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How much below outside temperature does your air conditioner cool?


Vladimir

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I noticed in Wenatchee that our Carrier air conditioner has a hard time keeping up with outside temps.

 

It is just a hot in Arizona. Today, in Gila Bend it is 103 degrees outside....and 87 degrees inside. The lady at the RV park said her's will cool 20 degrees below outside no more!!

 

Conditions....full sun, no shade.

 

So how low do you go??

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The answer is not so simple. An air conditioner should lower the temperature of the air coming into it by about 20 degrees. Humidity plays a role, as does the size of the air conditioner. 20 degrees is about average. Keep in mind that this is all about cooling the air that is already inside the RV. It is not about how much it will cool below the outside temperature.

 

As far as how much cooler than the outside temperature can an RV air conditioner cool, well, that depends on a lot of things. How many cubic feet of air in the rig? How much insulation does the rig have in it? How reflective is the outer surface of the rig? How big are the air conditioners (BTU's) and how many of them do you have? How efficient are they? Are the inside and outside fins clean? Are the filters clean? Are you cooking in the rig? Do you have a residential refrigerator that exhausts it's heat into the rig? How many lights do you have on, and how much heat do they put out? How much heat do your computers etc. put out?

 

The point is that there is no good answer. Generally, the higher quality the RV, the better it is able to withstand high outside temperatures. Our rig isis a 43 foot Teton.5er with three slide outs. It is a very well built unit. We have spent the summer in Phoenix and had many days where the temperature is in the 115 range. Our rig is white, and we are in full sun. We have two 15,000 but Dometic heat pumps that are ducted. On days when the temperature is expected to exceed 110 I manually turn the fan on high. Even on 115 days we have been comfortable inside with temperatures never exceeding 80.

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Our mh has never been hard to heat or cool when parked. I run the front ac(stat set on 72) only until the outside temps get into the 90's then the rear ac is usually turned on and the stat is set at 73-74. (Both units are 13.5 Dometics) Another thing that I've learned is when the outside temps move into the 90's, I turn the ac fans on manual which seems to really keep the inside temps very comfortable, usually in the 72-74 degree range. Proper maintenance and filter changes/cleaning is also a must. We just got back from 2 weeks in Tx , around Conroe, Port Aransas and Livingston which was a good test for the ac's.

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Our MH is not hard to cool either. Most of it is white, including the roof. I think that makes a huge difference vs the newer dark colored rvs. We find ourselves turning the temperature up because we are getting too cool. When you chase the sun, you get used to warmer temps.

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We found that reducing the heat coming into the RV was the answer for our summer camping in the southwest. Awnings over the windows helps some, a snap-on sun screen helps more and if you pick a darker color you can still see out. For windows you don't use often adding a sheet of Reflectrix bubble-foil insulation will do even more. Reflectrix is also great in vents and skylights.

 

If you have slides but no awnings over them you can also increase the roof insulation on them, either foam blocks or more Reflectrix will work well, tie either down well in anticipation of wind gusts though.

 

We got almost 20 degrees cooler than we originally got on a hot, sunny summer day in Pahrumph, NV by adding the above.

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I agree with all of the above. If you can get 20 degrees difference between the return air and the discharge air on any A/C it is doing its job.

Heat gain is a big factor so if for example you have a white RV and dual pane windows that helps. Shading your windows helps very much. I have the lttle awnings on each of my windows and when they are deployed it makes a big difference.

 

It helps to run the A/C early enough in the day so that it is maintaining the temp in the RV rather than trying to pull the temp down from hot.

Good maintenance on the A/C helps too. Clean or replace the filters, clean the evaporator and condensor periodically, straighten fins if bent. Some people have found that their A/C leaks some of the precious cool air into their "attic" and by doing simple mods to fix this they get better results.....this mod you can find on forums or youtube.

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We try to follow the 70-80 degree weather. There was a thread on this site a couple years ago that discussed where to go to keep cool in summer. That helps, but we don't have trouble keeping our MH cool.

 

 

When we started full-timing 5 years ago we adopted the maxim of following 70 degrees. Although that's not always possible, the absolute hottest day we experienced this summer on Prince Edward Island was 82. Sure we can cool the MH, but it's even better not to need to. In the winter we don't go anywhere where the temperature goes below 32! If we have the right to choose, why not choose what's best for us?

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Plugging leaks in the AC unit is easy and cheap, not a big change but anything to quit sweating! We used duct-tape (not duck tape) thin aluminum (no cloth or plastic) tape with a strong adhesive on ours.

 

We started off with an alcohol soaked rag so the tape had a clean spot to stick, wiped the area around the hole off and stuck on a square of tape. We removed the outside and inside covers and worked on the inside, the bright sun made any holes easy to spot. Waited for evening, got out a bright light to put inside and went up on the roof and did the outside. Some holes could be seen from both sides but were easier to get to from one side or another.

 

When we got done the unit was a bit quieter in operation but we didn't notice any big change in the cooling ability. If you do this there are usually two drain holes that let water escape, do not cover them!

 

We also checked all of the duct work we could reach hoping to find a leak but as far as we could tell it was all solidly connected. We were hoping for a leak so we could get a bit cooler!

 

 

Something I forgot to mention was running the unit with the fan always on, that made a difference when it was over 110 outside as sometimes the unit would not start if we let the fan cycle. We never really figured out the reason why as we quit worrying about it and just let the fan run.

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I read the above post regarding SE Texas in the summer as a good test

of your ACs and I couldn't agree more. I have been in Livingston, TX in late July

with the temp in the high 90s F and the humidity about 90%. My two ACs, 15,000 btu

and 13,500 btu, ran all day but they did cool the air by 21 degrees F. Good Luck

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About 20 degrees is the general rule-of-thumb. Our single ducted AC can get us to about 25 below ambient, but we have optional insulation with a cold weather package.

 

Slide awnings will make a big difference. Also, as noted above, put the AC fan on manual and let it run all the time, keeps the temps more even throughout the rig.

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The answer is not so simple. An air conditioner should lower the temperature of the air coming into it by about 20 degrees. Humidity plays a role, as does the size of the air conditioner. 20 degrees is about average. Keep in mind that this is all about cooling the air that is already inside the RV. It is not about how much it will cool below the outside temperature..

 

Plugging leaks in the AC unit is easy and cheap, not a big change but anything to quit sweating! We used duct-tape (not duck tape) thin aluminum (no cloth or plastic) tape with a strong adhesive on ours.

These two give some of the best advice in the thread, although there is a lot more here. On the cooling ability of the air conditioner, whether it is in a stick house or an RV, the ability it has to cool can only be measured by temperature differential between air into and out of the cooling coils. (for an RV normal is no less than 18° and not greater than 24° for most units) The BTU capacity of the unit is one of the factors in it's ability to cool a particular space but just as important is the total volume of space being cooled, the quality and amount of insulation it has, the amount of air intrusion from outside, and many other design features of the RV in question. There is a great difference between the heat gain from a typical RV window and a dual pane window and that is a major contributor to consider if buying, but hard to retrofit if not installed when built. As Stanley suggests, you can improve the situation by using one of the insulating window covers, but you live in a cave if you do so. I have used a reflective windshield cover on the outside which you can see through and like those but they don't do as much for you.

 

To help to seal from air intrusion, I used expanding foam around plumbing and electrical openings for the most part. Like Stanley, I don't use cheap duct tape for anything of importance. Having worked for 3M Co. I may be prejudiced, but I prefer to use their brand of duct tape because it holds for a long time and seldom leaves much adhesive behind when removed. The metallic type can be better in many instances.

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We have an Alfa 40' fiver with two basement A/Cs. There is a love/hate relationship with these units among Alfa owners. We have always liked ours along with the heat pump on chilly mornings. We have been in Boulder City, NV. for a week now and most days have topped out at 103. Our thermostat is set for 75. It generally has been holding at 77 to a high of 80 (daytime) depending how much we are in and out. Here is what we have found in 12 years of use of these A/Cs. We don't care for A/C but sometimes you have to bite the bullet. We keep the fiver closed up all the time. In other words, when it is say 74 in the morning and we would ordinarily open doors and windows until the heat starts to rise. But we find it cools much better leaving the rig closed up. Another big help and probably the best is running the ceiling fan as it moves a bunch of air. We do have slide covers and window awnings which we also like and think they do help. We have a lot of window area and the rig is white. The venetian blinds are tilted, not closed, while the sun is on that particular window. Like numerous other posters have said, there are so many variables involved and how much humidity is in the air is a big factor.

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  • 3 weeks later...

Adding to the list of things that may help an air conditioner cool the RV better:

Clean the condenser and evaporator coils of any dirt, lint, etc - gently, so you don't bend the flimsy aluminum radiating fins. Straighten any bent fins with a fin comb. If you have return air filters, make sure they are clean. I replaced the OEM foam filters with Filtrette brand filter material because I have asthma. This means I must replace the filter media at least once/twice a month to avoid restricting air flow excessively, and reducing cooling efficiency.

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  • 5 months later...

We just did a re-taping repair of our duct work and our A/C is much better now. We have a new unit as of a year ago. I have a temperature gun and it was reading 40 degrees a few days ago when it was 95 degrees outside. We got the inside down to 83. Anyone know why I'm getting such a low temperature on the vent outlets? I use to be happy if it was over 20 degrees lower that outside. We are in Quartzsite, AZ in the desert. Could this really low outlet temp be because we are in such a dry climate?

 

Our repair is blogged here: http://www.walkaboutwithwheels.blogspot.com/2016/03/duct-duct-whoosh.html

 

 

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We just did a re-taping repair of our duct work and our A/C is much better now. We have a new unit as of a year ago. I have a temperature gun and it was reading 40 degrees a few days ago when it was 95 degrees outside. We got the inside down to 83. Anyone know why I'm getting such a low temperature on the vent outlets? I use to be happy if it was over 20 degrees lower that outside. We are in Quartzsite, AZ in the desert. Could this really low outlet temp be because we are in such a dry climate?

It is important to remember that the amount of cooling inside can't be compared to the outside temperatures, even though they do have some impact upon cooling because it effects the heat transfer for the heat of compression that is removed by outside air. To measure the cooling inside you need to measure first the temperature of the air entering in the the return air side of the system and then measure the temperature of the air that is blowing into the RV. What the air conditioning people call it is delta T (Δt) and it is the change in temperature of the air as it passes though the cooling coils. While I'm not very familiar with the basement RV units, I am quite familiar with roof units and even the home window units. In both cases what is looked for is a Δt of no less than 18° and no greater than 24° with a target of 20/22°.

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Trying to evaluate your A/C cooling based on out door temperature is wrong. A properly operating roof top RV A/C with the fan running on high speed will cool the room are temperature 18 to 20 degF. Use a thermometer (not an infrared) to measure the temperature at the closest air outlet to the unit then at the air intake to the unit. The leaving air should be 18 to 20 degF lower than the inlet temperature.

 

To cool an RV try to park in the shade, especially away from the afternoon sun, use heaat reflective film in the windows or solar screens.

 

In the south, any RV over about 28 to 30 feet should have two units.

 

Ken

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The term Air Conditioner is doing just that. The AC unit is not only reducing the air temperature but it is conditioning the air by removing the humidity thus you feel more comfortable. Another factor is the number of people and pets someone may have inside either their RV or personal vehicle. We all produce heat and the more heat produced the harder the AC must work. Cooking using the stove or oven will also adversely impact interior temps. Think about how much heat is given off from electronic equipment. It all adds up!

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  • 4 weeks later...

OK...I've said this before and have had people tell me" I'm full of it"! My first time out with the motor home we went to Pahrump, Nv and I had two 13.5 air's, outside temp's, a dry 113. we were wearing sweat shirts in the MH, I had it in the 60'ies. No outside shade, awning's deployed at Terrible's (Lakeside) RV Resort. Last time we went to Pahrump(some 12 year's later) we stayed at Desert Treasure(not much shade, all back top), it was 110+ and I now had the same MH but with 15000 BTU airs but no thermostats so they were running on Hi all the time. The lowest temp I saw during this trip was 59 degree's with outside temp's at 110+. Say what you will, all I can say is the MH must have some darn good insulation and NO slides.

 

I've seen people get into arguments over the 20 degree estimate less that outside air(but we all know now that it's ambient air going into the conditioner). If I had to camp/RV at a mere 20 degree's less than OUTSIDE temp's, I wouldn't RV in any hot area's at all!

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