Expecting too much from AC?

[tim1970]

We took our 5th wheel out last weekend (Jayco 29.5 BHDS) and the campsite only had 30 amp hookups available, so we could only run 1 AC unit. Unfortunately, that 1 unit could not keep up. On Saturday morning when we left the RV it was 68 degrees inside. We were gone the entire afternoon, so the door of the RV was not opened until we got back around 5:00 that afternoon. The temperature inside the RV at 5:00 ws 88 degrees. The outside temperature that day was 102 degrees, and there was no shade whatsoever where we were parked at. It was probably 10:00 that evening before the temperature inside the RV dropped back down to a comfortable level.

My unit is still under warranty, so I can take it in and have it looked at, but before I do, I wanted to get everyone's opinion on whether or not I am expecting too much out of a single 15K unit.

[SugarHillCTD]

pianotuna wrote:
tim1970,

I would try running both air conditioners. Monitor the voltage during the hottest part of the day. If it stays at 107 volts or above you are golden.

Makes me remember a problem we ran into a few years ago while staying in a larger CG. Our normally cold A/C unit just wasn't putting out much cold air.

When we walked around we heard lots of other A/C unit working, including a few big RVs with 3 rooftop units. All that usage was creating a bit of a CG brownout- low voltage.

The OP may have been asking too much of a single A/C unit that was trying to run on less than proper voltage.

We now carry a volt meter to check.

[Cummins12V98]

RV frig turn to propane same with WH. Run both AC's, carry on.

[2oldman]

TXiceman wrote:
DO NOT use an infrared temp gun as it will not read air temperature. It only reads radiated heat from a surface.

Which is most cases is exactly the same temperature as the air passing over the vanes.

[pianotuna]

tim1970,

I would try running both air conditioners. Monitor the voltage during the hottest part of the day. If it stays at 107 volts or above you are golden.

Set one air conditioner at 20 c (68 f) so it will run constantly. Set the other at 22 c (72 f) so it will cycle.

If you are in a dry climate, consider adding an evaporative cooler.

Set the fridge to propane, and turn the electric portion of the water heater off.

Add "pillows" to any vents and skylights. Close the blinds. Use the awning.

[TXiceman]

Addy15 wrote:

laknox wrote:
Rule of thumb is ~20 degrees below ambient is about all you can expect from an RV A/C. Might have done better to close all the slides while you were gone. Less surface area exposed and less cubic to cool.

Lyle

We were talking to someone at an RV dealer (on a completely unrelated matter, but the conversation came around to AC for some reason) just the other day who said not to expect much more than 10-15 degrees below the ambient temp.

Totally wrong. A properly running RV AC unit will cool the outlet air closest to the unit, to 20 degF below the air entering the unit. DO NOT use an infrared temp gun as it will not read air temperature. It only reads radiated heat from a surface.

Ken

[Old-Biscuit]

2oldman wrote:

Old-Biscuit wrote:
The 20 degree difference is between the A/C Unit Return air temp and the A/C Unit discharge air temp....basically the amount of temp drop across the Evap Coil

We've had this discussion a few times and this statement always comes up.

MY experience is that my output air is a constant 55 or so degrees. The best my coach can do with that is to stay 20F below ambient.

If the discharge air were only 20F below ambient it would take a very long time to cool the coach. But, this 'fact' has even been said by people claiming to be HVAC techs, which in my case, is just not true. I've even stuck thermometers in there only to be told they were incorrect. So, according to them, my a/c is either 'defective' or magic.

Delta T

“Delta T” is the most common use of the word delta in the HVAC industry, meaning temperature difference. If the temperature before a cooling coil is 75F and the temperature after the cooling coil is 55F, subtract 55F from a 75F to find a delta t of 20F.

Notice the temps are measure before and after the cooling coil...INSIDE Air temp.
Nothing to do with outside air temp


Outside ambient air temps have an affect on 'heat load' but the Delta T is a measurement of A/C performance.

[Halmfamily]

I feel you on the high temps and struggling A/C on a 30amp circuit. Here on Alabama it gets in the high 90's and 80% humidity. A couple things we did that helped us.
1) Put foil backed vent covers in each roof vent.
2) Paint the outside of your skylight white, still allows light in but helps reflect heat.
3) Get some rolls of Reflextec (Not sure of spelling) foil insulation and cut to fit on the inside of all of your windows.
4) We had slide out toppers installed when we purchased our FW and that helps keep the top of the slides cooler

Hope this helps

[valhalla360]

A simple trick is to close of the bedroom and bathroom area (including any vents feeding it). This allows the single air/con to focus cooling on the living space.

(at night you can switch to the bedroom unit and it should quickly cool it down without the sun beating down)

I figure on really hot days, we can get another 4-5 degrees cooling in the living area.

[RoyB]

My backup plan for something like this would be to always carry a couple of good quality extension cords.

The camping site probably had a 30A service as well as a 20A service. These would be on separate circuit breakers on the pedestal...

I would rig something up to use the 20A service along with the 30A service to get it cooler... i.e. have a portable air conditioner that would plug into a 120VAC standard wall socket and use their 20A service to power tat up etc...

It is also possible to rig up the shore power adapter cords to plug the 30A service into one of the 50A zones and the 20A service into the second 50A zone of your trailer just to run the second air conditioner... Those two 50A zones in your trailer are wired separately...


Google Image

A couple of ideas to look into to see if it might be feasible for you to do in this respect...

I know in my case I really don't need the air conditioners as most of my camping is OFF-GRID Camping running everything off the batteries. I am very happy to only have a couple of those fantastic roof fans running in the early evening and all night playing with the cool night air... If I am at a creekside camp setup I will be in hog heaven haha...

I can't remember the last time we have used our roof mounted air conditioner...

we all have our different way to love the outdoors haha...

Roy Ken

[doc_brown]

I expect at best 20 degree difference between outside and inside when outside temp is 95+, with a 15k unit up front and 13.5k in back of a 3 slide 40ft Class A.

[time2roll]

Ok this is crazy however I would try once to turn off all breakers except the two air conditioners. Start them one at a time and see if both will run.

Secondly remove the inside panel and check the plenum separator is well positioned and well sealed between the Intake and Exit. Often these are poorly installed and cold air just circulates inside.

Always monitor voltage in hot conditions. 108+ volts needed for best results.

[wildtoad]

102 in direct sun then you should be happy.

[ford_truck_guy]

ScottG wrote:

ford truck guy wrote:

BarabooBob wrote:

ford truck guy wrote:
I was just at the beach for 5 days.. Our 42', Mostly DARK outer skin Fifth wheel ran about 75-78 degrees inside while it was 95 outside.. FULL SUN with the front door open, no awning out ( TOO WINDY ) only having a plexi glass PIECE in front of the screens..

We were ok with those results...

We run 2 of the 15k units, and using a digital thermometer, I was getting 59-60 at the vents

Why would you leave the front door open? Isn't that a huge waste of electricity?

Thats why we put theRV Door Buddy
on there... It is nice to be able to have the door open for better viewing.. i would MUCH rather sit and look out an open door..

The DB is going to let a TON of heat in.

It did at FIRST... then I added EZ Snap window screen to the front of the door buddy.... With a digital thermometer I was getting about a 2 degree difference from the inside walls to the inside of the door buddy... BIG DIFFERENCE from original. I thought it was all hype till I tried it..

They claim it blocks 90% of the heat.... not sure of the amount, but I believe its close to that number..

[WTP-GC]

Our GD Reflection is the same size as the OP's rig. With one 15K BTU Dometic AC running all day, the inside temp during a very hot camping trip recently in GA fluctuated between the mid to high 70's. Because I like it cooler, I leave it set on 72 degrees all day and it runs non-stop. At home, stored next the barn in nearly full sun, I leave it set on 77 degrees and the unit cycles on/off throughout the day. We close the bathroom door when not being used and have the insulator pads in all the vent openings, plus the Max-Air vent covers on the outside.

Last trip out, I discovered a 4" round disc in one of the ducts on the rear bunkroom. It was where they drilled the hole for the diffuser and the coupon was left there. Might be more of those elsewhere. I removed it and it helped air flow. I also sealed up all the openings on the interior of the unit where cold air was blowing through into the intake. Did a little more stuff like that and it drastically improved efficiency of the unit. Over on the GD Owner's forum, most people are pretty well convinced that a correctly functioning single 15K BTU unit should sufficiently cool a rig of this size at any campground this side of hades.

So no, you're not expecting too much from a single unit. Its apparently not operating correctly.