Frustrated with this A/C problem

[Thurman]

If you searched previous posts I have made you will find that I have had problems with the Dometic 15,000 BTU A/C units on my Coachmen Freedom Express 310BHDS. I am now on my third unit since the original purchase January 2015 with the last unit being installed August 2016. We got home this afternoon from a four day trip to Florence Marina State Park Georgia which is somewhat mid-Georgia on the Georgia/Alabama line. We had a nice shady spot with a little early morning sun but shade most of the day. Friday afternoon at 3:00 P.M. the outside temp was 89* but inside the TT was at 81* with the A/C unit running wide open, so to speak. I had the door to the bunk room closed as well as the doors to the front bedroom, so we were essentially cooling only the living/dining areas. I intentionally took my nice, not a toy, laser thermometer with me as I expected a problem. With the inside temp at 81*, the air going into the A/C unit was measured at 82*, remember that the air at the ceiling is a bit hotter. The air coming from the unit was a steady 64*-66* with the "quick cool" damper open. I built and installed a box that prevents the cooled air from returning back to the incoming air, there is about 12" separation of the air now and I do believe that it has helped. I have also installed a hygrometer to measure the relative humidity in the unit and it was at 59%. Last week with the TT hooked up in my backyard I tried using a de-humidifier I had bought some years back for the house but it put out so much heat it was ridiculous. Saturday at the CG wasn't any difference but thankfully there was a nice breeze blowing so we could sit outside. That's when I noticed that the TT in front of me was a "Salem by Forest River" unit with two slides on the back side, appeared to be similar in length to mine and had one, only one, Dometic A/C unit on the top. When the owner got back I went over to introduce myself and to ask him if his A/C unit was cooling his TT. Well, he also had a front slide and his unit was a 31 footer as is mine. His floor plan is almost the same as mine except he has a slide for his sink, range, and fridge which technically gives him a bit more square footage than mine. He invited me inside and his unit was a nice 74* which is where he had his thermostat set before they left on an errand. His unit was a 15K Dometic ducted unit as is mine but his was cooling his TT much better than mine would do. I invited him over to look at mine and showed him the temps on certain objects within the TT and the incoming and discharge air at the A/C. He was quite perplexed, to say the least, as to why my TT would not cool down. We had some friends who were camping with us and he has a 26 foot Jayco with a Coleman unit that will run you out with cold air. We all three seemed to agree that maybe my unit was built without any insulation in the roof or walls. I know this is not true as I had to remove both the skylight and vent in the bath area to run some wiring for an extra bath light and there was barely 3/4" of insulation in the attic. While I had the inside cover of the skylight off I added two layers of window tint to help keep out some of the sun and heat, it did help. At one time I removed all of the ceiling registers and found that all of them had gaps allowing cooled air into the attic and taped the gaps up. I also check to see if the ducting was open on either end and sure enough the rear duct was open into the attic. I plugged up that gap also. As far as the walls being insulated, who knows. I have been trying to decide on adding a second unit over the front bed as there is a vent there and this weekend seemed to tip the scales in favor of the second A/C unit. I just cannot understand how the Salem TT was so much cooler than mine with the Salem cooling just a bit more square footage and having practically the same 15K unit as mine does. There, I'm done venting and open to any suggestions as to how to solve this problem.

[Super 8]

I have a friend across town with the same floor plan as mine in a different company, Dometic 15K AC with no complaints. He helped me lift my second AC onto my roof over the front bedroom last week. He was shocked my 15K doesn't cool my camper alone.
My Coachmen has white EPS insulation in the walls, EPS has the lowest average R-value of the three types of rigid-foam insulation, around R-4 per inch.

[LeoS]

One more thing to check before you give up on your Dometic AC unit… When you pull the main cover off from the ceiling inside, take a look up inside there should be a 1 inch thick rubber/foam divider separating the cold air outlet from the warm air return. In my case it was cut too short, allowing cool air to bypass directly up into the return side without cooling off the trailer. I used HVAC metal tape to seal off the gap. Big difference for me.

[rockfordroo]

Also make sure that the openings from the cold air plenum into the ducts is wide open so you are getting full air into the ducts. Ideally the passage should be as wide as the cold air plenum.

[Iwannacamp]

There are many complaints here about Dometic A/Cs built in the last few years(as I am sure you know). The contractor that was manufacturing the coils made some sort of errors and caused failures. I read a bulletin about that and the "problem" should have been corrected after June/July of 2016. I would check the info. as suggested here, but if the problem has only recently started then you may have lost some capacity/refrigerant charge. I think the leaks are slow because the charge would be small and normally aren't completely empty of charge...just low. You can check the temperature drop across the evaporator coil and see if it is running at normal capacity. The normal temperature drop should be 18-22 deg. temp. drop between supply and return air with the system in normal operation, high blower speed, ducts all open, trailer at 85 or less(but not 65), coils/filter clean, etc.

[325BH]

Insulation (or lack thereof), slide outs, darker colored camper, etc. are all contributing factors of needing more ac tonnage.

I have a 38' TT that I finally installed a 3rd ac unit in. The two factory ac units were favoring the front of the camper. Even though two ac units might have been enough if the were better located, they would not cool the bunkhouse as they were.

With three I am golden in any temp. When temps get over 90 degrees, it can take a lot to keep a camper cool.

[Iwannacamp]

Originally Posted by 325BH

Insulation (or lack thereof), slide outs, darker colored camper, etc. are all contributing factors of needing more ac tonnage.

I have a 38' TT that I finally installed a 3rd ac unit in. The two factory ac units were favoring the front of the camper. Even though two ac units might have been enough if the were better located, they would not cool the bunkhouse as they were.

With three I am golden in any temp. When temps get over 90 degrees, it can take a lot to keep a camper cool.

X2

[325BH]

I'll also add...

Now that I have three air conditioners, I no longer use the ducts, I use the dump on the main unit. (The other two are dump only.) That really helps, because the ducts are a huge bottleneck... even when they are working correctly.

The ac units work much better in dump, although that doesn't deliver the air where you want.

[dwayneb236]

And in my trailer the dumps are kinda loud. But I do like using them to cool quickly.

[Thurman]

"LeoS": The original Dometic unit, which I am on my third one now, has the older style metal plate that divides the incoming and outgoing air. I've had the air distribution box off so many times the image is embedded in my old feeble brain. The new Dometic unit which I installed last Wednesday (June 28) does have the newer style laminated styrofoam/aluminum divider. We just got back from a five day trip to High Falls State Park Ga. and the extra A/C unit almost was the answer to my problem. I say almost as Saturday afternoon the outside temp got to 92*, the sun was directly on the street side of the camper and with both units running the inside temp got to 79* for maybe two hours. I monitored both units for air going into the unit and coming out of the units. The original unit was running pretty constant with a 15-17 degree differential and the new unit was hitting a 17-19 degree differential. At night I would turn off the new unit and the older unit would keep us comfortable. Interesting note: I used a hole saw to cut the hole into the outside wall to place my electrical connection for the new A/C unit. The plug I removed shows how the wall is laminated. There is the fiberglass outer skin which is maybe 3/16", then one inch of stryrofoam, a very thin metallic looking layer which does not attract a magnet, then the 1/8" inner wall layer. Not very efficient as far as insulation.

[kcmusa]

I have the grey wolf, about 33 feet long. my ac was replaces early this year. This 4th holiday we were in MD and the outside temps were in the 90's. My single 15K unit did OK.
Only when the wife fired up the stove did the temps climb.
Dont know what to tell you, just that it should keep you cool.

[Gsxrgrizz]

Participating out of interest.....I have a new 2017 Coachmen 392 MBL 5th wheel and am having some issues with my A/C as well!!! Today it was only 79 degrees here so I tried my A/C for the first time but after running it straight for 2 1/2 to 3 hours the inside temp went from 81 to 77 in the main area....the bedroom up front was still brutally hot!! My old unit (37 foot TT) would have dropped that many degrees in 15 min!!!!!

How much of a difference does a 2nd A/C up front in the bedroom make and ballpark roughly how much does it cost?

[Super 8]

Originally Posted by Gsxrgrizz

Participating out of interest.....I have a new 2017 Coachmen 392 MBL 5th wheel and am having some issues with my A/C as well!!! Today it was only 79 degrees here so I tried my A/C for the first time but after running it straight for 2 1/2 to 3 hours the inside temp went from 81 to 77 in the main area....the bedroom up front was still brutally hot!! My old unit (37 foot TT) would have dropped that many degrees in 15 min!!!!!

How much of a difference does a 2nd A/C up front in the bedroom make and ballpark roughly how much does it cost?

I just installed a new 13.5 AC Dometic unit to my front bedroom, it makes a huge difference! Dropped the bedroom temp 20 degrees in less than 10 minutes. Expect $5-600 if you do it yourself. Note, it was 85F in the camper 10 minutes prior to this pic.

[Thurman]

Super 8's post is what I would have replied with one difference. I installed the 15K unit with the same air distribution box (ADB) as his is. In another post I made I stated that we had one problem during our five day trip to a State Park with controlling the inside temp. That was due to direct sun beating down on the street side of my TT. At one point a thermometer mounted on the inside wall of the large slide was reading 91*. But as I stated the sun was directly on this wall. Overall the addition of the second A/C unit was a positive move. The fact that I installed the 15K unit instead of the 13.5K unit was additional cost, some pocket change back from $700.

[Super 8]

Originally Posted by Thurman

Super 8's post is what I would have replied with one difference. I installed the 15K unit with the same air distribution box (ADB) as his is. In another post I made I stated that we had one problem during our five day trip to a State Park with controlling the inside temp. That was due to direct sun beating down on the street side of my TT. At one point a thermometer mounted on the inside wall of the large slide was reading 91*. But as I stated the sun was directly on this wall. Overall the addition of the second A/C unit was a positive move. The fact that I installed the 15K unit instead of the 13.5K unit was additional cost, some pocket change back from $700.

Thurman, I would too have purchased the 15K unit but I was fighting space of where the hole needed to be cut near the bathroom vent.

[scootingranny]

We had one of the bad Dometic a/c units that was replaced under warranty. The ac guy said that our unit was taped better than most but that it would be a good thing to check all the vents. We got busy and just never followed up until one day when the ac was running, we heard a rattling type sound from one vent. This is what the problem was...the solution was cheap easy and the results were amazing. http://www.forestriverforums.com/for...ac-127385.html

[Thurman]

"scootingranny"- -That is exactly what I found when I checked all my ceiling registers. I also used the metal foil tape to seal around each of the ceiling registers as you did. At times I have wished I could rip off my roof to examine how the ductwork has been installed in the ceiling area, I'm betting the joints are not taped at all.

[scootingranny]

Originally Posted by Thurman

"scootingranny"- -That is exactly what I found when I checked all my ceiling registers. I also used the metal foil tape to seal around each of the ceiling registers as you did. At times I have wished I could rip off my roof to examine how the ductwork has been installed in the ceiling area, I'm betting the joints are not taped at all.

We almost got to find this out last week when a storm blew through our campground...no damage except a piece of trim popped off and DH was able to pop it back on. But I bet you are right!!!