Yesterday was the first day the weather gotten hot enough to do some testing in the later part of the day when the van has been heat soaked in the sun. To my disappointment in no time the generator's overload protection was tripped. My heart sunk to say the least. I was running ethanol mixed premium fuel (not that premium octane has any benefit). I tried a number of time restarting and monitoring it still running in Eco mode, each time upon restart the engine will stumble and slow way down to which point the AC voltage dropped way low. What happen? I scratched my head dumbfound.
I then switched off Eco mode to see what it would do. Even more shocking is the generator could not sustain the AC upon the compressor restarting. I was very shocked that the engine RPM drop nearly the same as in Eco mode. Fortunately that is a big clue what the problem is. Short cycling. The time between the thermostat switched off and later switched back on was too short - around 25 seconds. I knew with short cycling the compressor head pressure does not have enough time to dissipate. When the thermostat calls for cooling again no amount of soft starting can reduce the starting current and actually spans to the running current due to this excessive head pressure on the high side of the system.
What to do, I pondered as the cycling is set by the designed in hysteresis of the Westfalia thermostat. I would hate to having to research and procure a more suitable thermostat. I immediately was wondering how is the design of the Coleman control. Does it have bigger hysteresis? I will never know.
As I gave the matter more thoughts, I reasoned that there are many factors that affect the minimum short cycling time: blower CFM, placement of the capillary tube, thermal conductivity of the tube, ambient air and the list is longer than I care to exhaustively enumerate. The fact is I have everything working against me, and the two biggest are the 1,800 ft elevation and ethanol mixed fuel. If I can get the generator to reliably power the AC I am in pretty good shape, but the question is how.
Since it had trouble even not in Eco mode the starting current beyond the soft start period clearly is way too high. So high the generator running at engine full capacity could not sustain to overcome the initial high head pressure. The solution is to fix the short cycling.
I reached up to begin pulling out the insertion depth of the capillary tube. I could not recall how far I had it inserted as it was so long ago. I did plan to tune it if necessary. I pulled most of it out leaving only a very short segment exposed in the outlet air stream. Sure enough that increased the minimum off cycle time of the AC significantly. with less of the tube exposed to the cooling airstream it take longer for the capillary tube to cold down and triggers the thermostat. The off cycles was now closer to one minute, and the compressor now can restart even in Eco mode, without substantial drop in AC voltage during surge current phase.
There are so many variables that affect how a relatively marginal generator can support this RV AC. For two nearly identical installation and similar generators we can have diversely different performances and experiences.
Today the weather is even hotter and sunny. I performed more tests and so far all is well. It took over one hour with the AC running non-stop to remove the heat soaked interior of the James Cook before it would start cycling. I was afraid the cycling time will be shorten due to higher ambient temperature, but for some reason not.
I leant a lot installing this AC with the goal to power it with the Honda in Eco mode. I have little reservation that I could not find an RV AC tech to do better.
One thing that I now know is since the trouble was short cycling, I can further tune the thermostat to lengthen the minimum off cycle time. It is easier to lengthen it than shorten it. I can reduce the thermal conductivity of the capillary tube by insulating a portion of it with heat shrink tubing if needed. I consider putting it in the return air stream instead but I think it would not regulate the air conditioning well. So far it is working very well in regulation.
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