Why do RV air conditioners draw so much more power than window units?

[Firstime RVer]

Last year the rooftop AC unit went on the fritz just before a trip.
I rigged a standard 8,500 btu household window unit up since the trip was at the end of july.. I noticed that the rooftop AC drew 14 amps while cooling, while the window unit only drew 5 amps (only 2 amps when just the fan was running).
The rooftop unit is 13,500 btu, while the window unit is 8,500 btu. I would have expected the rooftop unit to draw about 8 amps based on the ratio of the cooling capacity of the units..
versus the 14 continuous amps. The window unit chilled our TT very effectively at a much lower power draw.. It also means I can travel with only one 2000 watt generator during the hot months when off the grid... Does anyone know if there are more efficient RV AC units available?

[Kuhl951]

Are you sure about that 5A draw on the window AC and how did you measure it? My 8500 btu window style AC on our trailer draws about 8.4A at full cooling/high fan, startup is of course higher but very brief. I know my Honda 2000W generator can't handle the startup loads on mine. I also have an 8800btu LG portable AC that draws 9.2A at full running load. Many of the newer AC units have very efficient scroll compressors but still 5A just sounds way too low.

[Firstime RVer]

Thanks for your reply.. I have a progressive industries EMS system which displays, voltage, frequency and amperage... I ran both AC systems individually today and noted the current while they were in operation.. It was 87 degrees here in NJ and When on fan only the rv AC drew 3 amps and the window unit 2 amps.. My champion 1700/2000 watt generator ran the 8500 btu GE window unit without a hiccup. What can I say?? I ran the RV AC unit for a little over 5 minutes, same for the window unit both on shore power.. Next I started my champion 1700/2000 watt inverter generator and ran the window unit for almost 10 minutes. I even got it to cycle between cooling mode and fan mode by adjusting the temperature setting..
Go Figure??

[Kuhl951]

Thanks. I'm sure your EMS system is much more accurate than my Fluke clamp-on ammeter. I've been suspect for awhile that my Honda has an issue in eco-mode, it doesn't seem to kick up RPM fast enough for AC capacitor starts. It will start the AC just fine in non-eco mode though and maintain AC operation in eco easily once running. The LG portable is actually a 9K BTU and I have no issue with it starting with the Honda so I assume it all about compressor efficiency at start-up. Our wall AC unit keeps us comfy on days up to about 105 deg. As long as the AC runs the wife is happy.

[Firstime RVer]

LOL keeping my wife happy with the AC is what started me on this quest...
We were talking about boondocking for a couple of days and the question of running the AC came up.. I need both of my champion 2000 Watt generators running in parallel to operate my rooftop AC unit.. and only one to run the window unit. (My generator's Eco mode wont handle the inrush of the compressor startup either) Here I was, trying to figure out how much gas I would need for a 4 day boondock and checked the current draw..
Now I find myself trying to figure out if I should bring extra gas with two generators or Just one generator, half as much gas and a window unit!!


Do you travel with your wall-mounted AC installed?? With my window unit rigged to fit into one of the TT windows, I was afraid to travel with it mounted in the window because I was concerned about the ability of the wall to handle the stress the AC unit put on the wall. So I just put it in the back of the pickup and Pop it in place after we arrive at the site.

[Firstime RVer]

By the way, Thanks for the info. I didn't know about the more efficient scroll compressors in the newer units. That may very well be the answer, since I only bought the window unit in August last year. Buying the AC unit was less expensive than cancelling the campsite reservations we had made!!

[Kuhl951]

Our tiny 15' Coleman is fixed and came with the factory AC so it's mounted internally in an extension of the OH cabinets. We keep getting smaller trailers over the years so the next phase will probably be a Prius with an ice maker for cooling We boondock quite a bit and are getting closer to getting it set up comfortably for the 2 of us and 3 dogs. We now like the travel concept of fast and light since we move frequently on many of our trips. When AC is cheaper than cancelling a reservation you are on the right track. I actually paid $15 for this LG 9K BTU portable AC I plan to use in my shop at a garage sale this morning, it works great and puts out 42* air on an 85* day!

[Firstime RVer]

When our rooftop AC went on the fritz, I actually bought one of those portable ac units.. It didn't work. (in hindsight it was probable defective) so I returned it and bought the window unit.. As shown in the pics, I fitted the plywood frame to the window and air conditioner and fastened a board with a grooved edge, to catch the top of the window frame, to the top of the plywood frame. Now the AC unit just pops in.. Ooooooh the adventures of RVing...