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Old 02-17-2019, 09:29 AM   #1
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AC not removing humidity

Folks I'm in Florida for the first time and my AC is not removing moisture from the air. It cools fine except no moisture removal. I have an 2016 APEX 215rbk with a fairly standard Dometic AC.

Is this normal or is there a possible vent line on the roof unit plugged up or sealed up from factory?

I have a couple of temp/humidity gauges lying around because I am usually concerned with low humidity on previous travels in the Rockies, where its typically quite dry, especially in the fall inside a camper. The relative humidity reading actually goes up as it cools down here indicating little/no moisture removal. I've used the AC a few times but only in a dry climate so it might have been acting this way from the beginning.

I've been using campground showers and have done no cooking on the stove to contribute to moisture. I even leave my towel in the car to cut down on water in the trailer.

If its a vent line on the roof unit, any idea what I should be looking for? Do I need to take the cover off? Thanks.
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Old 02-17-2019, 10:41 AM   #2
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When I'm in FL and other high humidity areas the water coming off the roof is quite substantial compared to drier climates (some places no run off). Maybe you should remove the shroud (cover) and have a look see. Remember though the AC is not exchanging outside/inside air and any openings to the outside don't help.
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Old 02-17-2019, 10:45 AM   #3
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No need to tell you Florida humidity is crazy tropical compared to what you are used to. I would compare your hygrometer reading inside to what is outside. If your inside reading inside is below 70%, I'd say you're not bad. 55% would be ideal. If you have condensate dripping off roofline from A/C unit, which is what I would expect in Florida, I'd say it is working.
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Old 02-17-2019, 05:59 PM   #4
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Assuming it's just the Florida humidity and your A/C is working ok, you way want to look at one of the smaller dehumidifiers (say a 30 pint model?). They are not expensive and only run on about 3.5amps of AC power. You could attach a short hose and just sit it in your shower to drain into the grey tank when hooked to power and sewer.

It probably also depends on how we used our trailers as to how much extra moisture *WE* are adding to the air from showers, cooking, and just breathing. Start with 98% and up in Florida and that's a lot to ask from a roof top A/C unit.
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Old 02-17-2019, 09:32 PM   #5
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be very sure unit is closed up. Roof vents all closed? Windows all closed? No outside air intrusion.
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Old 02-17-2019, 09:35 PM   #6
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Use a laser temp gun. measure return air and supply air 18 to 20 degrees differential is all you can expect.
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Old 02-17-2019, 09:56 PM   #7
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If cool air is coming out of the vent then moisture is condensing on the cooling fins inside the AC unit... where is the condensate going from there? Well you will have to crawl up on the roof and take the top half of the shroud off and take a look... My condensation flows out onto the roof and drips toward the lowest part of the roof and out the gutter spout.

BUT it is not possible to get cool air out of the AC without making some water come out of the air.
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Old 02-17-2019, 10:01 PM   #8
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Welcome to the south! You are in a humid environment where the relative humidity is high. When the air is cooled, the less water it can hold. As a result, the relative humidity will rise because the air can not hold as much water. If you are getting condensation running off the roof from the A/C everything is probably working as it should.
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Old 02-17-2019, 10:52 PM   #9
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What humidity levels are you reading..
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Old 02-17-2019, 11:02 PM   #10
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Been living in Florida forever. This is not humid. If you think so just come back in August or September when it is.
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Old 02-18-2019, 03:22 AM   #11
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Been living in Florida forever. This is not humid. If you think so just come back in August or September when it is.
X2
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Old 02-18-2019, 07:33 AM   #12
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TIME is required to lower the humidity in any space.

IF your AC only needs to run a few min to keep the interior temps cool the unit is too large for the RV.

IF it runs 15-20 min or more on each cooling cycle you should be fine.
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Old 02-18-2019, 02:26 PM   #13
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AC units do not normally remove interior humidity because they just circulate and cool the inside air. The condensation that is running off your roof is from the condensor. It is totally outside of your unit. The only way to reduce the interior humidity is to get a dehumidifier and run it inside. PS dont forget to empty the catch basin on it.
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Old 02-18-2019, 02:28 PM   #14
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Been living in Florida forever. This is not humid. If you think so just come back in August or September when it is.

So true !
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Old 02-18-2019, 02:31 PM   #15
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AC units do not normally remove interior humidity because they just circulate and cool the inside air. The condensation that is running off your roof is from the condensor. It is totally outside of your unit. The only way to reduce the interior humidity is to get a dehumidifier and run it inside. PS dont forget to empty the catch basin on it.
No or wrong both fit ! the condensation is from the inside evaporator coils not the condenser . it's the inside coils that get cold causing the condensation which is expelled by drains under it leading to out side and off your roof . the AC keeps humidity down inside .
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Old 02-18-2019, 02:47 PM   #16
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[QUOTE=MR.M;2028255]No or wrong both fit ! the condensation is from the inside evaporator coils not the condenser . it's the inside coils that get cold causing the condensation which is expelled by drains under it leading to out side and off your roof . the AC keeps humidity down inside .[/QUOTE

I'll add a little to that. The inside coil that Mr. is referring to is not Inside the trailer but on the roof in the inside portion of the A/C unit. The unit is divided in 1/2. Evap inside and cond outside.

Dehumidifier is needed inside the trailer when the gas furnace is on. Not the A/C.
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Old 02-18-2019, 04:39 PM   #17
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We started running a small dehumidifier in our rv. One of the best things we added to the camper.
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Old 02-18-2019, 08:17 PM   #18
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Put a little extra lift onto the side or end of the trailer that your heads are on when you sleep. The extra lift should allow you to get better roof drainage, If you get no results, get up on the roof and look to see if there is anything obstructing the water flow from the condenser. I live in Florida year round. Outside temperatures above 85 degrees keep humidity about
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Old 02-18-2019, 08:25 PM   #19
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Originally Posted by stillontheroad View Post
AC units do not normally remove interior humidity because they just circulate and cool the inside air. The condensation that is running off your roof is from the condensor. It is totally outside of your unit. The only way to reduce the interior humidity is to get a dehumidifier and run it inside. PS dont forget to empty the catch basin on it.

WRONG.
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Old 02-18-2019, 08:49 PM   #20
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Update

I was beginning to think that the condensate line was blocked, but that is not the case. Also was wondering if it was possible to freeze the line although I didn't think likely at 70F outside. The reason I thought that could be possible is that I tested the AC at home in the summer, 90F outside, maybe 50% humidity and the trailer got down to 57F and the air out the vent was maybe 43F or 47F, can't remember. Thought that might have refrigerant cold enough to freeze the condensate. Brand new Dometic A/Cs really do some cooling(13.5 kbtu on 25 ft trailer).

Late this morning(75-80F out) turned AC off for awhile and restarted it and it dropped inside temp from 75F to 70F and humidity from 80% to 58% in about an hour. However, over time the humidity starts climbing, especially at night. The real problem is that it looks like A/C may not be on enough after reaching temp to keep humidity in check. A/C too strong and trailer too well insulated. So just bought a 35 pint dehumidifier. Seems to be doing the job.

Did some quick calcs, trailer(25 ft) can hold about 1 liter of water in the air at about 68F. So to reduce relative humidity after letting the camper get warm and humid while out in about an hour this unit should do the job. The 35 pint/day is about .66 liter/hr, trailer may be warmer than 68F holding more water than 1 liter in the air, but you only need to get the humidity down to the 50% range for comfort. Of course nameplate number is the maximum rate under some ideal conditions, but should be in the ball park. Also, read somewhere that a person expels maybe a liter per night while sleeping. So take 2 people and the unit running on low may due the job during the night.
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