13.5 AC versus 15.0 K AC

[TomG2]

Dealer has two travel trailers that are exactly the same except for the air conditioner units. Any disadvantage to the 15.0 k models? Early freezup etc.? Either will be adequate for the trailer as it will be parked under a carport. I have a similar model with the 13.5 unit and it does very well. The 15.0 k model is the same price, so the only question is about efficiency and potential problems.

[TomG2]

I don't spend the heat of Summer in South Texas. That's why my home is on wheels. Either unit will be more than adequate for my use.

[MEXICOWANDERER]

It's a complex interdependent set of calculations but in a nutshell extremely humid air needs a multi-stage evaporator or enough airflow through an evaporator to keep the surface of the evaporator coil above 32F

This cannot be achieved when moisture laden air is passed over a collector at less than freezing temperature. An A/C unit set on high fan will freeze slower than the same unit operating on less air flow through the evaporator.

In my environment it is counterproductive to try to force the A/C to do more than it's designed for...

The largest model dehumidifier extracts as much water as is feasible. The A/C is set on highest fan speed. When R/H lessens to <55% the dehumidifier can be shut off and the AC is left to continue to reduce air temperature into the high seventies.

Generalizations as offered by your dealer are worthless. In full sun near 105F and humidity >60% THREE TIMES the BTU are needed compared to 90F and 40% R/H

I am comfortable in 90F temps with 60% R/H.
Some folks cannot tolerate ten minutes at these values.

I keep harping on it but SHADE is the key. I had THREE roof 13.5K operating on a diesel genset and when I had a palmetto leaf shelter built for shade I reduced the AC units to one. This was in Quintana Roo. Outside air temp 105+F with humidity near 100% (condensing). Near lethal numbers.

[ctilsie242]

Depends on the length of trailer. My 15k BTU A/C does a so-so job at cooling down my rig, come the Texas summer, and my rig is about 27 feet from ball to bumper, without slides.

Here in Texas, if the rig is over 24 feet and has slides, it needs a 15K BTU AC. If it is over 30 feet, it needs two A/Cs, preferably in a "H" design so either A/C can use all the ducts.

If someone tells you otherwise, they are fibbing. Texas is not getting any cooler come summer, so the last thing you want to skimp on, is A/C capacity.

[TomG2]

Here is the quote from the dealer's email:

"We have ours equipped with the 13.5K BTU A/C. We have found the 13.5K BTU A/C to be adequate for that size trailer even in Texas. We have found that the 15K BTU tends to freeze up and stop working on this size trailer, while the 13.5K BTU A/C continuous cools the RV and does not freeze up."

He does not know that I am shopping another dealer.

[MEXICOWANDERER]

It would not be rational to assume one of the major's appliances to be better without being substantially more expensive per unit of size. Some brands may be better than others (understandable) but for a manufacturer to offer a bigger-is-better without a huge price increase is to me not something that is going to be found in a roof air. The same compressor manufacturer is used, the same controls, the same fan motor.

[ford_truck_guy]

I am almost 100% sure the dealer is telling you that because it is what HE HAS on the lot... I am sure that if it were a 15k, he would be telling you that you should never go lower...

[TomG2]

MEXICOWANDERER wrote:

Are you perhaps thinking a larger unit would not work as hard?

What I am asking is if there is any validity to the one dealer's assertion that his unit with a 13,500 btu air conditioner is "better" than the other with the 15,000 btu version. Either will be adequate. Sometimes "Bigger is better", occasionally that is not the case. I am not a RV tech but understand most things technical or mechanical.

[MEXICOWANDERER]

Shade makes all the difference in the world.

Are you perhaps thinking a larger unit would not work as hard?

Down here a 20 qt dehumidifier will bring down relative humidity 15 points over a straight A/C temp drop. It's magic for comfort.

20 PINT

[TomG2]

dougrainer wrote:

You want info, but from your tone you are becoming a jerk. I ASKED questions because I probably have MORE knowledge and info than anybody on this forum. If you ONLY camp at an RV park that ALLOWS you to install carports and it will only be at that park with a Carport, then do want you want to do. There is NO difference in reliability between a 13.5 and a 15. The reason I ask some questions is, there is a BIG difference between cooling a standard box trailer and a trailer with a Slide room. The slide room adds Sq. Footage that most Rv'ers never think of. I would ALWAYS install the largest capacity AC unit unless it was in a trailer less than 21 feet. You state you do NOT need more capacity. But what happens if you camp somewhere where you do NOT have a Carport cover? Doug

If a 13,500 btu air conditioner is adequate for my current 8 X 26 foot box, I think it will be adequate for my next 8 X 26 foot box. I know about slides. I know about fifth wheels. I know a jerk when I hear from one who brags about his infinite knowledge. I simply wanted to know if there was any inherent advantage/disadvantage between to the two units. Where I park in the summer or fall is irrelevant. The only time I park in a really hot climate is when I am under the carport. I know the difference between Minnesota in May and South Texas in July. Thanks for your comparison but not for calling me a jerk. I know what I want to know. You answered it once and then took off in ten different directions.

[dougrainer]

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[TomG2]

dougrainer wrote:

Explain further. You first stated the unit would be under a carport. Then you stated an RV Park, and I am not aware of RV parks that have covered slabs for Rv'ers. State what size and type RV you are comparing. Does it have Slide room, or more than 1 slide room. Are they BOTH ducted? Doug

I won't bother sending a picture, but several of us in this park have carports over our RV's. Took the roof temperature from 135 degrees down to 95 degrees when I installed it. Not sure what difference it makes, but it is a no slide travel trailer and I will add that the box measures 26 X 8 since you seem to feel that is important. Either unit will cool the trailer as that is what I now have with a similar trailer. The ONLY difference is which AC unit is most likely to be trouble free. Here is the deal: A 13,500 btu air conditioner does a good job with my current 26 foot no slide trailer. I do NOT need more capacity, just the best unit for the same price. Both units are ducted with wall thermostats. You seemed to prefer the 15.0 K unit in a previous post. Are you having second thoughts?

[dougrainer]

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[Bumpyroad]

TomG2 wrote:


2-13.5's is not an option. Where did that come from? One unit of either size will be adequate under my carport. I am only interested in hearing if there is any advantage/disadvantage to a Dometic 13.5 unit versus a 15.0 model. Power consumption is not a factor as I will be in a RV park with adequate wiring.

terribly sorry I posted a suggestion on what I would consider to be a "better" set up. I think if I was doing it I would consider a two ac setup, invest that $150 on installing a second AC. I found it nice to have two aCs front and rear, during day could cool unit then switch front noise off, and the opposite at night, run the front one.
bumpy

[TomG2]

dougrainer wrote:
1. For ANYBODY to suggest a larger AC is prone to freeze ups shows they are LYING.
2. The operational controls are identical
3. The 15K will pull about .8 to 1.2 amps MORE than a 13.5k Depends on the model
4. How comfortable you will be in a 13.5 versus a 15k is subjective. Everybody has different levels of comfort
5. In 38 years as an RV Tech, I have NEVER had a customer complain that they wasted money on a larger AC unit
6. In 38 years I HAVE had customers complain they wish they had the LARGER AC unit. Doug

Thanks for some facts instead of questions.