Background, I have a 2018 palomino puma unleashed toy hauler fifth wheel, with dual A/C (351THSS).I took it in almost immediately complaining that the front a/c hardly did anything. They said they fixed it, and it was better, that there was foil blocking the vents. I felt like it still didn't do a good job, but it was getting into colder months and I really couldn't tell.This year as it got hot, it was apparently still sub par. The lesser power unit in the garage does a much better job than the one in the front, so much so that the only way to cool it down is to put a fan in the back and blow it up to the front.I brought it in again before the 1 year warranty was up, and they say it's performing to specifications. I have measured the air temperature coming out of the vent and yes the temperature is good, but it just seems like such low volume it can't keep up.The other night I didn't run a fan from the back to the front, and it couldn't even get it below 80 degrees (this is Central Texas, I would think this is possible at night.So my question, how can I either validate that it's performing to spec, or prove it needs work?If I didn't have the garage ac I can't imagine how terrible it would be. Yes, in Texas having two seems necessary, but seems wrong never the less.The air that comes out of the vent in the front master bedroom is barely a trickle, while in the back it's blowing like a storm.When I checked the temperature at the vent, it was putting out 55 degree temperature, so more than 20 degrees below the outdoor temperature.Thanks!Mark.

The ONLY way to verify the AC unit is running to spec, is a Temp corrected AMP draw of the compressor. That is what I would do if you were my customer. You look at the SPEC plate of the AC. On that spec plate will be the AMP draw of the compressor. That amp draw is based on 95 degree ambient temp. You run the AC for a minimum of 15 minutes and then take the amp draw with a digital clamp on meter of the compressor wire. For EACH 10 degrees above 95 ambient you add 1 amp to the draw. For EACH 10 degrees below 95 ambient you subtract 1 amp. So if your AC spec is 12.8 amps for the compressor and it is 85 degrees ambient the compressor amp draw should be about 11.8 amps. This just verifies the unit is running to spec. It does NOT give you clues if the AC system is not installed to spec with the baffles and ductwork sealed correctly. If the unit is running to spec, then you dig deeper to find if there is a problem with distribution of the cold air. You also need to verify the SIZE of each AC unit. They will be either 13.5k BTU, 15k BTU or HC. HC is a model that is slightly lower than 15k BTU but is almost 15k BTU. If you post the Model number and brand of each AC I can give you the BTU size. Doug

Pull the vents out and use your phone to photo the duct work and see if there is still a blockage.

Check for restriction in the ductwork and also drop the plenum cover and make sure that it is properly sealed to the duct system and not leaking into the attic.

I would check the air speed coming out of the vents for the rear AC and compare with the speed from the front AC unit. That will tell you if the fans are putting out similar volume of air. As long as the temp coming out of the vent is at least 20 degrees below the outside temp it sounds like it's in specs for cold air output.

When it comes to air flow I see some very "Strange" results on my Dual Ducted System. OFten I will get more air flow from selected vents or so it seems. with one or the other running. and less with both running. Or so it seems.Another thing.. Both my 15K jobs work well per testing but the front one is "less effective" Cause the FRONT is bigger. WAY bigger.

Underperforming front A/C? | Good Sam Community

dougrainer
Nomad
Jul 25, 2018
The "20" degree difference is just a way to determine if your unit is cooling without doing the correct check outs. The 20 degree is done by checking the COLD air at the closest duct outlet to the AC and the Intake filter. There is a margin of error of about 2 degrees either way. 85 in at filter, 65 at the closest Cold duct would indicate the ac is at spec. This does not tell you if the ducting and baffles are installed correctly or leaking air. Doug
novasbc
Explorer
Jul 25, 2018
I am going to inquire with my dealer what exactly they consider as up to spec, and do as you say. Thanks.

Bob Landry wrote:
the bear II wrote:
I would check the air speed coming out of the vents for the rear AC and compare with the speed from the front AC unit. That will tell you if the fans are putting out similar volume of air.

As long as the temp coming out of the vent is at least 20 degrees below the outside temp it sounds like it's in specs for cold air output.

The 20 degree difference that everyone likes to quote but is clueless about, is across the coil, not between inside and outside air. Outside ambient temperature has zero to do with determining operation of a unit except in using the measurements Doug stated earlier to determine if it is properly charged. After that you are looking for an installation problem, or the unit is simply undersized for the space it has to cool.

The OP needs to print out the instructions Doug gave and take them to the shop that said his unit was good and ask if they checked it using this method. If they did not, they need to start over because if they call Dometic looking for troubleshooting help, this is what Dometic is going to tell them to do.I'm betting most shops will look at you like you're nuts.
novasbc
Explorer
Jul 25, 2018
I am hoping this weekend to inspect things to see if any items like you describe are still wrong after their original repair.

I have a 15k unit up front (the underperforming unit) and 13.5k in the garage. I would thought with both of them it could keep the camper nice and cool without having to run all day :).

Bob Landry wrote:
the bear II wrote:
I would check the air speed coming out of the vents for the rear AC and compare with the speed from the front AC unit. That will tell you if the fans are putting out similar volume of air.

As long as the temp coming out of the vent is at least 20 degrees below the outside temp it sounds like it's in specs for cold air output.

The 20 degree difference that everyone likes to quote but is clueless about, is across the coil, not between inside and outside air. Outside ambient temperature has zero to do with determining operation of a unit except in using the measurements Doug stated earlier to determine if it is properly charged. After that you are looking for an installation problem, or the unit is simply undersized for the space it has to cool.

The OP needs to print out the instructions Doug gave and take them to the shop that said his unit was good and ask if they checked it using this method. If they did not, they need to start over because if they call Dometic looking for troubleshooting help, this is what Dometic is going to tell them to do.I'm betting most shops will look at you like you're nuts.
Bob_Landry
Explorer
Jul 24, 2018
the bear II wrote:
I would check the air speed coming out of the vents for the rear AC and compare with the speed from the front AC unit. That will tell you if the fans are putting out similar volume of air.

As long as the temp coming out of the vent is at least 20 degrees below the outside temp it sounds like it's in specs for cold air output.

The 20 degree difference that everyone likes to quote but is clueless about, is across the coil, not between inside and outside air. Outside ambient temperature has zero to do with determining operation of a unit except in using the measurements Doug stated earlier to determine if it is properly charged. After that you are looking for an installation problem, or the unit is simply undersized for the space it has to cool.

The OP needs to print out the instructions Doug gave and take them to the shop that said his unit was good and ask if they checked it using this method. If they did not, they need to start over because if they call Dometic looking for troubleshooting help, this is what Dometic is going to tell them to do.I'm betting most shops will look at you like you're nuts.
myredracer
Explorer II
Jul 24, 2018
We don't use our AC very often but sure did over the past few weeks in killer heat. The bedroom wasn't cooling down well and little air was coming out of the vent at the rear of the TT above the kitchen counter.

Took down all the vents. Found one where the ceiling was flopping down enough that the vent didn't push up into the duct by about 1/4" and air was being blown into the ceiling space. Got some 2-1/2" screws and pulled the ceiling up closer to the duct. I also found that the vents weren't sealing well against the duct so I used some self-adhesive foam tape (for doors & windows) around each vent where it pushed into the duct.

I also found that one duct wasn't sealed very well at the AC unit so used some aluminum foil duct tape to seal it properly. (Don't use regular "duct" tape or Gorilla tape as it's not meant for ducts.)

That all made a huge improvement and got the temp. down better and more evenly. However, the 13.5K AC unit just isn't anywhere enough in hot weather and I probably coulda died even when it was running okay. Should have got the optional 15K AC unit when we ordered our TT. :(
rjsurfer
Explorer
Jul 24, 2018
Another thing to check is the separation between the two sections of the A/C. By that I mean there is cold air blowing out from the coils and warm return air coming back in. They should be isolated from each other.

Pull the plastic frame down from the A/C and look inside you will see what I mean. The factory uses silver tape and pieces of foam material to keep them from cross contaminating. On my unit it was easy for a lot of the cold air to just move across and mix with the warm return air going back up into the coil.

Also there were places where cold air could leak into the "attic" or empty space in the roof.

My cold airflow almost doubled after spending an hour fixing the factories poor workmanship.

Another spot to check are the circular vents. Take them down and see if the silver tape is preventing cold air from leaking into roof space. And see if the ducts haven't collapsed or squeezed down between the vents.

Ron W.
novasbc
Explorer
Jul 24, 2018
I'll take a few pictures, still haven't had a chance to crack it open yet though.

I really need to though, even to keep it at 90 degrees inside it runs all day long. In Sunday, I left both units on, and got the day I nearly reached 90 kWh. Right now we're staying in it while renovating a house, but that much electricity add up. Doesn't help that it's been 108-109 here for the last week.
wopachop
Explorer
Jul 12, 2018
Im new to trailers but not new to construction. Can you take a picture of your front AC unit? Im curious if the only outlet is the ducts?

I would add extra outlets to your existing ducting.

Or more expensive option is install a different style AC unit. A unit that has more free flowing airflow. For example the unit in your garage.

I think trailer companies dont want to blast cold air straight down onto your bed. So front bedrooms get ac units like you have now.
novasbc
Explorer
Jul 12, 2018
Thanks for all the comments, for some reason I got no email notifications, I thought I set it up for instant email notifications, but I bet it went to spam.

I'll check my ducting myself to start with as some have said, it seems reasonable to stay with.

If that looks good, I'll start with the serial tests described here.

It seems like what I'm describing isn't normal, so I'll keep digging until I can root cause it.
doxiemom11
Explorer II
Jul 10, 2018
We had neighbors with only a front living room air, unit wired for a 2nd in bedroom. They constantly complained about just the 1 not cooling enough. Ordered a 2nd to be installed in bedroom after having it in to the rv place and check 2 or 3 times and always returned saying - working fine. Son installed 2nd A/C and decided to clean and check front one. Baffles in vent were closing off the vent most of the way and the cooled air was barely coming thru. He readjusted the baffles and guess what ---- 2nd A/C not even needed now .

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