Hello, new to RV life and this forum.Recently my wife complains that our thermostat doesn't shut off properly. It did keep the heat on one time until we were cooking (way above set temp). [ dometic duo therm comfort control center with phone plug connection]I finally bought an inexpensive replacement on Amazon. [White Rodgers 1C20-101 Economy 24 Volt/Millivolt Heat Thermostat] And thought it should work for our heating/cooling needs.Last night I traded it out by cutting the wire with the RJ-8(ish) plug and connected the wires to the new thermostat, following the chart provided by new thermo mfg.It did not work.So I re-connected the phone plug to the original cable and inserted back into our Dometic CCC thermostat, and nothing. No backlight screen or anything.Note: while I was trying to connect the new analog thermo the Red and Green wires touched long enough to smolder and melt some insulation.I'm willing to take common 'you did what?'s' in replies in my ignorance, but don't forget to provide a possible solution.thanks in advance

Aurcor, If you cut through the "RJ" cable with a single cut, it is almost certain that you blew a fuse back in the unit. Matt

1. YOU DID WHAT:B2. You cannot install a normal Tstat in place of the Dometic CCC system. 3. Those wires you cut are NOT regular tstat wiring. They are a 4 wire communication cable. The Tstat end plugs into the wall tstat. The other end will plug into the roof AC control board. 4. You MUST use a Dometic wall tstat. If you have a 4 button Doimetic you have to replace with a 4 button. BUT the 4 button was discontinued almost 18 years ago and no new ones available. The 5 button replaced the 4 button and IS available. The newest is the 10 button which is NOT compatible with your older control board unless your unit is newer than 5 years ago and may have the 10 button.5. Odds are when you cut the cable end off you blew the 3 amp fuse on the upper AC control board. That is why you have no display when you spliced the wires back.5. Now, since you did not state year/Model/Brand of RV and how many AC units, the wall tstat may NOT be the temp sensor. The Dometic system has the option of remote sensors and IF there is a remote sensor connected to the upper AC control board, the wall tstat will not be the temp sensor. Doug

Me thinks you need an RV tech to repair this. Your knowledge is lacking as you are in this position.

thanks all. it is a 97 Mobile Scout 33RK We don't really use the AC but am going to need to get heat going asap. Overnight temps already dipping to low 30's.There is only one AC. I did check the only fuse I could see in the heater compartment, and it was not blown. I found some CcC units on Amazon (4 to 5 button) If those will work i will purchase one of those. First I would like to check the sensors (?) and see if I can't get the backlight going again on the old one. and I can re-terminate the cable with the plug so there is no funky splicing. I will let you know how it goes.CJ

I'm pretty sure that fuse Doug mentioned is in the control box with you capacitors in the rooftop unit under the outer cover and inside the electrical box. I don't believe you can switch to a five button thermo without also changing the upper control board to match the 5 button thermo. Also the phone style control cable is NOT a phone cable, the ends are REVERSED, so be sure to duplicate the cut off end when you reattach the plug. Good luck, Dave

dometic thermo prob | Good Sam Community

aurcor
Explorer
Oct 24, 2019
thanks all.

it is a 97 Mobile Scout 33RK We don't really use the AC but am going to need to get heat going asap. Overnight temps already dipping to low 30's.

There is only one AC. I did check the only fuse I could see in the heater compartment, and it was not blown. I found some CcC units on Amazon (4 to 5 button) If those will work i will purchase one of those.

First I would like to check the sensors (?) and see if I can't get the backlight going again on the old one. and I can re-terminate the cable with the plug so there is no funky splicing.

I will let you know how it goes.

CJ
cavie
Explorer
Oct 23, 2019
Me thinks you need an RV tech to repair this. Your knowledge is lacking as you are in this position.
dougrainer
Nomad
Oct 23, 2019
1. YOU DID WHAT:B
2. You cannot install a normal Tstat in place of the Dometic CCC system.
3. Those wires you cut are NOT regular tstat wiring. They are a 4 wire communication cable. The Tstat end plugs into the wall tstat. The other end will plug into the roof AC control board.
4. You MUST use a Dometic wall tstat. If you have a 4 button Doimetic you have to replace with a 4 button. BUT the 4 button was discontinued almost 18 years ago and no new ones available. The 5 button replaced the 4 button and IS available. The newest is the 10 button which is NOT compatible with your older control board unless your unit is newer than 5 years ago and may have the 10 button.
5. Odds are when you cut the cable end off you blew the 3 amp fuse on the upper AC control board. That is why you have no display when you spliced the wires back.
5. Now, since you did not state year/Model/Brand of RV and how many AC units, the wall tstat may NOT be the temp sensor. The Dometic system has the option of remote sensors and IF there is a remote sensor connected to the upper AC control board, the wall tstat will not be the temp sensor. Doug
Matt_Colie
Explorer II
Oct 23, 2019
Aurcor,

If you cut through the "RJ" cable with a single cut, it is almost certain that you blew a fuse back in the unit.

Matt

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