Outside temperatures

[Chuck B 2004 Windsor]

I remember reading in a earlier life that the air conditioners cannot bring down the inside temperatures lower than 12 or so degrees lower than the outside temperatures.  

Chuck B 2004 Windsor

[Nevada Rob]

I was under the impression that an A/C unit in good operating condition should be able to exchange heat temps in the 22 -24 degree range. Humidity will play a roll in the overall big picture. Lower RH conditions will be better for an A/C unit. 

[Tom Wallis]

Not true. Modern automotive AC unites can create air temperatures in the 35 to 45 degree range at the duct. What the room temperature becomes depends on the capacity of the unit in volume and the insulation and size of the room. Consider your refrigerator and freezer. They work on the same principles as  your AC.

Edited June 10, 2021 by Tom Wallis

[Chuck B 2004 Windsor]

True, BUT the door stays closed 99% of the time.  Try leaving the door open and see what happens.  Chuck B 2004 Windsor

[Tom Wallis]

Yes, well if you leave the windows and doors in your motorhome open while your AC is on you probably won't even lower the temperature 12 degrees.

[Karl Hampton]

Our experience has been, two new AC units in a 40’ MH lowers temperatures 20-30* depending on humidity. Keep the AC on 24/7 or from early morning into the day, don’t try to cool from 95* down to 70*. Playing catch up is more difficult than maintaining the temp @ 75* or whatever temp you prefer. If you leave doors and/or windows open while running the AC 🤔🥴🤷‍♂️ Normal ingress & egress excepted. 1998 Signature

[Ray Davis]

When the grandkids are with us I think the fridge and coach door are both open about 90% of the time.   😬

Maybe they will get a coach before I die and I'll hold their doors open,  if they will let me go.   👨‍🦳👨🏻‍🦯

[Nevada Rob]

Chuck when I said 22-24 degree exchange temp I meant overall ambient interior air compared to outside. The temp at the air duct vent is a good indicator of how well your A/C units are operating but does not mean you can make the overall air space inside that temp. With that said everything in your coach is working against that cold air. The sun on the roof, heat through the windows and even body heat from people. As Karl stated, try to keep everything inside the coach cool to start with. I have opened my coach up here on hot days with it parked under the cover and the interior temp is 110 to 115 degrees. Everything inside is that temp. The cabinets, walls, floor, even the toilet all radiating heat. It takes a few hours of running all three A/C's to get it down to about 80 degrees. If you are only able to drop about 12 degrees as asked in your original post, then maybe a good A/C guy might be needed. 

[RustyTools]

Nevada Rob is right, it's the difference between the temperature going in the AC return vent (within the coach) and the temperature coming out the ductwork (and back into the coach), not necessarily the air that is outside of the coach.  The 'outside air' and humidity does play a part in general by making the overall AC unit work harder, but the rule-of-thumb is to look for a ~20-25 degree change inside.

[Frank McElroy]

Well it took me 10+ years using me coach in both hot and cold weather to discover why me AC didn't cool and Aquahot didn't heat as well as I expected.

First, in freezing weather I discovered all the huge and I mean huge leaks under the dash and the drivers side area below the arm rest.  Two cans or black spray foam sealant later and those air leaks were sealed.

Then I found huge air leaks under the front and rear PS side slides that I fixed with rubber swipers in the lower channel slide guide rails.  Solved the insect problem too.

Aquahot on electric could now heat the coach to 75 with outside temps down to 40 - before, the best I could do was 75 inside with outside temps down to 50.

Lastly, when removing the AC roof covers to clean the condenser coils, I noticed no dirt on the coils.  Hmmm, after 10 years, no dirt on the coils, that's not right.  I discovered that there were missing and incorrectly applied foam barriers applied to the roof AC covers.  This allowed air to bypass the cooling coils.

After fixing all these issues, wow, I can cool and heat the coach so much better.  95 outside - 72 inside and the 3 AC units are still cycling on and off maybe 50% (that is with the shades pulled on the windshield and windows).  Before the modifications, I was running 3 AC units at 100% on time and lucky to maintain 75 with outside temps at 95.

Our coaches are poorly insulated as would be expected with only 2" thick walls, but the biggest problem is air infiltration by poor dash and slide sealing along with poor use on foam sealant on the roof AC covers to direct air through the condenser coils.

Once I fixed these issues, wow - I sure now have a really happy wife!

[Ivylog]

Interesting that our 04 Dynasty (owned for 14 years) and our 08 Navigator (owned for 3 years) didn’t have those problems although I haven’t had the covers off the 3 ACs on the Navigator as they cool well. Agree the foam seals are critical for good operation. 
Frank, do you know when your 08 as built? Ours was 10/2007.

[Hypoxia]

When I acquired my Signature the house A/C didn't do much.  I looked at the service records which had a number of reports of A/C not cooling.  They even went so far as to install a new rear Heat Pump, which made no difference.  The "Professionals" spent a lot of the previous owners money but no joy.  I removed the rear closet ceiling vent and could see daylight.  I found the rear cap for the duct main trunk had never been installed by Monaco & the A/C was blowing outdoors.  I repaired that as well as taping the leaky joints and installing new foam on the rooftop units.  Next was taping the duct leaks where the rooftop units meet the main trunk, lots of airflow blowing out there.  I installed ceiling fans in the bedroom and living room and have been satisfied.

evaluating_ac_performance.pdf

Edited June 11, 2021 by Hypoxia

[Steven P]

Just to chime in about poor insulation.  I'm currently replacing my radio speakers and stuck my hand in the holes.  There's visible insulation,  but reaching further there is no insulation above the ceiling ductwork.  That's not helping...

[Frank McElroy]

My 08 was built in March 07.  I thought my roof AC was ok until I opened the roof AC units.  That's when I discovered the sealing foam was installed incorrectly.  Once I fixed it, wow, what a huge difference in performance.

[Steven P]

2 hours ago, Frank McElroy said:

My 08 was built in March 07.  I thought my roof AC was ok until I opened the roof AC units.  That's when I discovered the sealing foam was installed incorrectly.  Once I fixed it, wow, what a huge difference in performance.

How is the sealing foam supposed to look?  What did it look like before?   This is the first I've heard of this and am intrigued. Thanks, Steven 

[Frank McElroy]

There is a foam gasket that was to be attached to the top is the condensing coil to seal it to the top cover so that when the top cover is installed it creates an air seal.  That way all the outside air from the fan is pulled through the condensing coil.  What Monaco did on my coach was to attach this foam seal gasket to the top cover but because it was misaligned, maybe only half the air was flowing through the coil.  So, I removed the gasket from the top cover and attached it directly to the top of the condensing coil such that when the top cover was reinstalled, I got a good air seal.  My AC units are Dometic Penguin model 630515.331

[Ivylog]

The foam seal is about 1” square with sticky on one side. Like above you’re better off attacking it to the metal flange, not the plastic top.

[Frank McElroy]

Sometimes pictures are worth a thousand words.  Here is a picture of how Monaco at the factory installed the foam seal to the AC top.  The other picture shows how I correctly installed the seal to the condenser and associated other areas so that all the fan air now flows through the condenser coils.

I'm the original owner and after 10 years I was wondering why there wasn't much debris collecting on those coils.  Well, now I know why.  What I can say is that it made a huge difference in the AC cooling capacity after I properly installed those foam seals on my 3 rooftop AC units.

[Hypoxia]

Air flow is so important.  On a stick house A/C if the condenser fan stops, the compressor overheats in about 5 seconds and shuts down,  RV A/C units also are that dependent on air flow.  What Frank accomplished cannot be emphasized enough.

[Steven P]

I'm gonna have to go back up and take the covers off and see what I see.  I have 2 Dometic Duotherm heat pumps.  I'm guessing the foam should be similar? I have a 630035.331 and looking at the diagrams, I do not see a foam gasket.  Dometic_Penguin_AC-HP_Parts_List.pdf

Dometic_Penguin_AC-HP_Parts_List.pdf

Edited June 12, 2021 by Steven P

[Frank McElroy]

Yes, I also have the Penguin heat pump.  I believe part numbers 15 and 16 are the gaskets.  Somewhere I found a picture of how to properly install them but now I can't seem to find it.  It will be interesting to see what you find when you pull off the top cover.

[Steven P]

I have the below pic from the other day and I am not recalling a gasket anywhere.  Also, my covers were replaced 3 years ago due to a RV service company cracking the original ones.   I don't know what they looked like under the covers but I know there are no gaskets attached to the covers.  This pic is with installation of the Soft start. Any sources for the gaskets?  Thanks. 

Edited June 12, 2021 by Steven P

[Frank McElroy]

The foam tape might be installed on the top cover and if done right, you should get a good seal such that all the air flows through the condenser.  On mine it wasn't done correctly so I just put the foam directly on the condenser and associated parts vs trying to figure out how to get the foam properly positioned on the cover.  I looked up where I bought new foam tape and back in 2017, Dyers was selling the kit with 10 feet for $10.  It was item #83697.  I just checked and it is out of stock.  But there is nothing special about 1.5" x 1.5" foam tape.  I'm sure you can find a supplier on Amazon.

[Scotty Hutto]

Echoing what Frank said…. My gaskets were attached to the covers (and looked about like Frank’s), and when I replaced the covers after a storm blew them away in summer 2017 I attached the foam to the AC unit like Frank did. I wasn’t as smart as Frank… I just couldn’t figure out where the gaskets were supposed to go on the cover, but I could clearly see where they had been touching inside the unit, so…. As my older brother would say… “even a blind hog finds an acorn once in a while…”

[Paul J A]

3 hours ago, Steven P said:

I have the below pic from the other day and I am not recalling a gasket anywhere.  Also, my covers were replaced 3 years ago due to a RV service company cracking the original ones.   I don't know what they looked like under the covers but I know there are no gaskets attached to the covers.  This pic is with installation of the Soft start. Any sources for the gaskets?  Thanks. 

Have you looked on the Mfg. of your units web site for that information? Maybe a email to tech support asking for it? A drawing of the template they use for locating the tape during manufacturing?