on and off as the AC unit cycles. My preference is to have the fan on low all night so the fan cycling off and on all night doesn’t keep me awake[/.

I was just trying to answer the op’s question if it’s this dometic thermostat then it’s as I described. This technology isn’t expensive. It’s in most newer thermostats and definitely in ones with iN∑command system. Didn’t mean to make it sound fancier then it actually is
I posted above a link to the same manual with a comment to read the Auto page.
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Old 11-26-2020, 04:51 PM   #15
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Originally Posted by NH_Bulldog View Post
Letís not forget that we are talking about an inexpensive Dometic thermostat here.........For the vast majority of us, Auto just means that the fan goes on and off as the AC unit cycles. My preference is to have the fan on low all night so the fan cycling off and on all night doesnít keep me awake

And....I will throw this out although not specifically addressing the OPs concerns.

The MicroAir Easy Touch thermostat, which I installed, does in fact have a function that will switch between AC and the heat pump. Sounds neat but after trying it don't see that it is practical. If you could set a temp level for heat and one for AC it would be different. The way it is if you set it at say 70 for night time because that is the temp you like, it is going to keep it at 70 24hrs a day. Doesn't work for me so.....I do it the old fashioned way....change it morning and night.
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Old 11-27-2020, 05:45 PM   #16
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[QUOTE=shiggs68;423385]
Quote:
Originally Posted by bjasin1 View Post

I posted above a link to the same manual with a comment to read the Auto page.
Yes I used your link for the pictures. Iím sorry if I didnít make that clear. Thanks!
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