Log In | Register
Skip to main content
Topic: Question - Air Conditioner with thermostat or without - cooling differences? (Read 549 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.
Question - Air Conditioner with thermostat or without - cooling differences?
Ok, we have our Dometic Brisk Air II HE (high efficiency) air conditioner installed and have lived with it for 2 weeks now.

The good news, with Mylar on windows, we get a 30 degree drop in temperature in the RV.  Yup, 115 outside and about 82 inside.  We are still playing with it settings but we rarely have the fan set above the lowest cooling setting.
We do have our second portable air conditioner in the front passenger seat (facing into the coach area) because we do not have the cab sealed off from the coach and the cab area gets warm (high 80s, low 90s) during the day without the second air conditioner.  The cab area is the cats domain and while the front windshield has mylar the side ones which do not get hot to the touch during the day do not have mylar (so the spoiled cats can look out).   We have turned the portable air conditioner off at times at night as it seems overkill but we are still playing with things.

Bottom line the new air conditioner cools really well, better than expected and hopefully with less power usage.   I have not confirmed that yet and while I have never lived there I have a little Mississippi - the show me state - in me , e.g. show me it really does what you say it does - I want to see those numbers on the meter.

Since our RV was not pre-wired for air conditioner (and I was not going to fish wires thru the ceiling and walls), we got the ceiling component that is non ducted with ceiling controls. 

The instructions say, when you get the RV to the temperature you want, turn the fan to cooling low speed.  And it should maintain the temperature, turning the compressor on as needed.

However, when we have the RV cooled to the temperature we want late at night (mid 70s), we get large variations as we sleep.  We set it to low cooling fan and on the temperature knob we have tried the middle and the most cold settings.  We can drop 10 degrees in the middle of the night (the outside temperature can drop 5-10 degrees) and then raise up 10-15 degrees by late morning (outside temperature can raise 10-15 degrees).   Yes, I know we are in an RV in the AZ desert with big temperature changes at night and day and we are in an RV, but the air conditioner is supposed to keep the temperature consistent by turning on and off the condenser as needed (vs running at a consistent cooling rate and just always cooling the RV a set number of degrees lower than the outside temperature).   So I am checking how others experience theirs, especially in the smaller 23/24' RV and trying to figure out how to keep the temperature more consistent.

We are getting different answers on how the thermostats work - some service/sales places say they work the same and some say they work differently).  We were also told by a well respected local service place that the wall thermostats can be 5-10 degrees off.

So my question is when you set your air conditioner at a specific cooling temperature, does it seem to pretty much hold that temperature or does it fluctuate as the outside temperature fluctuates..  Giving information on how old your air conditioner is, if you have a wall or ceiling thermostat and what you set it on would help a lot.

Thanks, Jane
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #1 –
On our LD, once the inside temperature satisfies the thermostat, the compressor shuts down.  For example, if the thermostat is set at 78 degrees, then the inside temperature will remain at a plus or minus 2 degrees day and night.  Btw, we have two (2) fans (one in the front and one in the rear) that we use with the AC.  We set both fans on the floor pushing cooler air towards the ceiling.

We place sunscreens in the front and side windows of the cab plus we use a heavy quilt to close off that area.  We've placed insulation inserts in all the vents.  In addition, we try to park so that the cab is facing the west.  We place sunscreens in the house windows and close the night shades that are receiving direct sun especially if we are unable to park under shade.  And then we extend the awning to shade the passenger side of the coach.  When we had outside temperatures of 104 and no shade, we're able to achieve an inside temperature of 78 degrees when we've used all these hot-weather camping techniques.

Hope this helps.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #2 –
Quote from: Ed & Margee  - 
And then we extend the awning to shade the passenger side of the coach.  When we had outside temperatures of 104 and no shade, we're able to achieve an inside temperature of 78 degrees when we've used all these hot-weather camping techniques.

Hope this helps.

Perhaps the awning in yours is more durable than ours. We long ago became reluctant to leave it out because more than once we have had to leap up and hold on to keep it from blowing up and over. Recently parked with winds gusting to mid-teens we just weren't comfortable leaving it out.

Were you blessed with little to no breeze or have better ways to secure it? We put the feet of ours into the mounts on the side of the rig.

Jim
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #3 –
Quote from: Jim & Gayle  - 
Perhaps the awning in yours is more durable than ours.

Whenever we extend the awning, we always anchor both ends to something secure unless we're outside and under it.   Sometimes we've used a picnic table, or run the ropes to trees, and even tie it to the Subaru.  And if the wind picks up, the awning comes down.  Finally, we never leave the awning open if we're gone.   If the passenger side of the rig is facing the Sun, we try to find a way to shade it especially in really hot temps.  Makes a big difference.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #4 –
Quote from: JandS2  - 
Ok, we have our Dometic Brisk Air II HE (high efficiency) air conditioner installed and have lived with it for 2 weeks now.

The good news, with Mylar on windows, we get a 30 degree drop in temperature in the RV.  Yup, 115 outside and about 82 inside.  We are still playing with it settings but we rarely have the fan set above the lowest cooling setting.
We do have our second portable air conditioner in the front passenger seat (facing into the coach area) because we do not have the cab sealed off from the coach and the cab area gets warm (high 80s, low 90s) during the day without the second air conditioner.  The cab area is the cats domain and while the front windshield has mylar the side ones which do not get hot to the touch during the day do not have mylar (so the spoiled cats can look out).  We have turned the portable air conditioner off at times at night as it seems overkill but we are still playing with things.

Bottom line the new air conditioner cools really well, better than expected and hopefully with less power usage.  I have not confirmed that yet and while I have never lived there I have a little Mississippi - the show me state - in me , e.g. show me it really does what you say it does - I want to see those numbers on the meter.

Since our RV was not pre-wired for air conditioner (and I was not going to fish wires thru the ceiling and walls), we got the ceiling component that is non ducted with ceiling controls. 

The instructions say, when you get the RV to the temperature you want, turn the fan to cooling low speed.  And it should maintain the temperature, turning the compressor on as needed.

However, when we have the RV cooled to the temperature we want late at night (mid 70s), we get large variations as we sleep.  We set it to low cooling fan and on the temperature knob we have tried the middle and the most cold settings.  We can drop 10 degrees in the middle of the night (the outside temperature can drop 5-10 degrees) and then raise up 10-15 degrees by late morning (outside temperature can raise 10-15 degrees).  Yes, I know we are in an RV in the AZ desert with big temperature changes at night and day and we are in an RV, but the air conditioner is supposed to keep the temperature consistent by turning on and off the condenser as needed (vs running at a consistent cooling rate and just always cooling the RV a set number of degrees lower than the outside temperature).  So I am checking how others experience theirs, especially in the smaller 23/24' RV and trying to figure out how to keep the temperature more consistent.

We are getting different answers on how the thermostats work - some service/sales places say they work the same and some say they work differently).  We were also told by a well respected local service place that the wall thermostats can be 5-10 degrees off.

So my question is when you set your air conditioner at a specific cooling temperature, does it seem to pretty much hold that temperature or does it fluctuate as the outside temperature fluctuates..  Giving information on how old your air conditioner is, if you have a wall or ceiling thermostat and what you set it on would help a lot.

Thanks, Jane
Jane, I don't know much about a/c's, but I wondering if there is a swing temperature setting on your new Brisk Air. It would be a setting that causes it to cycle off and on when the temp drops or rises x amount, say 3 or 4 degrees. Or maybe there is such an animal on your thermostat.

Curious: what kind of a portable a/c are you using?

And so as not to offend the good folks of Missouri, it is the Show-Me State. 😊

Thanks for an interesting report. RV a/c's just don't seem to work as well as old fashioned window a/c's.

Chris
Formerly: 2002 30' IB
 
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #5 –
Ed and Margee,

Have you had it stay within 2 degrees when the outside temperatures fluctuate a lot? We are thinking our 30 degree (roughly) temperature difference between coldest part of the night to hottest part of the day might be causing part / all of our issues.
Jane

Sent from Yahoo Mail for iPhone
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #6 –
Chris,
First thanks for the correction on the state - yes I have lived my whole life in the western states.

I would expect we have that couple degree range but I don’t know if it is settable.  I remember there was one jumper that looked interesting (not in installation instructions but elsewhere in the manual).   I will go back and check what that jumper does.

We have this portable air conditioner - https://www.homedepot.com/p/LG-Electronics-8-000-BTU-5-500-BTU-DOE-115-Volt-Portable-AC-w-Dehumidifier-Function-and-LCD-Remote-in-White-LP0817WSR/300422892

It works well but only cools about 5’ away.  Again it is for the spoiled cats, keeping the cab nice and cool even on very hot days.  when the RV gets warm (above 84) the cats go sit  on the floor right in front of it to stay cool.  It was a must with the old air conditioner and likely it lets us have the new air conditioner on low fan almost all the time.

We turn our passenger cab seat around to face the coach (it swivels).  The round duct goes to the cab passenger window (window rolled up holds it in place) and  we Mylar the remaining part of the window opening.

Important issue - the air going out of the rear duct to the window is hot - think 100 degrees or more.  So heater from the hose at the back of the air conditioner and cold air blowing out th front.
We wrapped Mylar (loose not fastened) around that flexible duct tubing and we can’t feel any heat coming off the duct.
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #7 –
Quote from: JandS2  - 
Have you had it stay within 2 degrees when the outside temperatures fluctuate a lot?

When the outside temps are high (20 to 25 degrees hotter than inside) then the AC will run almost continuously to try to satisfy the thermostat setting of 78 degrees.  As the outside temps cool, the AC will more easily achieve a temp of 78 degrees and gradually operates less and less.  We are able to maintain a constant inside temperature of 78-80 degrees especially when camped in shade and using all our hot weather management techniques. 
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #8 –
Jane and Scott,

When it's 115 degrees outside, and you parked mostly in the sun as I recall, it's doubtful the thermostat will ever cycle the compressor off.  With the possible exception of the warmest settings on the thermostat, it will never be satisfied under these conditons.  At some point, the heat gain of the coach through walls, ceiling, windows, people living in it, and computers generating heat, will exceed the cooling capacity of the air conditioner (sometimes referred to as the 'balance point').  Once that point is reached\exceeded, the compressor runs all the time.  I would expect that might be when the temperatures outdoors get above 95 degrees and the sun is up. 

Late in the evening, or early in the morning when the air conditioner is capable of bringing the coach down to your desired temperature, adjust the thermostat so that the it maintains that temperature.  This could take a few adjustments over an hour or so to get it where you like it.  Once you've done that, it will reliably maintain the desired temperature at night or when the temperatures outdoors are cooler in winter. During the hot summer day, it's back to running all day long.  A couple of years ago, using this method, I adjusted my thermostat setting to maintain 76 degrees in my coach.  I've never touched the setting since, and it works perfectly.  Like you, I only run the fan on Low.  On a 96 degree day, my compressor would occasionally cycle off for a few minutes, but I was in full shade.  Had I been in the sun, it would not have done so.

The electromechanical thermostat in my AC unit is highly reliable.  The technology is almost 100 years old, and is the same as is used in a multitude of applications where accurate temperature control is required.  Of course these days, more electronic type controls are being used, but the old ones were\are dependable and rarely go bad even after years of service.  If yours happens to be a newer electronic model, I would expect it to be just as reliable in maintaining your desired temperature.

With regard to wall thermostats being off by 5-10 degrees, this is nonsense.  No one would find that acceptable in their home.  Almost all, whether a modern digital thermostat or the old electromechanical ones generally have\had a two degree temperature differential built in, so for example if the thermostat was set for 78 degrees in cooling, it would turn the AC unit on when the space temperature reached 80, and off when the temperature got down to 78.  There are other things that can influence the operation, causing it to 'appear' to have large swings, for example not mounted at the correct height, near a window where the sun can shine on it, too close to a lamp, or even too close to an air register, with hot or cold air blowing right at it.  But in general, highly reliable and old technology.

I hope this is helpful!

Bill
2003 -- 23' FL
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #9 –
Quote from: JandS2  - 
Chris,
First thanks for the correction on the state - yes I have lived my whole life in the western states.

I would expect we have that couple degree range but I don’t know if it is settable.  I remember there was one jumper that looked interesting (not in installation instructions but elsewhere in the manual).  I will go back and check what that jumper does.

We have this portable air conditioner - https://www.homedepot.com/p/LG-Electronics-8-000-BTU-5-500-BTU-DOE-115-Volt-Portable-AC-w-Dehumidifier-Function-and-LCD-Remote-in-White-LP0817WSR/300422892

It works well but only cools about 5’ away.  Again it is for the spoiled cats, keeping the cab nice and cool even on very hot days.  when the RV gets warm (above 84) the cats go sit  on the floor right in front of it to stay cool.  It was a must with the old air conditioner and likely it lets us have the new air conditioner on low fan almost all the time.

We turn our passenger cab seat around to face the coach (it swivels).  The round duct goes to the cab passenger window (window rolled up holds it in place) and  we Mylar the remaining part of the window opening.

Important issue - the air going out of the rear duct to the window is hot - think 100 degrees or more.  So heater from the hose at the back of the air conditioner and cold air blowing out th front.
We wrapped Mylar (loose not fastened) around that flexible duct tubing and we can’t feel any heat coming off the duct.
Thanks, Jane. I was wondering how you vented the portable a/c.

Chris
Formerly: 2002 30' IB
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #10 –
Ed and Margee and Bill.

What you describe is exactly what I expected.  Set at one temp and compressor just run more or less as needed to keepnhat temperature.  Same as house air conditioner.

We don’t have a “temperature” tonset our air conditioner to, on he ceiling control model it only has a cooler to warmer dial with no markings for temperature.

Bill we do get down nice and cool during the daytime (again at times too cold) and rarely have the fan above low.  That  is not the issue.  Keeping a constant temperature is the issue.

That is why I am wondering if a non-thermostat model setting really is:
High cool setting = run compressor all the time (not be at a set temperature).  That would explain why in tthe middle of the night, if the compressor is running continually we drop below 60 degrees.  But in the middle of the day running all the tine gets it down to high 70s.  These numbers are from our temperature sensor that sits about Kithen cabinet height and about 2-3 feet to the rear of the coach from the air conditioner. 

However, i am not sure this is happening, as our temps dropped this week to a high of 100 (it will be cooler the rest of the month per the forecast).  So we should be getting “too cold” all the time during he day if the coldest temperature  is really saying run compressor all the time.

So we may have a thermostat failure problem or a bad design of the non-thermostat unit.  That is what I am trying to figure out.    I am not real impressed with the design of the unit based on two other minor issues. 

I think we need to check when the condenser is running - we would have to stand right under the air conditioner or go outside to hear it.  Check if it is running all the time when it gets too cold inside (day or night).

The other issue is as Ed and Margee alluded to with their two fans - air circulation.  Getting the cold air evenly distributed.  On low fan, the cold air pushes out at ceiling height for about 5’ .  At 9’ away the cold air hits the top of the twin king mattress at the back end of the coach.
I would think this indicates air flow is reasonably distributing - we do not typically occupy the space high above the twin king area (sit / lie there instead) or at the front of the coach (only going to / from bathroom or outside).

But I would really like to hear from people without a separate thermostat to see if that works different than people who have thermostats.

Thanks for the valuable info everyone. 
Jane



Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #11 –
I had a small TT with an A/C with a cooler/warmer dial.    Set it to max cool one September evening in Las Vegas when daytime was 100+.   Woke at 2 am & blowing warm.  Turns out it iced up without any down time to let the fins defrost.
Had it checked when we got to Austin, and it was fine - just a matter of 'program the user' education.

joel
Joel & Terry Wiley
dog Zeke
2013  31 IB   Orwan   / 2011 CRV Tow'd LWEROVE
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #12 –
Ok, the darned compressor is so quiet we can't tell when it comes on.  Not from inside the coach standing right under the air conditioner and not from outside the coach.  But we can definitely tell the difference in air temperature being blown out when we have it on cooling vs fan only (middle of the day test).

Joel, I read about the icing up issue.  One post said that should not happen unless outside temps are less than 65 (from a user that seemed technical like they had some air conditioning knowledge but not someone I knew).  But we only blow warm (room temp not hot) air when we do not have the cooling on, so I don't think we are hitting that issue.

I think I will need a temperature sensor up by the air supply vent as well as the typical location to see what they say over a day or two.  Not being able to hear the compressor (and yes we are young enough we should be able to hear it over the fan) makes things more difficult.  Maybe test it out when we are up on the roof right next to the air conditioner this weekend to finish our lake prevention tubing and paint the shroud (those didn't get done at install time).  Pictures of lake prevention setup will be forthcoming.
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #13 –
"Not being able to hear the compressor..."

When the compressor drops out you should be able to 'feel' a very slight shudder with your hand on the A/C unit.   ;)

As to a 'heat sensor' try a hand held infrared device, they are inexpensive and accurate. Good for tire monitoring also.   ;)
Steve S.
Lazy Bones & Cedar
2004 30'IB (Island Bed)
Yesterday is History, Tomorrow is a Mystery
Live for the day!
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #14 –
Quote from: JandS2  - 
Joel, I read about the icing up issue.  One post said that should not happen unless outside temps are less than 65
Those of us who remember non-frostfree refrigerators know how ice can build up.  Same thing happened with the radiator fins.  It was surprising that there was that much humidity in Las Vegas that night.
joel
Joel & Terry Wiley
dog Zeke
2013  31 IB   Orwan   / 2011 CRV Tow'd LWEROVE
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #15 –
Steve,
Our low fan is equivalent to the high fan setting on the old air conditioner.
It rattles the ceiling Portion quite well, and no additional vibration is felt when the compressor kicks in.
No sound changes either - I am used to that whomp sound in House  air conditioners.  Maybe we can hear or feel something on the roof side.

I was not sure of your comment about heat sensor.  Maybe I was unclear when I said temperature sensor?
I was talking about a new fangled thermometer set we use to monitor coach, fridge, and freezer temperatures (blue tooth and WiFi and storing history).
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #16 –
We might have solved some of the problem.  There are 4 side vents on the ceiling unit - front, back, and each side of the coach, as well as a bottom vent.  All can be opened or closed independently of the others.

We have the ones towards the front and back of the coach opened full.  And we had the bottom one opened full.  The side ones we had closed (1-2 feet then hit wardrobe and kitchen upper cabinets). 

I closed the vent going straight down (it is right next to the intake supply vent).  So far (only been not quite one day), the air feels more constant.
I was thinking having a vent right next to the intake might affect the temperature of the air going into the supply vent.  This seems to be the case. 
We will try it for a few days, adjusting cooling fan speed but leaving the air temp setting the same (about the 1/2 or 2/3 mark, way to cold even middle of the day when it is turned all the way to coldest) and see how it goes.
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #17 –
"But I would really like to hear from people without a separate thermostat to see if that works different than people who have thermostats.",

Jane,

If you mean with the thermostat built into the air conditioner, that is what I have, and was referring to in my previous post.

My manual says the thermostat has a range of 65 degrees to 90 degrees.  My dial can be set from 'Warm to Cool", with the numbers 2-6 in between.  With my dial set about half way between 4 and 5, my coach will stay at 76 degrees, turning the air conditioning compressor On and Off as necessary when outdoor temperatures are moderate.  As I said in my previous post, with this setting, the thermostat would turn my compressor Off for brief periods when the outdoor temperature was 96 degrees, but the compressor ran most of the time to keep up until the outdoor temperature began to come down. I know this because I was in the coach working the entire day at my computer, and I always notice when the compressor turns On and Off. I was in full shade, so I'm sure if I had been in the sun, the compressor would have run all of the time. 

Keep in mind the thermostat will not turn the compressor Off until the indoor temperature reaches the setting on the thermostat.  You said you measured 82 degrees inside when it was 115 outside. It's fairly safe to say that at that outdoor temperature, the compressor\system simply is doing all it can, so can not lower the coach temperature any further. If you have the thermostat set for 76 as I do in my coach for example, it would never turn the compressor Off in the heat of the day. As the sun goes down and\or outdoor temperatures begin to fall, at some point, you should notice the coach beginning to cool down. When the indoor temperature finally reaches 76 degrees in the coach, the thermostat will again begin turning the compressor On and Off as needed to maintain that temperature. 

From the conditions you described in your original post, it sounds to me like the AC is doing all it can during the day.  There could be something wrong with your thermostat, but I don't think so.  I would respectfully and gently urge you to follow the suggestions in my previous post for setting your thermostat, maybe starting with a setting similar to mine, or the middle of the range as a starting point if you have different settings on your dial, and adjusting over an hour or so until it maintains your desired coach temperature as measured with a good thermometer.  Then observe for a couple of days.  I think you'll find that the system will maintain the temperature you want late evenings, overnight, and early mornings, but will struggle during the day.  In cooler seasons or climates, the thermostat will control the On\Off of the compressor to maintain its setting day and night.

Finally, just a technical note:  These thermostats are temperature actuated ON\OFF switches, nothing more.  Turning them to the lowest setting will not help get the coach any cooler if the AC system can't keep up.  What is certain is if one is turned to the coolest setting, when conditions change and the system can keep up, the temperature will continue to drop until it gets too cold in the coach, and would almost certainly cause the coil to ice up as Joel described, particularly in more humid areas.  Establishing the preferred setting on the thermostat and then not touching it again is the best approach.  Another benefit of doing this is IF you're parked in a place with conditions where you know from experience that the system should be able to keep up but isn't, then there could well be a system problem that may require a service technician.

BTW, I have a 23'FL, so is same size coach as yours.
Bill
2003 -- 23' FL
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #18 –
Coming from the refrigeration field, here are my thoughts. The bottom vent is most likely your return air and it has to be unobstructed at all times. Check your filter make sure it is clean. By running your fan on low speed when you need the most cooling you are actually losing cooling capacity. The A/C has 3 speeds or so and when you go to low speed the evaporator coil isn't at full load and the condenser fan slows accordingly. As you increase fan speed you also increase the outside fan speed and the unit capacity increases and so forth until you are on max cooling. Ours is a nonducted unit also as I suspect most are.

If I were in your shoes, I would run the fan on high with the Tstat set on what ever it takes to cool the interior space to your liking. Night time can be your enemy because of the ambient temperature drop and if the A/C is set too cold it will definitely ice up and no cooling from that point on until the unit cycles off long enough to defrost.

Your discharge air vents need to be open, especially if the fan is on higher speeds. Direct them away from the return air. One thing to remember is these A/C units are marginal at best so turn them on way before the coach interior gets too warm.

Tear one of these units apart and you are going to wonder what makes them work at all.

Good luck, Jon......
1994 MB
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #19 –
Quote from: JonS  - 
Coming from the refrigeration field, here are my thoughts. The bottom vent is most likely your return air and it has to be unobstructed at all times. Check your filter make sure it is clean. By running your fan on low speed when you need the most cooling you are actually losing cooling capacity. The A/C has 3 speeds or so and when you go to low speed the evaporator coil isn't at full load and the condenser fan slows accordingly. As you increase fan speed you also increase the outside fan speed and the unit capacity increases and so forth until you are on max cooling. Ours is a nonducted unit also as I suspect most are.

If I were in your shoes, I would run the fan on high with the Tstat set on what ever it takes to cool the interior space to your liking. Night time can be your enemy because of the ambient temperature drop and if the A/C is set too cold it will definitely ice up and no cooling from that point on until the unit cycles off long enough to defrost.

Your discharge air vents need to be open, especially if the fan is on higher speeds. Direct them away from the return air. One thing to remember is these A/C units are marginal at best so turn them on way before the coach interior gets too warm.

Tear one of these units apart and you are going to wonder what makes them work at all.

Good luck, Jon......
"One thing to remember is these A/C units are marginal at best..."

Let the truth be told.

Chris
Formerly: 2002 30' IB
Re: Question - Air Conditioner with thermostat or without - cooling differences
Reply #20 –
Jon, we have on the bottom of the air conditioner (inside part) a vent (air being blown out into the coach) and a return supply (air being sucked in).  As well as the vents on the sides going in all  four directions. 

After several days use, once we closed the downward vent with only the two vents open - the one facing the back (tk area) and the front (cab area), and leaving the thermostat the same (about 3/5 way towards coldest - a sliding picture no marks), on low fan we held the same temperature 72 degrees  +- 2 degrees for 4 days even while simmering something on the stove for 45 minutes (eg. big heat output added to coach).

So I think having a vent fully open pouring out cold air right next to the air supply was making a tight circle of cold air and not letting the thermostat (inside the air supply area) get an accurate reading of the general coach temperature. 

The  crazy fluctuations are gone.
I did notice that downward vent (right next to the air supply intake) still has some cold air coming out though it is “fully closed”.  We might block that off better.

Jon, yes we have the air supply filter on a clean weekly schedule.  Nice thing we can easily see when it is starting to get dirty as tiny dust balls start forming on the “cover”, so first sign of a dustball on the cover and time to clean the filter.

You said “By running your fan on low speed when you need the most cooling you are actually losing cooling capacity. The A/C has 3 speeds or so and when you go to low speed the evaporator coil isn't at full load and the condenser fan slows accordingly. As you increase fan speed you also increase the outside fan speed and the unit capacity increases and so forth until you are on max cooling. Ours is a nonducted unit also as I suspect most are.”

That makes sense - and goes with what the manual said (loosely), high speed to cool, low speed to just maintain (eg if gets hotter inside for any reason, fan needs to be turned higher).

So far we have rarely turned the fan above low, but we are having very hot days again sometime this next week so I will do some testing regarding turning fan higher for a couple hours during he hottest part of the day.

I am not impressed at all with the design of this air conditioner.

Aside from the issue with a vent blowing cold air out less than an inch away from the air supply intake, we found: 

The cover for the air supply filter needs to be taken off to clean the filter.  There is no tabs or anything to pull it down - the local service person said he uses a pocket knife.   Bad design IMO for something that is designed to be taken off every 2 weeks (timing Dometic gave  to clean the filter).

The air vent flaps (used for some air direction) which go from shut (yup some air does leak out when they are shut) to open (45 degrees at top of opening) are poorly made.  It has two very tiny round “pegs” that fit into a hole on either side of the opening and has some plastic ridges for it to click into several positions (between fully open and fully closed). 

At one vent location the pin was sheared off on one side upon arrival.  Putting the replacement part in and making sure it was correctly in place, the pin on the same side was sheared off the first time the flap was very carefully closed then opened.  We suspect the pin hole at that spot was not drilled big enough (not yet verified).

However the thick black styrofoam they enclosed all but the coils in (on top of roof portion) does seem to be making the condenser noise undetectable.
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #21 –
I really don't like any of these RV a/c units much. I fixed a lot of them for a local RV service shop while I was still working. Yours sounds a little differant than most of them. At any rate any time the supply air can short circuit back into the return air, you are going to have problems. Make sure the lower supply air grill is directed away from the return if it is open at all and hope for the best. Safe travels, Jon...
1994 MB
Re: Question - Air Conditioner with thermostat or without - cooling differences?
Reply #22 –
I wanted to do an update. 

I still can't "hear" the air conditioner condenser go on as with the new hard foam insulation that sound doesn't travel and the fan is loud even on low.
However, a few weeks after we got this running properly, I was laying down in the twin king bed and felt the vibrations when the condenser goes on (yup thru a thick memory foam mattress when my ear was against the mattress).  Now I know what I am looking for, I can notice it vibrating the kitchen cabinets also. 
It is not easy to hear/feel, but once heard/felt and you know what you are looking for, it is noticeable when it goes on (subtle but there).

I have not yet done more than my temporary fix (blue tape across the downward outflow vents right next to the return vent), but this has held well and I only had to redo it once.  Everything runs well and as expected.  One day I will take it the lower portion apart and do a more permanent solution.
Jane & Scott
Currently have a 1989 TK  LD we did a lot of upgrades on.
Bigfoot 25RQ Twin on order with early summer 2024 ETA

Our smartphone autocorrects into very poor English.
 We disclaim the illusion of ignorance this creates as we have enough ignorance we rightly claim.