This is the method I use to check my air conditioner's delta temp.
The normal range of delta, or, the difference between the incoming warm air and
chilled outgoing air is proper as long as that difference is within 15~20 degrees.
If you test your air conditioner using this method, you should achieve similar
results indicating your AC is functioning properly and at it's designed capacity.
The notion of an AC putting out a specific temperature is completely false.

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Checking the delta (difference) temp on your air conditioner is a very simple thing to do and will tell you within a short time whether your AC is functioning properly or may be actually suffering from some minor or even major problem. I use a simple indoor/outdoor thermometer and hang it from the AC near the inlet with a paper clip as shown here. You can see the the temp readings are within 0.7 degrees F. This is close enough for general testing purposes. The little black goodie on the right is the outdoor remote sensor. I purchased this particular unit from Wal*Mart for around $20.00.
Then, I place the remote sensor right in the vent outlet of the AC like you see. In this configuration the main thermometer reads the room (inside) temp, while the remote (outside) sensor reads the AC output Then, all that needs be done is to turn on the air conditioner. I use the high fan setting and set the thermostat to it's coldest setting. Initially, the remote sensor will show a fast drop in temp while the main thermometer will just sit at the current ambient room temp.
When the ambient temp inside the rig begins to show a decrease (as shown on the indoor reading on the top of the thermometer), you've reached a point where you can get the delta temp from the bottom readout as provided by the remote sensor. This reading was obtained after about 45 minutes of cooling inside the rig. You'll notice there's a 23.8 (really 23.1 degrees) degree difference between the two readings and this actually indicates there may be a minor problem. In this particular instance, a simple cleaning of the filters brought the two temps within almost exactly 20 degrees, indicating the AC was performing at maximum operating capacity.

There are a lot of things that can keep your AC from performing like you might expect it to. Insufficient insulation,
limited or no shade, no awning to help you out, too much light coming in, too much area for the AC to cool and
excessive outside temps are the most common problems. These problems are not insurmountable however.

Insufficient insulation is a problem that plagues a lot of older and some of the more newly manufactured rigs.
Unfortunately, there's not a lot you can do to improve this situation aside from 'skinning' your rig, removing the
factory installed insulation, replace it with better, heavier duty insulation and then re-skinning your rig.
For most people this is not a viable answer so, lets look at some that are.

Find shade or make your own!
Park your rig in any shady area you can find with power. This is probably the biggest thing you can do to help keep
your rig cooled down in the midst of summer while running your AC. Of course you'll need power to do it and you'll
not always be able to find shade at the shore pedestal where you can park. So, if you have to park in direct sunlight,
the next best thing is to provide as much shade around your rig as you possibly can. This will help more than most think!
It's not a complete antidote to the situation, but it will help nonetheless. Awnings are great for providing shade.
Parking your rig so the awning is on the sunny side, is always best. If you have separate window awnings, use those too.
If you have a 'screen room' or other portable room, that attaches to the side of your rig, set it up. Be sure to let some
breeze through to help keep it cool however. If you're in an area where the breeze is at a minimum, these enclosed
portable rooms can easily turn into an 'oven'. This can negate the shade area your awning provides by actually capturing
and holding in extra heat right next to the side of your rig that you don't want. You really have to make your own call
on whether to use these or not, but basically, when there's a breeze out, these will help.

Keep vent usage to a minimum!
Keep vent lids open only to a minimum. Crack them open only far enough to let air out. If you see a direct beam
of light coming in, you're letting in more heat. That heat makes your AC work more. Having them open ( a little ) is good
to get fresh air, even with the AC on. With vents slightly open, you're letting out heat as long as there's no light coming in.
If you have a powered vent fan, it's OK to use it but put the fan on it's slowest setting and this will do good to draw
out some of the extra heat. It's important to realize that you should not have a vent fan running hard. I speak here of the
Fantastic Fan and the ShurFlo models which can move a LOT of air in a short time. Leave these fans on the lowest
possible air flow setting, keeping the vent lid cracked open just a little. Not only does operating the fan in this manner
help to draw out heat that's risen to the ceiling, it also helps to mix the warm and cool air inside the rig more evenly.

Keep the light out!
Wherever you see light coming inside your rig, heat is coming in with it. If you have a windshield blanket, use it.
It's good to keep your shades drawn down during the daylight hours which will help, but there's more you can do.
If you just have to see outside, do it from the shady side of your rig so the direct sun doesn't come in.. In lew of this,
apply the 'shiny film stuff' to all your windows. It reflects the light and the heat away from your rig. This is good stuff.
If you can find the kind that goes on the outside of the window, my personal suggestion is to use that type. Reason being
that if you can reflect the heat away before it gets to the glass, the glass will remain cooler. With the type that's applied on
on the inside of the window, the glass will absorb some of the heat. This heat gets transferred to the inside of your rig like
a hot oven with a glass window. If you can't readily find the outside type, just use the inside type. The difference between
them won't make a huge difference, but every little trick that you can do will add up to help more in the overall situation.
In an emergency situation, (yes, there are those situations), apply aluminum foil to the outside of all windows on your rig
with duct tape to hold it in place and while it's a bit unsightly, it works very well!. Aside from being a little unsightly, foil
does have one other drawback. It blocks out ALL the light and can turn your rig into a rolling dungeon. DW may not
be 'in tune' with the aluminum foil idea because of the looks and darkness it creates, so your best bet is likely going
to be to apply the shiny film instead. Please keep in mind, using the shiny film is generally not legal on driver and
passenger door windows! Also, there may be laws in some states that prohibit it's usage on rear windows too.
In these instances, the darker "smoke" film may be preferable to the shiny film. Check your local laws so you know!

Limit the area that needs to be cooled!
As I had mentioned earlier, using a windshield blanket will help to provide an amount of insulation from some of the
heat getting in. This is good, but there's still more you can do to help. Blocking off the cockpit area with screens or
blankets will provide even more insulation from the heat getting to the coach. This works well with class-c rigs as the
cockpit is generally somewhat separate from the coach anyway. Once I'm parked, I'm not using that area so there's
no reason to not block it off. I use a heavy comforter tucked in under the cab-over mattress and leave it hang down to
the floor. This provides a very good insulator from the cockpit and really does work well. Using screens to section off a
particular portion of your rig to limit the area being cooled works well too, but there's a trick to using them and gaining
maximum success. The trick is to seal the top and bottom of the screen so the heat is contained within the sealed area.
The sides are generally not much of a problem, but if the top and bottom of the screen is open to the ceiling and floor, the
heat from the sealed area can seep in from the top opening while your cool air goes in through the bottom. You'll want
to try to avoid this if you can. A strip of Velcro and a short length of cloth or fabric can go a long way to seal things up!

Get the air circulating!
Even when set to the lowest fan setting, air conditioners tend to move a lot of air. Use this to your advantage by getting the
air circulating within the space being cooled. I have found that cooled air moving across the top of the ceiling tends to help
cool the rig faster than if the cooled air is blowing downward. With the air blowing across the ceiling, it mixes better with the
warmer air because the warm air rises. If the cooled air is blowing downwards, the warm air sits at the top of the living space
and can collect in warm 'pockets' where the cooled air isn't circulating. This can sometimes be very noticeable when relaxing
with cool air blowing directly on you and then standing, then suddenly your head feels the warm air at the ceiling. Cool air sinks
to the floor by nature as cold air always does, so rather than pointing the cold air downwards where it will tend to settle, to me
it makes more sense to have it cool the warm air (which is what we're trying to get rid of anyway) as it settles downwards. Also,
try to get the air moving into places where there's poor or little circulation within the area you're trying to cool. The addition of
a couple well placed 12 volt fans can help provide much more circulation than that of just the AC alone. Experimentation with
this will get you the best results but takes time to find the best fan locations within your rig. The 'across the ceiling' technique
works well with non-ducted 'air box' type AC's. Those with ducted AC's will likely have a bit more of a challenge with getting
the air circulation moving across the ceiling. Just remember, you're camping so use your imagination!

Don't use heat generating appliances!
I think this is pretty much self explanatory, don't you? Using your LP oven to bake a pizza at noon while it's 110 degrees
outside is not really a good idea if you're trying to stay cool inside. Microwaves aren't as much of a problem as they don't
create as much heat and don't require preheating or cooling down. Indoor cooking in the middle of the day should be
avoided as much as possible. Use that outdoor BBQ! Hair dryers will contribute a lot of heat to the inside of your rig,
not good! TV sets and other larger electronic devices can generate unwanted heat. I think you get the idea.

So there you have it. Tips and tricks to help keep you cooler during those hot summer months.
I'm sure there's other ideas I haven't thought of yet, but if I do, I'll be sure to include them here.
In the mean time, Happy Camping everyone and enjoy your AC!

Original draft - YoDude 5.27.06