rear A/C dead

[JimM68]

My rear a/c seems to be completely dead, no fan, no cool, no heat pump.

System is a pairof Dometic Penguin roof a/c's, a pair of atwood furnaces, and a dometic 5 button controller.
Rig is a monaco dp (08 knight)50 amp with ems. Rig is plugged in, and all the lights on the ems are on, indicating all circuits are powered.

The controller is working fine. It see's bothzones, and indicates what I tell it to do. both furnaces work, front a/c works. rear won't even give me "fan only", indicates on the controller but nothing happens.

I'v checked the fuses, and reset the circuit breaker for the rear ac.

I'm figuring my problem is no ac power to the rear a/c. (becauseif there was a 12 volt or pcb problem, the 5 button controler would not "see" the rear zone.

Any suggestions where to go next?
I'm thinking I need to open up the a/c distribution panel.....

[JimM68]

Thanks Dennis, I'll put that on my list, it does sound like a likely point of failure. If I had a washer/dryer, a proper fix would be higher on my list, but as it is, I think I'll just relabel the breakers and call it done.

[codelld]

Jim,
There is a good possibility that the circuit board connection for the relay has over heated and it now does not make a connection. If you remove the EMS circuit board check for a bad connection were the relay is soldered to the board. I had a couple of relays that did this and I just bridged the circuit board trace with a piece of wire. If that is not the problem you can bypass the relay by putting the 2 connections for the relay on the same terminal connections.

[dougrainer]

Davidlatham2012 wrote:
At the dealership, Ive had to unplug the 12v system completely on these zone control themostat for a hour or so and reconnect. It resets it. I would try it

Sorry, 12 volt disconnect will have NO affect on a Dometic Zone control other than you losing your previous presets for temp and auto/fan function. What you CAN do is do the Dometic CCC reset, but that will not fix a dead CCC display or operational problems. The reset ONLY confirms the DIP switch settings on each Zone control board. Doug

[tkcas01]

Congrats on the work-around! Whenever I have an electrical glitch, I always fear the EMS might be dying. Probably not cheap to replace. As you have isolated the problem to one of the circuits in the EMS, if it were me, I'd do a little research to see if this is potentially a "contained" failure or the sign of other problems ahead. If the later, better to deal with it on your time table rather than have a complete failure while on the road. Otherwise, I would say happy RVing!

Good luck some more!

[JimM68]

ok, that worked. rear a/c is running again. Looks like I have a bad load channel in the intelletec 750 ems.

As I don't have a washer dryer and never will, not sure how much I care?
The load is still on the same leg of the 50 amp.

Anyone else see any real reason to dig deeper or fix better?

[JimM68]

Still looking for a schematic for an intelletec 750 EMS.

If Iam "seeing" things right, I Have power coming off the "rear AC" breaker into the ems board. It "appears" there are 8 black wires going into the ems board, four hots off the breakers into 1,3 5, & 7, and four goung "Out" 2,4,6 & 8.

When I open the water heater breaker, I lose power on 1 and 2.
rear ac breaker killls power on 3, never any power on 4
washer dryer breaker kills power on 5 and 6
front ac--- 7 & 8

As Ido not have a washer dryer, I am going to swap the wires between 4 and 6.

This will move the hot for the reatr ac from a non functional output to the output intended for a washer dryer I don't have, and hopefully restore power to the rear ac.

wish me luck.

[tkcas01]

Davidlatham2012 wrote:
At the dealership, Ive had to unplug the 12v system completely on these zone control themostat for a hour or so and reconnect. It resets it. I would try it

Welcome to the forum! As an RV technician you have surely dealt with more issues than any one RVer and your experience should be very helpful here! I see you have been busy since joining yesterday! 😉

[Davidlatham2012]

At the dealership, Ive had to unplug the 12v system completely on these zone control themostat for a hour or so and reconnect. It resets it. I would try it

[tkcas01]

The best I can do is report a couple of issues I had that may give you some ideas.

A few years ago I got a spark and smoke out of my front unit and it stopped working. Turns out one of the wire nuts connecting it to power must have not been put on tightly, got hot, melted and caused a short. So it might be possible one of yours could have "jiggled" loose but you were saved the fireworks. On mine, the electrical connection is in a junction box accessible when you take the filter out of the grill.

Last year my compressor would run, but the fan would not run unless I gave it a quick spin to get it started. This pointed to the capacitor. On mine there were two and I replaced them both and it works fine now. So you could also have a capacitor problem.

Could also be the thermostat or its wiring come loose, but I've never had to deal with that.

Good luck!