A/C Question

daveinfl · 08-19-2015, 09:46 AM

A few weeks back I saw a question about humidity in the TM. Last year (our first real year with the TM) we didn't notice it. This year we are.

I have kept the filters very clean. I have removed the cover from the inside and cleaned everything. The A/C will take our 95 degree 2619 and cool it down into the low 70s (or more) quickly. But when it cycles, now we are feeling moist air.

In fact it almost seems the inside of the TM is always humid. Our TM has a Carrier Air V in it. Just wondering, does it recirculate the air to cool or draw air from the outside?

Thanks,

Daveinfl

Oh. PS we are in Connecticut right now. It is hot and humid out up here. But it is a beautiful State.

Padgett · 08-19-2015, 10:00 AM

Mine is a Coleman and it recirculates but also the fan runs even if the compressor has cycled. Just the moving air makes you feel cooler.

Don't forget that as the temp goes down for a static amount of moisture, the humidity goes up so the coils need to drain outside the coach

klpauba · 08-19-2015, 11:16 AM

This is typically due to an oversized A/C. If the compressor doesn't run for more than 15 minutes (or so), little humidity condenses out and drain even though the real temperature has been reduced to the setpoint. In fact, the residual condensate might still be on the evaporator/cold coils and/or drain pan when the compressor stops. The constantly running fan just humidifies the air once again.

If it were a home, the options are 1) a replacement of the A/C that more closely matches the load; or 2) the addition of a (whole-house) dehumidifier.

Some will open a door or window to increase the cooling load. Sure, that makes the A/C run longer but the make-up air is drawn in from the outside so it doesn't really decrease the humidity.

It's probably not feasible but I wonder if there's a way to use the built-in heat strips to increase the cooling load without adding humidity? It would be a way to make the A/C act as a dehumidifier. Granted, it would increase the electrical load and, thus, be viable only if there's electrical hookups (and you're not paying by the kWH).

Padgett · 08-19-2015, 11:39 AM

Since I live in a very humid climate and do not have the issue, my first thought is a clogged drain making the AC act as a humidifier.

tentcamper · 08-19-2015, 02:41 PM

Quote:

Originally Posted by klpauba

This is typically due to an oversized A/C. If the compressor doesn't run for more than 15 minutes (or so), little humidity condenses out and drain even though the real temperature has been reduced to the setpoint. In fact, the residual condensate might still be on the evaporator/cold coils and/or drain pan when the compressor stops. The constantly running fan just humidifies the air once again.

If it were a home, the options are 1) a replacement of the A/C that more closely matches the load; or 2) the addition of a (whole-house) dehumidifier.

Some will open a door or window to increase the cooling load. Sure, that makes the A/C run longer but the make-up air is drawn in from the outside so it doesn't really decrease the humidity.

It's probably not feasible but I wonder if there's a way to use the built-in heat strips to increase the cooling load without adding humidity? It would be a way to make the A/C act as a dehumidifier. Granted, it would increase the electrical load and, thus, be viable only if there's electrical hookups (and you're not paying by the kWH).

Once you get the camper cooled down, try running the AC on low. I think the AC compressor will cycle about twice as long?

klpauba · 08-19-2015, 03:59 PM

Quote:

Originally Posted by Padgett

Since I live in a very humid climate and do not have the issue, my first thought is a clogged drain making the AC act as a humidifier.

You're most probably right, Padgett. Now that I see that daveinfl is, in fact, from FL I can trust what he says is hot and humid indeed is.

Regardless, the 13,500 BTU A/C (1+ ton) is oversized for essentially a ~100 sf living space. Especially with the good insulation provided with the TM. I'd bet a 9000 BTU unit would cool it wonderfully and keep the humidity under control (it would be easier on a generator too). I see Coleman makes the Polar Cub 9200 BTU unit (http://www.adventurerv.net/coleman-p...oner-p-76.html) but the price doesn't reflect the reduced cooling capacity.

An inverter-based mini split unit would be nice also however it would take some engineering work to figure out how to install it.

**wbmiller3** · 08-19-2015, 07:01 PM

I'd love to try one of those inverter units. Saw them everywhere in Australia.

My replacement side AC was 10K BTU, larger than what the factory put in (original factory unit was 7K). It works well in our 2619 if you use a floor fan to blow the cool air around.

daveinfl · 08-19-2015, 07:21 PM

Thanks everyone. I did a little reading on RV A/C and it said you could get humid air from the coils and cooling fins being gunked up. Apparently the dirt can hold water. And that is what we want to get rid of. Tomorrow I will go up topside and remove the cover. From what I have read, that is the only way to access the cooling fins and coils. I plan to clean them and see if that helps.

I will post the end result.

Padgett · 08-19-2015, 09:33 PM

Probably the most humid was at Sebastian inlet last year rained off and on, sometimes horizontally all evening & recall a steady stream of water from the AC on the roof down the street side. I just run on low all of the time & that moves a lot of air with the new lower assembly. Did fog some windows on the outside.

ps the coils you see when the cover is off is the condensor and not the evaporator, that is under the sheet metal and sealed from the outside.

pps why a good idea to keep the filters intact and clean.

ppps one I would look at is the 11,000 btu Mach I Power Saver - run current is about 3A less than my Mach III & LRA is 13A less. Much easier to run on a single generator. This is a newer design than the Polar Cub.

BTW I figure my 2720SL at 160 sq.ft. not 100. 6'6"x24' inside when open and the Coleman Mach III 13,500 will pull below 70F even on a 90+ afternoon in the sun

daveinfl · 08-20-2015, 06:57 PM

Thanks again for all of the responses.

Here is what I found. When removing the shroud on the outside I really didn't see a problem. I did spray the coils with foaming coil spray and rinsed them. I was surprised at no rust at all on the AC unit. But I did find ordinary dirt and a little mold which I cleaned.

Next I began removing the shroud that reveals the evaporator coils. This is where I found the problem. In the front of the AC unit are two very long and tall bolts. My guess is that these are used to torque down the unit and allow it to be used on a variety of RVs. Their are indentations in the shroud for the bolts to fit in. The problem was that the bolts were way to long. About 3/4 of an inch too long. This prevented the front latch clips to properly close. It also allowed about a 1/2 inch gap allowing warm humid air to constantly sucked in. That is why when the condenser cycled off ... I would feel warm humid air coming in. Hence my question at the beginning of my post.

So I drilled through the indentations in the shroud and the then it fit tightly. I cleaned everything before putting it back together. I cleaned the fans, coils and all the dirt and mold. Then I found two caps, filled them with a silicone caulk that would harden but remain pliable, and capped off the tops of the two bolts on the shroud.

The AC unit is now running. I had it on maximum and first and it brought the humidity down to about 45 percent. It was never below 75 percent before. I just went out and turned the temperature up to about 74 degrees and will let it run for a day or so. All drawers and cupboards are open to draw out the dampness. I think this solves my problem.

I have attached a couple pictures so you can see what I mean about the bolts. I would recommend checking this if you are having humidity issues.