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a/c scs issues question - Printable Version

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a/c scs issues question - rvguy - 12-13-2025

Hope someone has had this issue and can walk me thru it.  both front and rear scs ac system wants to not go into cool mode on tstats.  Let me try and clarify. aquahot electric side switch in the a/c on position. when I turn on either a/c the heat light is all that will come on on the tstats even if I drop the temp to 60 degrees ( usally the symbol will change to the snowflake emblem). I have checked all circuit breakers in back as well as the ones on the left side in the cargo bay and all are good. I attached some pics.  Is there a relay somewhere that might have gone bad ( like when the aquahot is in electric mode and it shuts down the ac units). Problem just arose on this last trip out to california. I can turn the fans on for the ac units  and they work on low or high. If ya need more info let me know  tried to explain best I could.
       

RE: a/c scs issues question - [email protected] - 12-14-2025

(12-13-2025, 02:02 PM)rvguy Wrote:  Hope someone has had this issue and can walk me thru it.  both front and rear scs ac system wants to not go into cool mode on tstats.  Let me try and clarify. aquahot electric side switch in the a/c on position. when I turn on either a/c the heat light is all that will come on on the tstats even if I drop the temp to 60 degrees ( usally the symbol will change to the snowflake emblem). I have checked all circuit breakers in back as well as the ones on the left side in the cargo bay and all are good. I attached some pics.  Is there a relay somewhere that might have gone bad ( like when the aquahot is in electric mode and it shuts down the ac units). Problem just arose on this last trip out to california. I can turn the fans on for the ac units  and they work on low or high. If ya need more info let me know  tried to explain best I could.

Adam, I am not super familiar with this particular T-stat but I am quite familiar with the way the SCS units are wired, assuming your units are similar to mine. I would say it sounds like its a glitch in the thermostat. 

You may try disconnecting the power to the thermostat and reconnect it to see if you can maybe reset it. You can remove the red wire from the thermostat and that will remove power to the thermostat. Then connect it back and hopefully that will reset it. You may also look for a reset button on the thermostat. 

The thermostat pretty much acts on its own so if its not changing from heat to AC then its an issue with the thermostat for sure. The thermostat only sends power to relays to operate the heat or air, there is no feedback or any other interaction with the AC or heat.

RE: a/c scs issues question - rvguy - 12-14-2025

Already tried all that.  Whats funny is it does it on both ac tstats, and started at the same time. still wondering if its the relay that shuts the ac units down when the aquahot is on electric. Still investigating

RE: a/c scs issues question - Richard - 12-14-2025

Adam,

The relay kills all power to the SCS units. The fans would not come on. I agree with Jeff, this is a thermostat issue.

But, I here ya. If you wanted to isolate the problem you could hot wire the yellow tstat wire to the SCS to 12V. The compressor should come on, and the outside fan. Don't run it that way for long because the inside fan will not be running which will cause the compressor thermal to trip.

Another reason I think it is likely a tstat issue is the inside fans get one signal from the tstat , and a SECOND and separate signal to start the compressors.

All that said, no two Newells are alike and we do not know what a previous owner may have done. There are Coleman Mach tstats that will replace the SCS ones if needed.

RE: a/c scs issues question - rvguy - 01-01-2026

Replaced the thermostats with newer ones and Bamm...  We got a/c, not only do we have a/c its working better than ever. Thanks Jeff and Richard...

RE: a/c scs issues question - Richard - 01-01-2026

Thanks for reporting the solution.