AC Question For Doug

That is correct. I had to tie into a 12V wire for a ceiling light which Grand Design had pulled close to the location There was also a 115V wire there. This is standard on Grand Design units prewired for a 2nd AC.
Anyway... Here's an update.
As stated above, the thermostat has functioned correctly since installation. It appears that the LED segments and backlight function correctly when the room temp hits 70 or lower. Anything above 70 and the brightness of the LEDs and backlight become close to the samebrightness and the Tstat is barely readable.
I'm going with a bad thermostat. Wierd,,

When the OEM supplies a prewire, they rarely connect the 12 volt POS and NEG to a power source. Doug

Several things to look at. The 12V wires were provided by the manuf. and were already in place, as was the thermostat cable. The thermostat came with molex connectors so I had to cut those off and butt connect to the t-stat cable. I was able to match colors so there was no confusion there. We did check for proper voltage on the 12V wiring they provided. I'm going back this weekend to double check everything. Thanks to all for all of the info.

There are some RVP systems that utilize 8 volts to the tstat from the upper control board and THAT is normal. BUT only for the older mechanical wall tstats and not for more current LCD display. What I would do in your case is remove the Tstat and add 2 wires from the POS and NEG and connect to a Volt meter and see if the voltage drops from 12 volts when you experiance the DIMMING. IF NOT, then I would say the tstat is bad. If it does drop you have a bad ground or POS connection somewhere. Even the minimal milliamp draw of the tstat LCD causing a volt draw would be amazing to cause a bad connection to cause the volt drop. But, I guess it can happen. Maybe your GROUND to the tstat is NOT a real ground. Another way, is to run a 2 wire connection from your 12 volt fuse center and connect 12 volt POS and NEG at the Fuse center and run to the tstat to verify a GOOD voltage connection. You stated YOU did not run the tstat wires. Doug

Flute Man wrote:

Bob Landry wrote:
Just curious.. What is the significance of 8.1V? What would create that particular voltage?

Yes 8.1?
Jerry

Two shorted battery cells?
Minimum voltage for the tstat?

Inquiring minds what to know!

Bob Landry wrote:
Just curious.. What is the significance of 8.1V? What would create that particular voltage?

Yes 8.1?
Jerry

Just curious.. What is the significance of 8.1V? What would create that particular voltage?

Try this. Make SURE you have 12 volts and NOT 8.1 volts. Doug

https://www.airxcel.com/DesktopModules/RvProduct/Pdf/t005.pdf

dougrainer wrote:
Never seen this. WHICH RVP Tstat do you have. They have about 20. Doug

It's the 9430*340. It's a cool only thermostat. It came with Molex plugs but I had to cut them off and butt connect to the control cable. It was the only Cool Only t-stat I could find,

Actually, I'm not enjoying it any longer. I traded a few months back for a Grand Design fiver.