AC Humidity

[Karen B.]

Hi, everyone-

Hoping someone can help me troubleshoot here. I had my AC replaced maybe two years ago and it worked great, then I started having issues. (It's a Dometic.) Now when I turn it on, it pumps humidity into the camper, rather than removing it, and it's just miserable in there. At the moment, it's 67% humidity and 66 degrees. I know it's hot in the upper midwest and I know about what an AC can and can't do in those conditions, but this has been happening at much lower temperatures, and every time I turn it on, I just watch the humidity climb on the gauge. Yesterday, when I got set up, the gauge said 25% humidity and as I turned on the AC, I watched it climb to 60% as the interior cooled.

So. What I suspect is that it's not draining, but I can't seem to locate drain holes in the AC itself. Suggestions for what to try to fix this? Trouble shooting? Things to try? Things not to do? Has anyone dealt with this before? Any help would be appreciated--thank you!

[thrifty bill]

If you are not seeing water run down the outside of the trailer, something is wrong.

Dometic manuals are on line. There is a drain pan on the bottom of the AC (outside) with drain hole(s). Water then just runs down the roof.

[gordon2]

Remember that when you say humidity, you mean relative humidity. It's relative to the temperature and because colder air can hold less water vapor, as the temperature drops, the relative humidity increases.

At 67% humidity and 66 degrees (F), the dew point is 55. Consider that at 94 degrees and only 29% relative humidity, the dew point is also 55! Thats fairly dry air and what most people consider comforable.

So it is perfectly normal to see the relative humidity go up when the temperature drops when the amount of water vapor in the air is the same.

I don't think there is a thing wrong with your A/C. If you still think there is then report in the outdoor RH and temp, and the inside values for a few hours from the time you turn on the A/C.

You could have a leak from the condensate but it would trickle in like rain water and not pump moist air in. If there is no leak in the roof then the water will eventually fill up whatever there is and then overflow to the side.

Originally Posted by Karen B.

... Yesterday, when I got set up, the gauge said 25% humidity and as I turned on the AC, I watched it climb to 60% as the interior cooled....

By the way, 25% RH is really low and not likely to be seen in many areas except in the driest part of the winter. I don't trust that gauge.

[Alex Adams]

I know the window unit I use for my trailer, dehumidifies as it cools. Check with Dometic to see if yours is supposed to work the same way. If they say it does, then you have a problem.

[gordon2]

Originally Posted by Alex Adams

I know the window unit I use for my trailer, dehumidifies as it cools. ...

Yes, A/Cs dehumidify but a large roof unit on a small camper in colder weather does not dehu very well, and so the humidity goes up with the drop in temp. If OP will report on the RH when the outdoor temp is about 80 F then we will know if it is working OK or not. I still vote that it is OK.. and RH will be around 50 percent if the outdoor temp is in the 80's ... its just not going to produce a very low RH at 66 degrees.

[gordon2]

PS. Check the inside filter and clean as needed. If only two years old the outside coils should not be very dirty but check them also and clean if needed. Verify the compressor is coming on... the sound is usually pretty hard to miss and the lights might even dim for a second when the compressor comes on.

[Karen B.]

Yes--I suspect this is the problem. There should be condensation running and there isn't any. I haven't been able to locate the drain holes, so I'll be hunting up a taller ladder to get up there.

Originally Posted by thrifty bill

If you are not seeing water run down the outside of the trailer, something is wrong.

Dometic manuals are on line. There is a drain pan on the bottom of the AC (outside) with drain hole(s). Water then just runs down the roof.

[Karen B.]

I did clean the filter inside, which didn't make much difference. I hosed off the outside coils, which also didn't make much difference. The compressor is coming on and I can feel the difference between when the compressor is on, and when the fan is on. So, at least I have eliminated some potential problem points. Onward to the more difficult! Thank you!

Originally Posted by gordon2

PS. Check the inside filter and clean as needed. If only two years old the outside coils should not be very dirty but check them also and clean if needed. Verify the compressor is coming on... the sound is usually pretty hard to miss and the lights might even dim for a second when the compressor comes on.

[redbarron55]

It may be too large of a unit for the camper and short cycles and as a result fails to dehumidify the air.

[Darwin Maring]

Originally Posted by redbarron55

It may be too large of a unit for the camper and short cycles and as a result fails to dehumidify the air.

Thats the best answer so far.

[gordon2]

Originally Posted by redbarron55

It may be too large of a unit for the camper and short cycles and as a result fails to dehumidify the air.

Originally Posted by Darwin Maring

Thats the best answer so far.

Originally Posted by gordon2

Yes, A/Cs dehumidify but a large roof unit on a small camper in colder weather does not dehu very well, and so the humidity goes up with the drop in temp. If OP will report on the RH when the outdoor temp is about 80 F then we will know if it is working OK or not. I still vote that it is OK.. and RH will be around 50 percent if the outdoor temp is in the 80's ... its just not going to produce a very low RH at 66 degrees.

Best answerS so far...

Unless I missed it the OP still has not told us the outdoor temps. An oversized A/C (which they are because these campers are so much smaller than what the A/C is designed for), with a small temperature differential will not remove much moisture at all. But when it gets into the 80's the A/C should make it comfortable.

And I wonder why you are cooling to 66 degrees (F)... I would need a jacket at that temp!

[Karen B.]

Hi, everybody--it's been a minute, but I wanted to update that (I think) I found the problem. This was the summer of fixing a bad ground, replacing the converter, replacing the battery, replacing the AC, none of which fixed the humidity problem (which was still getting up to 85% when I turned it on). My interior lights worked for a little while after I got the converter replaced, but then quit working; the porch light continued to not work. Had issues with the fridge. It was a wild and and annoying and expensive summer.

As I continued to Google the problem, I learned that there was one more fuse that I didn't know existed up at the front of the Scamp. So I went looking for it..and it was MELTED. Melted. Melted! Welp, that explains a lot. Yikes on bikes, that was terrifying to find. Electrical is beyond my capability, so I took it to a local place that was wonderful and he clipped out the melted fuse box and replaced it, and magically the interior lights came back on.

Still no porch light. So we kept digging. Or, they did, and I watched and learned. He brought on a second guy who went digging around in the wires under the seat. Found TWO bad grounds as he was muttering about how the clip connectors are trash (as he replaced them with butt connectors and heat shrink) and once those grounds were fixed, the porch light magically worked.

It's obviously not AC weather, so I haven't checked the AC, but I'm crossing all fingers and toes that this solves that problem too. If the electrical system isn't working the way it's supposed to, no wonder the appliances don't work right. The unfortunate reality is that I replaced an AC that I didn't have to, but Scamp didn't check that particular fuse when they were working on the camper this summer, so they said they'd work to make it right. I hope they do. That would be very kind.

In the meantime, I have what seems to be functional electrics and a lot more knowledge than I did a couple of months ago. Here's to hoping this might help out somebody else!