13.5 AC versus 15.0 K AC

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.

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.

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.

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.

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.

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...

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.

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

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.

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