2 Air Conditioners on 30-Amp Service

[Chance]

Upgrading air conditioning capacity when an RV only has one 15,000 BTU/hr A/C usually means adding a second A/C unit, but more often than not RVs that have only one A/C from factory come with a 30-Amp service, and if it's a Class A or Class C motorhome with a generator it will likely be an Onan 4,000-Watt size.

We know that upgrading electrical to 50-Amp service is one option that works, as is upgrading to a 5,500-watt generator. These upgrades essentially allow air conditioning capacity to be doubled by adding a second A/C. This is expensive, and may be unnecessary since too much A/C capacity isn't necessarily a good thing anyway.

The other often-reported approach that is inexpensive and works well is to add a second A/C and run it separately from the campground's 20-Amp circuit at the pedestal. The main limitation with this approach is that the 4-kW generator may not run two standard A/Cs if tailgating or boon-docking (i.e. -- without shore power).

Often it is said that you can't run two A/Cs with a 30-Amp service, but that assumes you have two large and inefficient air conditioners. There is no doubt whatsoever that a 30-Amp service can't run two 13,500 or 15,000 BTU/hr air conditioners like the cheaper units often supplied by manufacturers. Simple math confirms that.

However, all A/Cs are not the same -- in capacity or power requirements.

When we looked at a used 30-foot Class A with one A/C a year or so ago, I also looked at options to upgrade air conditioning that could still run from 4-kW Onan so we could tailgate in summer, and determined (from specifications) that I should be able to increase A/C capacity by approximately 50% by going to two new high-efficiency 11,000 BTU/hr Power Saver A/Cs. Further research on RV forums revealed various owners have successfully run up to a 13,500 and an 11,000 BTU/hr high-efficiency A/C on a 30-Amp service.

The numbers show it should be possible, and it's already been done to confirm it will work under the right conditions, but it creates compromises that may be difficult to accept depending on how RV is used.

Please brainstorm away, both Pro and Con.

[wredman]

how many amps are all of these air conditioners drawing?

[MiramarVA]

While using 2 A/C high efficiency units on a 30 amp service may be possible, using any other electrical appliance, outlet, etc. may not be practical. If you have to keep turning off one of the units in order to make a meal or whatever, is it really worth it?

[gmc]

While I believe you could run 2 high efficiency AC's on 30A service - I agree you wouldn't be able to do much else without tripping the main... (microwave, coffee pot, blowdryer - even one of these will push you over.)

If ordering a new rig - the 50A upgrade is the way to go in my opinion... More than 3 times the available power for anything you want to do. And even outside of FL, TX, AZ in summer - even if you just need one - you always have a spare on board (I alternate between them when only needing one - usually running the one furthest from where we are sitting (using the ducts to spread air throughout) to reduce noise levels.)

In a current rig - bringing an extra 20A line in would be my preference to avoid the issue above. As you mentioned though - doesn't help with boondocking... Perhaps a switch to select the source for the 2nd AC - run it on the 30A when you have to (assuming high efficiency) - switch to the extra 20A when you can.

[Beau388]

I lived with a single Coleman Mach 3 power saver in my previous class A motorhome. Typically amperage draw is 12 amps. In very hot temps, 110 degrees (concrete pad, no trees in Tulsa, OK in July) and I never saw more than 13 amp draw. If you are traveling down the road you would probably not have anything running but the A/Cs. If you were worried about the converter drawing power, you could throw the circuit breaker and depend on the engine alternator to keep the batteries up.

[JamieGeek]

If you were boondocking perhaps you'd want something powered off of 12V?
TRUCK SERIES — Cruise N Comfort

Another one: http://www.arcticbreeze-truckac.com/

They are kind of pricey, but so is adding a 2nd A/C. Also granted these are designed to keep the cabs of trucks cool--a bit smaller area than a 30+ft class A.

[Chance]

Originally Posted by wredman

how many amps are all of these air conditioners drawing?

A standard "modern" 15,000 BTU/hr A/C can be rated at 16 Amps under normal conditions. Desert conditions requires more power. Old A/C units can be even worse.

A new 11,000 BTU/hr high-efficiency A/C is rated at just under 10 Amps. Under normal conditions (80F inside and 95F outside) two of these should pull about 19 Amps.

The new high-efficiency 13,500 BTU/hr is more efficient but because of higher capacity draws less than 11 Amps under normal rating conditions.


The point is that these can't be compared to old A/Cs directly, just like we shouldn't compare LED lights to older technology, or new TVs to old tube type. The difference isn't as great, but it's significant.

[Chance]

Originally Posted by gmc

While I believe you could run 2 high efficiency AC's on 30A service - I agree you wouldn't be able to do much else without tripping the main... (microwave, coffee pot, blowdryer - even one of these will push you over.)

.....cut......

That is probably the biggest compromise I see; although it too has pros and cons.

On my "older" Class C we typically turned off the A/C while we ran the microwave for a few minutes off the generator. The 4,000-watt Onan just struggled too much with older lower-efficiency units. On rented Class Cs we often do the same.

I agree that if you were running two A/Cs with a combined load of 19 to 21 Amps, it would be necessary to turn one of them off for a few minutes to run a microwave, coffee maker, or hair dryer, but on the bright side one of the two smaller more efficient A/C could remain operational, which beats no A/C at all.

[wredman]

have the mini split systems been considered for RV applications.

[Chance]

Originally Posted by wredman

have the mini split systems been considered for RV applications.

I believe it comes down to initial cost, which is why RVs are relatively inefficient. There are small split systems for semi trucks, and basement A/Cs for luxury buses, but I haven't seen either on "regular" motorhomes.

Mini split units are much more efficient than RV A/Cs, but as I recall they cost a lot more. For their capacity (I helped a friend install a 12,000 BTU/hr unit) they are much larger and heavier than RV A/Cs. They gain higher efficiency partly by using larger heat exchangers (evaporator and condenser). Some use inverter technology (to vary speed and hence capacity) which makes them even more efficient.


What's interesting to me is that these new high-efficiency roof-mounted RV A/Cs still appear much less efficient than residential air conditioners. If you divide capacity by watts used, they are barely over an Energy Efficiency Ratio of 10 (although I'm not sure if they use same rating system). Residential A/Cs are easily in the 16 range, with a few exceeding 20. There is still room for improvement, although for RVs a major problem is that making them more efficient may also make them larger which adds to wind drag and height clearance.

[Beau388]

It seems you are confusing SEER (seasonal) with EER energy efficiency. SEERs are usually around 14 for the small units (1.5-2.0 tons) but the EERs are about 11. The 1.5 ton split units weight about 160 lbs. Roof top RV units weight 86-90 lbs and have an EER of 8.8 to 11. The 4 ton split units weigh 430 lbs and require 30 amps at 240 volts and have a SEER of 18 and an EER of 11.

[Chance]

Originally Posted by Beau388

It seems you are confusing SEER (seasonal) with EER energy efficiency. SEERs are usually around 14 for the small units (1.5-2.0 tons) but the EERs are about 11. The 1.5 ton split units weight about 160 lbs. Roof top RV units weight 86-90 lbs and have an EER of 8.8 to 11. The 4 ton split units weigh 430 lbs and require 30 amps at 240 volts and have a SEER of 18 and an EER of 11.

Im not sure why you think I'm confused. An EER of 11 is horrendous for a residential unit. My home A/C which is almost 15 years old is between 14 and 16. New A/Cs I've looked at for future replacement are much higher; although the cost goes up significantly as they are made more efficient. Deciding where to draw the line on cost versus benefit is tough.


Getting back to RVs, as mentioned by others above, if you are buying new, I would highly recommend going with a 50-Amp service on larger motorhomes and trailers. But the question that was brought up that led to this thread is what can be done with an existing RV that has a 30-Amp and or 4,000-Watt generator if the 15,000 BTU/hr A/C isn't quite enough capacity.

[Chance]

Well, it appears this exact question has been addressed and answered for us already. While looking at Jayco motorhomes, I noticed that all Alante floorplans except for the very shortest 26-footer come with 2 X 11,000 BTU/hr air conditioners, while specs also show 30-Amp service and 4,000-Watt generator. The shortest which has open floorpan comes with single 15,000 BTU/hr A/C.

So for motorhomes in the 26+ to 32-foot range, it appears a good compromise may be 22,000 total BTUs/hr, and the 2 A/Cs can apperently run on 30-Amp service and 4,000-Watt generator.

An additional question is whether this setup could work effectively without an EMS (provided by Jayco), or if it would become a pain to manage loads manually.

Also the question of cost to upgrade for those who own an existing RV with 30-Amps and 4,000-Watt generator. Upgrading to 50-Amps may not be too expensive, but upgrading to new 5,500-Watt generator may get costly.

https://www.jayco.com/products/class...s-and-options/