I had some reservation in adding the variable speed function to the comfort air blower. I thought that since these rooftop RV AC have poor air flow path running the blower at near full speed is necessary to prevent the evaporator coil from freezing or create excessive compressor head pressure. Neither is good when you have a marginal generator.
I have also been not happy with the thermostat to allow me to set the target temperature since the AC would run at near 100% duty cycles - that is it runs for a long time and only cycle off occasionally. I would discover a capillary tube thermostat on an AC behaves quite differently since it is exposed to the cooling air stream. The more it is exposed to the air stream the faster the cycling. At some point this causes short cycling. A short off period is detrimental to the generator ability to restart the compressor due to excessively high head pressure, which in turn requires very high current requires to turn the compressor.
I would learnt that the blower speed control actually works in tandem with the thermostat in setting the target temperature. If I want the target temperature to be less cold, I need to set the blower speed lower. In fact the blower speed has more influence in the target temperature than the thermostat. Of course the other big variable is the heat gain of the camper from the outside.
Before I realize the significance of the blower speed I let the blower run at full speed during very hot days of 90s. The AC runs at nearly 90% duty cycle, which suggests if the ambient temperature goes higher slightly it will run continuously. But this changed when I can now reduce the blower speed.
I did some test with the blower speed set to minimum which gives a much more pleasure sound ambience.
On a 84F day in full sun (very high solar gain), here are some test results:
It should be noted that not all 84F days are the same. The intensity of the sun, direction, and the camper's orientation WRT the sun all make huge differences due to solar gain. Further, the humidity of the air inside and outside.
As you can see in the photo the duty cycle was roughly 75% and the AC was able to achieve ~ 72F inside. I should point out by that time the camper still suffered from heat soak of the day and my tests started after running the AC for about 1.5 hours to rid the heat soak thermal energy.
While this is the first time I bother to procure some ethanol free premium fuel, I found no perceptible difference in the engine tones when the compressor is on or off. I was expecting the generator engine to hunt as it does at near sea level when there is very little load running at Eco mode. It no longer hunts because of the 1,880 ft elevation which effectively derates the generator.
What I really pleased is to be able to achieve off time of over one minute by tuning the location and exposure of the capillary tube into the air stream. I found anything around one minute of more off time the generator has no problem restarting the compressor.
Update 2021/06/27:
I am dissatisfied with my inability to adjust some crucial characteristics of temperature control using the Kerstner mechanical thermostat. It just wouldn't allow the temperature to be set higher when I just want the cabin to be cool enough. I am also tire of having to tune the capillary tube's thermal transfer to get enough delay on the compressor restart. I decided to give this little temperature controller from China a try. This has been around for a long time and I have no excuse to buy one until now. For similar cost of a no name Chinese made mechanical thermostat I can have far more control of the parameters that are important. I decide to go with the AC powered version rather than the 12Vdc one to not incur phantom power drain on the coach batter as well as avoiding running wire for 12Vdc to the mounting location.
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