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Old 07-14-2003, 10:00 AM   #1
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way too humid!!

I have had this problem with most all of my RV's in the dead of summer. I just got back from a few days in steamy hot San Antonio and at it just gets plain sticky wet inside, especially at night. I got a combo temp/humidity reader and watched it for a few hours and here's what I got, 70 degrees and almost 95% humidity. If you crank the a/c down they will both drop as the compressor comes on but after a while it will get way too cold, almost unbearably cold, then the compressor will cycle off and as the fan continues to blow the humidity zips right back up. I am thinking that most all RV's have the fan wired to run continously and this is what I think causes the extreme humidity. I could wire the fan to run only with the compressor but don't you need the constant airflow to prevent stratification of the air? Maybe I need to get a little dehumidifier? Crack open a window maybe?

I usually deal with large commercial HVAC units and am stumped at this little booger, don't tell me I have too big of an A/C?

Chas
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Old 07-14-2003, 10:24 AM   #2
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Re: way too humid!!

Quote:
Originally posted by Chas
I have had this problem with most all of my RV's in the dead of summer. I just got back from a few days in steamy hot San Antonio and at it just gets plain sticky wet inside, especially at night. I got a combo temp/humidity reader and watched it for a few hours and here's what I got, 70 degrees and almost 95% humidity. If you crank the a/c down they will both drop as the compressor comes on but after a while it will get way too cold, almost unbearably cold, then the compressor will cycle off and as the fan continues to blow the humidity zips right back up. I am thinking that most all RV's have the fan wired to run continously and this is what I think causes the extreme humidity. I could wire the fan to run only with the compressor but don't you need the constant airflow to prevent stratification of the air? Maybe I need to get a little dehumidifier? Crack open a window maybe?

I usually deal with large commercial HVAC units and am stumped at this little booger, don't tell me I have too big of an A/C?

Chas
Got too big of a A/C.


Hahha
Is it possible that it's pulling raw outside air instead of recycling?

Its amazing how much moisture a person expells. With the Aluminum inside there is noting to absorb that moisture.

I have slept in the back of one of my truck in the winter and had a layer of condinsation frozen to the roof of the fiber glass shell almost a 1/4 inch thick (It dropped down to 15degrees that night). I sure wasn't sweating so that had to all come from my breath. I have been told I'm full of hot air a lot so that may have been part of the problem.
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Old 07-14-2003, 10:45 AM   #3
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Chas

You probably know this, but running the fan at the slowest setting will remove the most humidity because the coils get colder. My former house had a humidity control that worked by varying fan speed in this manner.

Beyond that, I really can't help you since I haven't had a humidity problem except when it is right at the outdoor temperature where the AC doesn't run enough to remove the humidity and it is too warm to open the windows..
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Old 07-14-2003, 10:49 AM   #4
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Welcome to the South. Unless by buy a de-humidifier (that puts the heat back into the trailer instead of dumping it outside), it will get very cold using the airconditioner. I just use plenty of blankets to cover up with. I hate humidity. I would rather freeze.
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Old 07-14-2003, 11:10 AM   #5
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Well, yes...

... your a/c is too big. More info on problems with an a/c that's too big is at http://www.proctoreng.com/articles/bigger.html

But there's not much you're really gonna be able to do about it, so let's talk about how to live with it.

First of all, don't run the fan unless the compressor is running. The fan just re-evaporates mositure back into your trailer when the compressor is off. Use a separate floor fan or something if you feel like you need the circulation.

The second thing you can do, and yes this sounds strange, is to heat the inside of the trailer artifically to make the a/c run harder. This is what happens automatically with your car when you turn on "defrost" - the a/c comprssor turns on with the heater, and you get warm and very dry air. Some kind of electric space heater, maybe? A little help from the furnace, even? If you're paying the utilities, use the furnace. If you're at a utilities paid space, get an electric heater.

The usual warnings and admonitions apply - use a proper cord, don't overload circuits, don't try this at home, your mileage may vary, and your mother warned you about this.

If it make you feel any better about what probably sounds like wacky advice, I'm a Registered Professional Engineer and I've been in the a/c and energy business for 30 years.
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Old 07-14-2003, 12:34 PM   #6
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I told ya'll not to say I had too big of an A/C!!,

As far as the a/c unit goes it is the original Armstrong, not sure on the BTU rating but evidently it kicks butt!! Never thought I'd have to worry about too much cooling. I will look at the wiring diagram and see about wiring the evaporator fan in with the compressor and the condenser fan. (Armstrongs have separate condenser and evaporator fan units) The only thing I may worry about is the startup amp draw, having the compressor, condenser and evaporator fans all hitting at the same time. I have seen some dehumidifiers at Lowe's but really hesitate to have to drag one along, maybe I could build it in somewhere if I got one small enough? Sears maybe? Maybe just wait for
winter??

Chas
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Old 07-14-2003, 12:37 PM   #7
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OK, your a/c is NOT too big!!

...Your trailer is too small!

Feel better now?

I'm absolutely serious about running the furnace. Try it and see.
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Old 07-14-2003, 12:46 PM   #8
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Maybe

I get tired of the constant fan noise. Maybe the fan could be simply dropped back to a lower speed when the compressor is not running, It would just take a triac and a few components and a bypass from the compressor circuit. Less of a startup requirement that way.
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Old 07-14-2003, 01:02 PM   #9
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My SOB that I had before the A/S cycled the airconditioner fan off when the thermostat set point was reached. That made a big difference in the humidity control. I would hesitate to say that your airconditioner is oversized because you have to understand that you have to be sized to overcome the heat gain when you are in the hot climes in full sun conditions. Unfortunately your A/S is not insulated as well as your home which means that what may be right for daytime, might be a little over for night.

I do have a link somewhere ( I think it was on this forum) with some detailed instructions on how to convert your air conditioner with the constant on fan to one which cycles with the thermostat. I'll try to find it and post the link. Personally the process was a little too big for me to handle.

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Old 07-14-2003, 01:05 PM   #10
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Re: Maybe

Quote:
Originally posted by Pahaska
I get tired of the constant fan noise. Maybe the fan could be simply dropped back to a lower speed when the compressor is not running, It would just take a triac and a few components and a bypass from the compressor circuit. Less of a startup requirement that way.
The only problem with that John is the possiblity of freeze up. I talked an a fellow who handles RV A/C repairs in the Destin Fla area. He says it is quite common to get calls for frozen condensers when humidty is very high and folks dial down the fan speed to low.

Jack
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Old 07-14-2003, 03:42 PM   #11
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Chas,

I have experienced your situation myself. We ran the furace and the AC the same time, it works. You may get some stange looks from other campers.................

The idea to wire the unit so the fan and compressor work together is a good one, some models of Airsteams had this, others did not. It depends on the model of Armstrong you have.

If you were to wire in an additional relay that would start the fan motor first, and have a delay to the relay to start the compressor you would be fine. This would take the output of the themostat and have it start the blower instaed of the compressor. This is how most home units are set up to prevent quick on-off-on cycling of the compressor.

Even so how do you start your AC normally? Off to low cool, then med, then hi? Is that not the same as just having the whole thing kick on? The biggest drawback I can seee is the noise factor. These old Armstrongs can cool, but they make a racket doing it!
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Old 07-14-2003, 08:09 PM   #12
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I ususally keep mine on high, but I will say that although it may not be as noisy as the older units, it still is a very present noise in the camper.

Other than that, no real humidity issues or freeze ups yet. Of course I've used it only about 5 times in some hot and humid and not so humid heat.

Eric
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Old 07-14-2003, 08:20 PM   #13
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figured it out!

chas

you need to get rid of this thing then your problem will be solved!

john
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Old 07-14-2003, 08:24 PM   #14
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What's that,

The instrument cluster out of a 67 Dodge Polara?

Mine looks different than that, funny and a good try but it has nothing to do with my A/C problems.

Chas
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