Opinions on new air conditioner

[Fulltimer50]

Originally Posted by Laco

Correct the roof AC's are not at all efficient, compared to what is available for residential. There are limits, since they must run on 120 volts. If efficiency was to be increased meaningfully they would have to run on 220 volts, which is not available from any of the pedestals that I know of in any RV park I have been to.

If wired properly, every pedestal that provides 50 amp is 220v.

[DanChateau33SW]

Originally Posted by skag101

I have a 98 Windsport. It has two air conditioners but being a 30 amp rv i can only run one at a time. Pretty sure the ones I have are 13,500 BTU. We traveled to FL this spring and the air just didn't cool enough. We usually make two trips a year there.
Would it make enough difference to change to a 15,000BTU ? Cost for the unit is around $700-$800 for a ducted unit. Just wondering if it would make that much difference. What are your thoughts?

Short answer...YES it will make a huge difference! We had a 27'TT that we had a 15k BTU air conditioner installed, running 30A power. We were camping one time it was 107 outside and inside our trailer was around 68 degrees. All of the Class As that had 2-3 A/C units were struggling to maintain 80 degrees inside, including our friends with their 33' Class A.



that was in WA state. We now live in South FL and our newer 33' Class C has (2) 13,500BTU units. We haven't been in a situation yet where they can't keep up, but this will be our first summer camping with it. If they can't keep up, we will definitely be upgrading to 15k BTU units.

[Chance]

Originally Posted by Laco

Correct the roof AC's are not at all efficient, compared to what is available for residential. There are limits, since they must run on 120 volts. If efficiency was to be increased meaningfully they would have to run on 220 volts, which is not available from any of the pedestals that I know of in any RV park I have been to.

European RV standard is higher voltage around 220, and their A/C specs show them to be generally less efficient than ours.

Voltage has some impact on efficiency, but it’s minimal in the 11,000, 13,500 or 15,000 BTU/hour size range. It’s at higher cooling capacities that higher voltage is needed, like my 60,000 BTU/hr unit at home.

Newer RV air conditioners may not match residential, but they are much more energy efficient than units from 20 years ago. A Power Saver today can run on about 10 Amps when a similar size unit from decades ago pulled closer to 15 Amps. If that’s not more efficient, I don’t know what is.


By the way, I’m fairly certain that the reason RV A/Cs are less efficient than residential is because they are engineered to be light and more aerodynamic, which limits their size to smaller than ideal for thermal cooling efficiency. Heat exchangers are smaller, and thus less efficient.

[Chance]

Originally Posted by DanChateau33SW

Short answer...YES it will make a huge difference! We had a 27'TT that we had a 15k BTU air conditioner installed, running 30A power. We were camping one time it was 107 outside and inside our trailer was around 68 degrees. All of the Class As that had 2-3 A/C units were struggling to maintain 80 degrees inside, including our friends with their 33' Class A.



that was in WA state. We now live in South FL and our newer 33' Class C has (2) 13,500BTU units. We haven't been in a situation yet where they can't keep up, but this will be our first summer camping with it. If they can't keep up, we will definitely be upgrading to 15k BTU units.

It doesn’t work that way. Rated capacity is a very close estimate of cooling capacity under controlled conditions, so a 13,500 is very close to 90% of a 15,000 — no big difference beyond that.

Two 13,500 will deliver 27,000, which beats 15,000 every day of the week under similar conditions.

I don’t doubt your observations were valid for other reasons, but it wasn’t because there is some magical capacity bonus associated with 15,000 units. Most likely your trailer didn’t have a huge windshield, maybe had smaller windows, and maybe better insulation in general.

[SuperD]

Originally Posted by Chance

In air conditioning, moving more air doesn’t always help because cooling capacity is limited for the most part by compressor and heat exchangers capacity. Blowing more air across the evaporator will mostly feel good if you’re standing near the vent so it blows on you (like the effect of a fan), but it won’t increase the thermal cooling capacity of an A/C appreciably. The right amount of air is needed to reduce humidity.


The problem here is that we’re missing NEEDED information to diagnose what’s really happening.

Why does a large motorhome have 2 A/Cs if they can only run one? That’s rare.

Just my 2 cents ....

The ducts in most Thor’s are narrow and very restrictive, sometimes even blocked by poor construction, adding the vent allows less restricted air movement and a better ability to direct the air. Even with the vent in place you are not exceeding air movement above what the system can process efficiently.

This individual has only one AC on their coach, I offered this option as an alternative to adding a second AC and the problems associated with adding additional wiring.

Thor offers many coaches with the option of dual AC, larger generator, and 50 amp wiring, they sell many with only a single AC to sell at a lower price point. As you may well know, Thor doesn’t give a rat’s ass if the customer is happy after the sale.

I have dual ACs on my coach, used to live in Texas where 105 degrees with 90+ percent humidity is normal. After installing the vent I ran only one AC many times unless I parked in full sun. Many other members have made this same mod with good results.

I would certainly gamble $20 to see if it works before I spent over $1,000 to install a second AC!

[Chance]

Originally Posted by SuperD

The ducts in most Thor’s are narrow and very restrictive, sometimes even blocked by poor construction, adding the vent allows less restricted air movement and a better ability to direct the air. Even with the vent in place you are not exceeding air movement above what the system can process efficiently.

This individual has only one AC on their coach, I offered this option as an alternative to adding a second AC and the problems associated with adding additional wiring.

Thor offers many coaches with the option of dual AC, larger generator, and 50 amp wiring, they sell many with only a single AC to sell at a lower price point. As you may well know, Thor doesn’t give a rat’s ass if the customer is happy after the sale.

I have dual ACs on my coach, used to live in Texas where 105 degrees with 90+ percent humidity is normal. After installing the vent I ran only one AC many times unless I parked in full sun. Many other members have made this same mod with good results.

I would certainly gamble $20 to see if it works before I spent over $1,000 to install a second AC!

SuperD, please go back and read the first thread post again, and you’ll see that he already has 2 A/Cs, and that his biggest problem is not being able to run both at same time.

If he’s not needing to cool by running A/Cs from a 4-KW generator, and only cools when on shore power, then his best choice is probably a 50-Amp upgrade which should cost less than a new A/C. Or even cheaper is to run one A/C directly from pedestal 20-Amp breaker, leaving rest of coach on 30-Amp service.

But if he will be boondocking off a 4-kW generator, that’s a different story. There’s a lot of missing information. We don’t even know if he’s got a small motorhome without slides or a huge one with 2 or 3 slides. The first may get by with minor tweaks, the second would need 2 A/Cs running at same time no matter what.

I’m just guessing because there’s a lot of information that’s missing.

[Bob Denman]

Is it just me; or is anyone else in here curious why a Motorhome would be built and equipped in such a way, that you couldn't run both air conditioning units at the same time?

What am I missing?

[Chance]

I mentioned that already. Most “LIKELY” any 30-Amp motorhome from that age had one A/C from factory, and the second one was probably added in bedroom area afterwards. Most likely it also has a 4 kW generator.

That it can only run one unit at a time is odd because if the original A/C could cool living room during day, then at night it should have been able to cool the entire coach.

I’d guess they wanted to make bedroom super cold at night, or else had a way to power the second A/C independent of 30-Amp service. It’s possible present owner isn’t the original owner, and may not be aware of what was done. Lots of unknowns IMO.



P.S. — Or owner took naps in bedroom during the day. Who knows?

[Bob Denman]

So this is probably a self-inflicted wound...
I was assuming that the rig was delivered in this configuration; Thanks!

[revjeffrey]

Take the cover off on inside, run the air. MASSIVE air flow and quick cool unit. Put back on seems very restrictive. My point is.... After being on this forum do I trust Thor engineering for ducting AC? After being parked in Circus Circus Vegas 3 days 118 degrees heat. My answer was No. $8.00 VENT 20min time, looks Factory. Cool unit 1 air...

[Beau388]

Originally Posted by gmtech16450yz

Why does everyone think the "newer" a/c's are more efficient? They haven't changed the design in like 30 or 40 years!

If you need better efficiency while driving, you can most definitely improve on the efficiency or amp draw of any RV roof air. Not a whole lot you can do when parked.

Lets not go overboard. The Colman Mach first produced in 1969 was rated at 10,000 btu and drew 15.8 amps @ 80 degrees ambient. That is an EER of 5.5 The current Mach 1 PS is rated at 11,000 btu and draws 9.6 amps @ 80 degrees. That is an EER of 10.0. That is a considerable increase in efficiency in my book.

[gmtech16450yz]

What you guys are talking about with regards to airflow and restriction is absolutely a factor that can be "tweaked".

There is a happy medium or sweet spot when it comes to the amount of air going through the system. There are also different airflow approaches to cooling the insides of RV's or houses for that matter. On both sides of the "perfect" efficiency, you can lean more towards increasing airflow or more towards keeping the outlet temps colder (or warmer in a combined system like a house).

Think about this... the air in your RV is 100 degrees. You want it down to 70. To take what I'm saying to extremes, you can either replace all of the air quickly with cooling air that's just a little bit colder, or slowly replace all of the air with cooling air that's way colder. Again taken to extremes, the perfect air conditioner would be one that could replace 100% of the 100* air in the RV with 70* air instantly. We don't have that. lol. Another way of looking at the airflow thing is in any one minute, you can either drop 100% of the entire air in the RV 1 degree, or drop 10% of the entire air in the RV 10 degrees. (Numbers not to scale. duh.) That's the airflow side of the efficiency.

The A/C can only remove X amount of heat from X amount of air. That's the 13k or 15k part. What does have an effect on that is the airflow. If the airflow isn't ideal, high or low, you're not going to be at peak efficiency. I would imagine that what you guys are finding is true, that opening up the airflow does help because even though the outlet temps are a little lower, you're replacing more of the air faster. I personally like leaning towards more airflow with less temp change than less airflow with more temp change. That's how I have our house HVAC setup, TONS of airflow to move more air, even though it's at less of a temp change. The downside and compromise in all of this is noise. Most people want their home HVAC's to be silent. That means less airflow. So you have no choice but to make sure that reduced airflow has a huge temperature change.

I learned a ton about the RV A/C side of all of this many decades ago when I was trying to get a roof air and generator system working in our little 19' Tioga class c. There was no room for a full generator so I built in a tiny little Yamaha 600 watt portable into the original propane bottle storage cabinet. I figured out how to run a Coleman roof A/C off of that little generator, even when driving down the road! I learned just a tad about how to make RV roof A/C's efficient to accomplish that. lol. We used that setup successfully for about half of the 100k+ miles we put on that little Tioga, still worked great when we sold the RV.

Anyway... has anyone else noticed that although we're all learning new things about air conditioners, the OP hasn't said another word since his first post? hahaha.

[gmtech16450yz]

Originally Posted by Beau388

Lets not go overboard. The Colman Mach first produced in 1969 was rated at 10,000 btu and drew 15.8 amps @ 80 degrees ambient. That is an EER of 5.5 The current Mach 1 PS is rated at 11,000 btu and draws 9.6 amps @ 80 degrees. That is an EER of 10.0. That is a considerable increase in efficiency in my book.

That's for the PS. I don't think most of the RV's are running around with the PS models are they? (I honestly don't know.) The standard 15k like is on my '18 Vegas draws 15.3 amps. The 13.5k's draw the exact same 15.3 amps. The 13.5k PS draws 11.2, which I admit is a nice improvement, but if you take the PS's out of the picture, RV roof A/C's haven't changed much since at least the early '70's.

[Bob Denman]

Originally Posted by gmtech16450yz

Anyway... has anyone else noticed that although we're all learning new things about air conditioners, the OP hasn't said another word since his first post? hahaha.

He's busy taking notes...

[gmtech16450yz]

Originally Posted by Bob Denman

He's busy taking notes...

Hahaha.

That's what's cool about the internet. The person asking the question isn't the only one that can benefit from the answers.

I'm still wondering if he's talking about being parked or driving. I can absolutely help him make his A/C more efficient and cool better when driving. Talking about amperage, I dropped the amperage of our Coleman Mach 8 significantly when driving. The amperage draw of these roof A/C's actually goes up quite a bit when driving. Mine DROPPED amperage draw when driving after I was done with it. If I remember right, parked was 9-10 amps, driving was 11-12 amps stock. I ended up with something like 8-9 amps parked and 7-8 amps driving! We literally tried to keep moving when it was really hot out so the generator wouldn't trip the circuit breaker.

[Chance]

Originally Posted by Beau388

Lets not go overboard. The Colman Mach first produced in 1969 was rated at 10,000 btu and drew 15.8 amps @ 80 degrees ambient. That is an EER of 5.5 The current Mach 1 PS is rated at 11,000 btu and draws 9.6 amps @ 80 degrees. That is an EER of 10.0. That is a considerable increase in efficiency in my book.

Are you sure you want to risk confusing people with facts?

[Bob Denman]

I found a picture that shows a worthwhile modification that can be made to the AC cover: adding an additional vent!

http://www.thorforums.com/forums/att...1&d=1528823080

[gmtech16450yz]

Originally Posted by Chance

Are you sure you want to risk confusing people with facts?

Oh like this maybe?

Lol.

1983 Coleman Mach III EL 13.5k... 16.0 amps. (Original old style axial non-rotary compressor.)

1983 Coleman Mach 3 13.5k... 13.8 amps. (Rotary compressor, same as current models. I think the rotary's came out in the late '70's?)

2018 Coleman Mach 3 Plus 13.5k... 15.3 amps.

2018 Coleman Mach 3 PS 13.5k... 11.2 amps.


So yeah, they've lowered amp draw from 16.0 to 15.3 over the last 4 decades on the by far most common units. Yeah for them. And yes, if you take the worst, oldest design vs. the best newest design, the difference is 16.0 to 11.2. That's not bad obviously. But that's 1969 vs. 20xx. Over the last 3 decades though, they've actually gone UP from 13.8 amps to 15.3 amps on the most common units on the road. According to this Coleman document from 1983, the Mach 3 Rotary was MORE EFFICIENT than the current Mach 3 Plus that is on most RV's today.

My point was that the basic design, thus the basic efficiency of the rooftop RV air conditioner hasn't changed in about 4 decades. Joe Average RV buyer 30 years ago would have driven out of the dealership with a roof air (13.5k) that had an amp draw of about 12-15 amps. Joe Average RV buyer today would drive out with a roof air (also 13.5k) that also draws around 12-15 amps. Fact.

[Chance]

I still don’t see an 11.2 Amp 13.5 A/C unit in 1983. You’re confirming our point.

[Bob Denman]

If nothing else: at least they're making them lighter, cheaper, and less durable...