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Old 07-14-2018, 05:36 PM   #13
Senior Member
Brand: Thor Motor Coach
Model: Vegas 27.7
State: California
Posts: 289
THOR #10907
Originally Posted by Long & Winding road View Post

Did you ever take a reading on the output temp? I would be interested to see what it shows. Have you run it all day (like 10 – 12 hours) straight like this? If so did it frost up at all.

Ok so I did a little testing for you... haha.

With an infrared heat gun it does show that the temps at the top of the evaporator are colder. It's not super accurate because I was shooting the thermometer at an angle since it wouldn't fit all the way inside. I didn't take the unit apart to verify which end the high and low side lines come in though. That would tell you exactly what areas of the evaporator will be colder. I've had AC evaporators freeze up, if I remember right they mostly freeze from the center and the edges are last to freeze. I've had aftermarket AC's stop all airflow and turn into a giant ice cube inside. No big deal, you just turn it off until it melts.

The edges of the core showed warmer, which makes perfect sense. Putting the probe at the absolute edges of the core could be a good idea.

I've ran mine for about 2 hours straight with no compressor cycling and it didn't freeze up. About a 90 degree day, entire coach in direct sun, inside coach temp was down to 67 degrees, (!!! It was pretty d@mn cold!) and outlet temps were in the very low 40's.

Your question about running it "all day- 10-12 hours" is my (and yours too) point in all this. If you have to run your AC non-stop all day long with no cycling to maintain a decent temp, something is wrong. It seems to me that Coleman is pretty conservative on their evaporator icing prevention strategies. I think they're cycling the compressor at temps that are way too high. Someone in this thread quoted Coleman's inlet and outlet temp specs, it's pretty weak actually as AC systems go. Automotive systems are much stronger of course, but getting ~40 degree outlet temps on a 100 degree day usually isn't a big deal. The "testing" specs on these RV units says something like a 20 degree temp drop is "normal"? F that. That's pretty weak.

My point is that you should NOT have to run the AC non-stop for 10 or 12 hours to maintain a decent inside coach temp. And if it's that hot and your (not "your" specifically, I mean everyone's in general terms) RV has that much heat loss, that means the AC's input temps are going to be way too hot to get the evaporator to freeze up even if you pulled the temp probe completely out of the core.

And yes, I have my temp probe (thermistor) hanging in the airflow in front of the evaporator, up inside the AC unit. I basically just wound it around the harness coming from the control module inside the inlet area.

For you other guys reading this, TRY IT. It's a totally reversible mod that takes about 2 minutes to do. There are tons of people on here complaining about AC performance. You've got nothing to lose trying this and it might just fix your issues.

I just put a link to this thread in the other AC thread talking about adding a vent. For those that try moving or removing the temp probe, remember that MORE airflow is better. Open ALL the outlets. Lack of airflow is what makes evaporator temps get too low.
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