rear ac in the bedroom has no 12v

[Himcules]

Hello gang.

been a while. rv had been in storage the past 6 years and i finally got it out and restoring service to it. changed oil, filters, house batteries, lubed the chasiss and the sliders, etc everything is working except the rear ac unit.

how the control cable is wired is front rj11 flat 4 wire cable goes to the rear unit. rear unit's 2nd rj11 cable goes to the center of the coach where the thermostat is. so if the rear unit isn't working, the thermostat won't display anything. that's how the thermostat controls both units (up to 4 zones as long as daisy chain the control cables to each other and the final one goes to the thermostat.

anywas, thermostat display was dead. thermostat is powered by that cable with 12v. i verified i had 110v ac power in both units. front unit had 12v in the brown and white wires. rear unit did not.

So i move the thermostat to directly connec to the front unit. and it works fine.

rear unit not getting 12v power is my issue. Does anyone know where the fuse and relay for this thing is at?

front of the coach fuse box (where the generator release is) has the 3 fuse boxes and one of them does say "ac bed rm" with a 15 amp fuse. i changed that anyways and that fuse junction does get 12v through it.... but still out of luck with 12 at the brown and white wires in the rear unit's wiring.

tia!

[Lincman983]

Have you checked the comm wire (RJ11) for any breaks or kinks? I would use a short test cable and possibly use the T-stat to see if the A/C unit powers up that way. If that doesn't work then it may be an issue with D/A converter box. There is a 3 amp fuse inside the "brain box"

[Himcules]

Originally Posted by Lincman983

Have you checked the comm wire (RJ11) for any breaks or kinks? I would use a short test cable and possibly use the T-stat to see if the A/C unit powers up that way. If that doesn't work then it may be an issue with D/A converter box. There is a 3 amp fuse inside the "brain box"

Thank you! It's a bit windy today so I'll wait till the wind dies down before climbing on the roof to pull the covers off and take a look at the 3amp fuse. I wish there was an led light blink for diagnostics like on home hvac systems...

I have a new cable tester kit from amazon coming in tomorrow to test the other cable just to make sure. But when I use the "good" cable thats running from the front to the rear and connect the thermostat to the rear end, that cable is good. when i use a coupler to bring the signal back on the 2nd cable, it doesn't work so might have a problem with the 2nd cable (which i will verify once the cable tester comes in).

will report back tomorrow when the tester is in and the winds are calmer here.

[Himcules]

Just to update everyone. Everything is fixed.

found that a mouse had found its way into the coach and made a nest in the upper media cabinet (next to the bathroom). the upper cabinet has a false floor and a false side. removing 4 screws to the side revealed the cable bundle and all you. the floor of the cabinet just lifts up and you can see that there is a hole drilled at the bottome left corner to run the communication cable to the location where the thermostat is installed. there's a pic that shows the telephone cable (communications cable) that goes under the false floor of the cabinet to the center of the coach where the thermostat is.

the mouse had chewed thru 2 of the 4 cables plus the ground (white) that ran to the rear AC unit.

it is impossible to pull that cable out as the conduit into the roof is full of wires. so i just cut the rj11 communication cable off and added a cat3 phone jack.

used my cable tester to make sure the pins were right. the cat3 jack made it easy to switch around the pins to get it perfect.

both ac units are working perfectly again.