Originally Posted by
Jon Wehrenberg
This is personal experience only so take it for what it is worth.
Based on where my units are I set each for slightly different temps so the interior of the coach feels at a uniform temperature. That may be because the front with its abundance of glass needs a different setting than a midship unit. It may also be because the relationship of the return air to the supply air is such that the SMX control needs a different setting because on one some of the chilled air is being returned and on another the return air is less affected by the supply air.
Also, keep in mind our SMX units can be calibrated and it might be each has been calibrated slightly differently.
Going further without looking at the data such as the temperature spread between supply and retunr air it is unknown if the units are working to the same level of efficiency, and if not that would also impact their set point to maintain comfortable temps.
As to the question about the aft unit cooling the bedroom with the door closed you don't mention if the engine has been running or if there are any other factors which will impact that unit's ability to cool.
If you measure the temperature spread on all your units you answer in part a lot of what you are quesitoning. You know immediately if your units are working properly. Then since the thermostat sensors are likely in the return air flow you can measure the temperature at which point the units cycle, compare their respective set points and temperature readings and you will know if the calibration is correct. If not recalibrate the temperatures. Then you have to look at variables such is sun pouring in through the front windows? Has the engine been running, is supply air being drawn back through the return? Are the filters clean?
If you use an IR gun, then as Jack suggests you can get a sense of the operation of the units by getting the suction line temps (the line that is at the condenser and is sweating). If they are wildly variable you can probably assume you need to adjust the R-22 Freon charge to maximize the efficiency.
There are so many variables and data reference points the best place to start is by making sure the basics are known and are correct. The temperature may be 75 degrees, but the Cruise Air control might be seeing that as 70 degrees and obviously that shuts the unit down prematurely so pull out the book and the IR gun and start with some good temperature checks and calibrations if required. Unless you have done the calibrations you are trusting they are correct.