RV AC units - Questions

My Roadtrek wrote:

CavemanCharlie wrote:

My Roadtrek wrote:
15 to 20 degrees below the ambient temp. is all you can expect from a 13,500 BTU AC.
This is proved by science.

"The ability of an air conditioner to provide a comfortable environment for the consumer is dependent upon the following conditions.
Air conditioners are rated primarily by their ability to remove heat. The thermal measurement used for detecting a gain or loss of heat is the British Thermal Unit (BTU). One (1) BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. An air conditioner rated at 13,500 BTUH can remove 13,500 BTU’s of heat in one hour.
The ability of an air conditioner to cool down a vehicle or maintain a consumer desired temperature is dependent upon the heat gain of the vehicle. The physical size, the amount of window area, the quality and amount of insulation, the position exposure to sunlight, the number of people using the vehicle and the outside temperature may
increase the heat gain to such an extent that the capacity of the air conditioner is exceeded.

As a general rule, air supplied (discharge air) from the air conditioner will be 15°F to 20°F (11° C to 8.4°C) cooler than the air entering (return air) the ceiling assemblies bottom air grilles.

For example, if the air entering the air conditioner (the return air) is 80°F (26.7), the supply air (discharge air) will be 60° to 65° F (11.1° to 18.3°C). As long as this temperature difference -15°F to 20° F (11° C to 8.4°C) is being maintained at the air conditioner, the air conditioner is operating properly."

Use a thermometer to measure the temp. of the AC right at the vent, if it is 15 degrees, or more below the outside temp, the AC is working correctly, and the cooling problem lies elsewhere, like insulation, air leaks, parking location, type of material parked on, number of people/pets, appliances running, mis sized unit, etc.

Bunk,,, See, somebody wrote in a Science Book somewhere, sometime, that you could not get anything more then a 20 degree drop out of a AC and everybody started quoting it without actually trying it and now we are all stuck with rotten AC units.

My 1993 TT has a Emerson Roof AC that on a 80 degree day puts out 40 degree air as measured by a thermometer stuck in the duct. And, NO ! it does not freeze up!! Now,

that may be because it uses the older type of refrigerant, I can't say.

My last TT had a roof mount AC on it I removed from a camper made in the 70's and that thing would freeze you out.

Also, think of your car. If you were only getting a 20 degree drop in air temps coming out of the ducts on it you would be awful warm on a hot day. Of course, I realize a car AC is a whole different kettle of fish.

I'm talking new AC's here running R134 which is around 19% less effective than R12.
As far as the science being bunk, some people still don't believe in Evolution. :R
Comparing a car AC to a RV roof top AC is comparing apples to oranges. The auto's AC cools better because the compressor spins faster when the viehicle is in motion.

Yes, I did mention that my AC is a older unit running the older refrigerant. I don't know if it was R12 though. That was mostly gone by 93. In any case, that may be the difference, and if it is I will be buying as many as those old units as I can and keeping them for my next TT's.

I did mention that a Auto's AC and a RV's AC is a whole different kettle of fish. I'm not sure the speed of the compressor is the difference though.

My brother has a Coleman Mach unit on the top of his 11 year old 5th wheel. It wasn't working very well and when we checked it out we found there was not way to clean the evaporator. It's inside a metal box, you can't see it, and the box is pop riveted together. Poor design there. But,,, the biggest problem is that when I was on the roof of his RV and had him turn the AC on. I discovered that the fan draws, not pushes, air across the condenser. This also means that that hot air is then trying to be forced out the sides of the unit through those little slots. Also, the hot air is being pushed past the compressor, which is the hottest working part of the AC. What a Stupid, Stupid, Stupid design. No wonder it won't do any more then a 20 degree drop.

I think if there were decent engineers designing these things them maybe they would work better. Even though they are slightly hindered by the newer refrigerants.