Got a Cool Cat? Check that Leaky Plenum

manyman297

While attempting to diagnose reasons our AC might not be performing at its peak performance (see this thread: https://tab-rv.vanillacommunity.com/discussion/14073/cool-cat-cooling-performance#latest) I went to check out the exterior vent and noticed the wall to the left of it was quite cool. Immediately I knew there must be leak in the ductwork connected to the Cool Cat unit. 

Diagnosing it was easy. Just stuck my arm into the AC filter under the dinette seat. I could immediately feel a draft almost equal to an entire ducted vent pouring out the side of the unit. 

After removing the bottom of the driver’s side dinette I saw the problem was simply that the coroplast plenum‘s corner tab had come undone due to the tape no longer holding. I restore it with some VHB tape and covered the tab with some gorilla tape for good measure. Draft completely gone.

I also used some foil tape under the ducts where they meet the plenum as I could feel some slight air leakage in that space too. 

This may not completely solve our cooling issues but I’ve essentially plugged a 4th duct worth of leaks. 

Side note: I figure out where the black tank sensors are too (pic below).

This is the forward side of the AC unit (right if you’re facing it inside). You can see where the tab has come undone (left side of photo with the white foam) and how I’ve used some VHB tape (added another strip after this photo) to keep that tab closed. 

Added some gorilla tape as well. Considered just gluing the plenum back into place but you never know when you might need to disassemble something down the road.

Front of the unit. The space under these ducts had some leaks as well. I used foil tape along the bottom where these ducts met the plenum.

Just to the left of the ducts you’ll see the black tank sensors.

qhumberd

Thanks for the post and the pictures. I just cleaned the filter in my  2019 400 (which in my case means unscrewing the panel on the driver side seat at the dinette) and found my unit identical to yours. I noted no leak spots in my unit, but there are lots of ways for things to vibrate loose so it is good to know where to check for air leaks.

manyman297

Wow, I didn't realize the older units required removing that entire seat bottom to clean the filter. It's kind of funny having that filter because the AC unit can still suck in air from around the unit (which wasn't that clean...fair bit of construction dust back there) and from outside somewhat. 

I actually found one of the glycol metal tubes leading to the overflow reservoir had come undone from a tie-down so I'm glad I opened up that compartment to secure it. Not a good thing to have hot glycol in pipes that are swaying back and forth during travel.

qhumberd

Actually I got my 2019 from the original owner and it was gently used but when I first checked the Coolcat compartment I was impressed at the lack of dust and construction bits in the compartment, which seemed pretty tight. Sorry to hear that the production line of late is apparently not as meticulous. Perhaps the pressure of being so far behind in orders and labor issues with the pandemic. But all my interactions with NuCamp have been positive and convinced me they do care about the customer. And being any trailer owner is just a lot of tinkering. No one cares about getting it right as much as we do, which is why this forum is so valuable. I hope when your compartment is sealed you will get better cooling performance.

manyman297

Thanks @qhumberd

It wasn't filthy...not as much of a cluster as our tent trailer was. There were hole saw remnants left in compartments, wire sheathing everywhere...just a mess. Just some heavy dust and some debris in the 400's AC compartment. 

Did a quick test today. It's about 90 degrees out..a little warmer than my test yesterday and more direct sun hitting the trailer. Closed the rear shade where the sun hits the most. Let the AC run for an hour and a half. It was noticeably cooler than my test yesterday. Overall it lowered the internal temp 13 degrees or so. Definitely comfortable to be in the trailer at that point. I can definitely feel more air being forced from the vents too. 

Regarding NuCamp's CS, this is where they shine above any other manufacturer I've dealt with. Warranty has been great so far. They don't question things and have even offered to compensate me for my time I've spent fixing a lot of these issues we've run across. I don't think that's their norm but considering the checklist of issues we've had I think they felt they had to (and our dealer is 3 hours away). 

Sharon_is_SAM

@manyman297 - I reviewed another thread in which a member thoroughly documented cooling a 400.  The conclusion was to anticipate the heat and start the A/C early.  It is true that once our TaBs become heat saturated, they take a bit to cool down.  @jimcenname added window film to reduce glare, UV and heat.  You can also try using some Reflectix (inside vs outside) and/or window awnings.  Circulating the cooler air with a fan also helps.  

manyman297

Thanks @Sharon_is_SAM. I also noticed today that venting the bathroom using the exhaust fan helped reduce the bathroom temps. Otherwise I think it becomes a heat box within the trailer and it fights the cooling of the AC.

I think anticipating the heat and cold is key for these systems.

Sharon_is_SAM

Yes - make use of the Fantastic fan too to get rid of the hot air.  Just like venting a hot car by rolling down the windows.

atlasb

If you haven't done it yet, adding a pair of vent diverters common to forced air floor vents helps separate the exhaust air from incoming air.  This helps also a shade or awning for the rear is good also to help control the heat.

manyman297

Thanks. I saw a post about making a diverter and might give it a try. Pretty easy to make it looks like.

Did another test today in nearly 100 degree weather. It took the AC about 2 hours to lower the temp about 22 degrees. Ultimately the thermostat read 77 but it felt like maybe 74 which was fine. The only downside is that the compressor pretty much just stayed on as it could never get the camper down any lower than that. Maybe that’s expected with those outside temps?

qhumberd

That sounds about right. Be glad you are not working with the 2020 400 AC unit. It is apparently smaller and can’t keep up in those temps and humidity. I’ll take 77 when it’s 100 outside any day when the AC for our tent camping friends only works by sweat evaporation. 

rhyno

I made a diverter as well and it works great. It's made from Coroplast, scored on one side to fold, affixed with outdoor velcro made to stick to stone/brick, then painted with high-temp grill paint that just happens to match our sidewall color.

The inner temp is usually 150-160 vs 170+ without. You can make a template from cardboard to find out if it works.

manyman297

@qhumberd Yeah, I guess I can't complain. Honestly, in the real world I don't see us being in 100 degree heat that often but I'm sure it'll happen at some point. Much better than no AC.

@rhyno Yes, that's exactly what I think I'll make. What performance gains did you see with that mod?

rhyno

@manyman297 - My AC was overheating once the exhaust temp hit the upper 170s especially when we were parked where that side of the camper faced south. It would then shut down the compressor until it cooled off. The result was the AC couldn't keep up and the indoor temp continued to climb. With the diverter in place the AC makes the inside downright chilly even in full sun. We've camped into the upper 90s with no issues.

I inserted a meat thermometer in the outside grill and used an infrared thermometer to measure the temps. The sides are usually below 120 even in during the hottest part of the day.

manyman297

Awesome! So in 95+ heat would the camper ever get up to temp where the compressor would shut off or would it just keep running? I notice that the AC will get the camper up to temp up to maybe 85-90 degrees. Anything above that the compressor just stays on constantly.

rhyno

YMMV based on location, sun exposure, humidity, etc but in my experience we can keep the camper at an avg of 74 degrees when the outside temp hits the upper 90s. The cool cat will cycle pretty frequently, run for a few mins then shut back off for about 10 minutes. I found that running the hvac fan on Auto keeps the humidity under control. If we run the hvac fan constantly, the humidity hits about 65% and stays there so instead we use a small fan to circulate the air in the camper.
Here's what a 5 day trip looked like for temp/humidity.