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Old 06-30-2013, 03:40 PM   #1
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Dometic Duotherm ACs not working at all

I'm getting desperate because our AC units are not coming on at all -- no fan, no nuthin' -- just the "EE" error code on the thermostat.

We purchased this low miles 2003 Holiday Rambler Endeavor 38PST back in December, and never checked the AC due to the winter season, although they supposedly worked. It had been sitting maybe for one year, although it was plugged into house current at the dealership.

It has front and rear Duotherm Dometic 13,500 BTU AC units. (I do not know if they are heat pumps or not -- how do you tell?)

When I went to turn on the AC now that it is summer and we're wanting to start using the MH, the AC units will not turn on. I get an "EE" message on the thermostat. Here is what I have found and done so far -- to no avail:

1) The thermostat reads "EE". When I try to reset per usual instructions, it momentarily flashes "FF", but when the two buttons are released, it goes back to "EE."

2) A mobile technician said it was the thermostat. We replaced the thermostat -- NO CHANGE.

3) There is measurable 12V DC power at both units.

4) There is measurable 110V AC current at both units using the generator (7.5KW).

5) The RJ-11 lines from thermostat to front AC and from front AC to rear AC are all good (per the line tester).

6) Per Dometic 800-number Help Desk, the on-line tech said it was the control boxes on the units. I purchased two new control boxes (BTW, best prices, by far, are on EBay -- $72.50 incl shipping!!). HOWEVER, replacing the control boxes did nothing! The thermostat still reads "EE" even after trying to reset.

Can the dip switches somehow be incorrect, or would this not affect at least one of them running?
Can low Freon cause them to not run?
Why both went out at once??

Thanks for any help. Reached frustration saturation point.
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Old 06-30-2013, 03:56 PM   #2
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Both at once is the clue. Each is on a separate leg of your 50A shore connection, so you must have 120V on each leg. You have a system problem, not an individual unit problem. Mobile tech's advice to replace tstat & its result should tell you much about the tech. I've swapped tstat's coach to coach & gotten the same error as method of eliminating tstat as the problem.
Tstat appears to be reading a problem on its inputs.

I'd guess its a simple connection or a chaffed wire bundle w/a cross connect. You will find a mess of connections in the ceiling cavity below the units; kill 120V & 12V repress and re-twist all connections taking care as if working on live connections not to accidentally ground anything or to become a ground connection between live parts (unless of course you fully test all connections prior to messing w/em). I'd start this w/the front AC, as it has the control board that enables the rear.
There may be a blade type 12V fuse on the control board w/in the unit, check if its blown.
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Old 06-30-2013, 04:18 PM   #3
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Confirm 12 and 120 volts at ac unit.

Verify correct dip switch setting on control board

Marry control board to thermostat, done viz thermostat, search for instructions as cannot remember now.
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Old 06-30-2013, 05:45 PM   #4
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Quote:
Originally Posted by EngineerMike View Post
Both at once is the clue. Each is on a separate leg of your 50A shore connection, so you must have 120V on each leg. You have a system problem, not an individual unit problem. Mobile tech's advice to replace tstat & its result should tell you much about the tech. I've swapped tstat's coach to coach & gotten the same error as method of eliminating tstat as the problem.
Tstat appears to be reading a problem on its inputs.

I'd guess its a simple connection or a chaffed wire bundle w/a cross connect. You will find a mess of connections in the ceiling cavity below the units; kill 120V & 12V repress and re-twist all connections taking care as if working on live connections not to accidentally ground anything or to become a ground connection between live parts (unless of course you fully test all connections prior to messing w/em). I'd start this w/the front AC, as it has the control board that enables the rear.
There may be a blade type 12V fuse on the control board w/in the unit, check if its blown.

THANKS. So the only problems HAVE to be within the AC unit or the RJ11 cord between thermostat and unit, right?
The entire control unit was replaced.
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Old 06-30-2013, 05:46 PM   #5
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Quote:
Originally Posted by TQ60 View Post
Confirm 12 and 120 volts at ac unit.

Verify correct dip switch setting on control board

Marry control board to thermostat, done viz thermostat, search for instructions as cannot remember now.
That's what I was wondering -- whether the dip switches are the confounding factor. Are there dips on the thermostat?
Are the dip settings found on this forum?
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Old 06-30-2013, 08:37 PM   #6
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What button control do you have 4 button or 5 button?
If you changed out the control units you may need the 5 button.
In QT's 1&2 both manuals are on the link plus what dip switch's that need to be operated.
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Old 07-01-2013, 07:58 AM   #7
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Quote:
Originally Posted by 007";1624959]What button control do you have 4 button or 5 button?
If you changed out the control units you may need the 5 button.
[URL="http://www.irv2.com/forums/f103/original-part-1-and-2-quick-tips-and-easy-mods-18509.html
In QT's 1&2[/URL] both manuals are on the link plus what dip switch's that need to be operated.
It's a 5-button -- same as what was originally on the MH; no change from that.

Will check dips.
Thanks.
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Old 07-02-2013, 03:54 PM   #8
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Error code "EE" is a communications error between the thermostat (the 5-button CCC) and the control box (the box above the air filter). It is NOT an error beyond the control box .... in other words, the topside units (compressor/capacitors/evaporator/etc) are not at fault. The thermostat is powered by the 12vdc line that comes from the control box back to the thermostat (via the telephone cable). It's possible the ground between the thermostat and control box is bad ... or the 12vdc line bad (low voltage). You might try a new short telco cable (you can remove the thermostat and move it right next to Unit #1 for trouble shooting. Should be 12vdc between red and black at thermostat.

BTW, although the communication cable (telco cable) may test good, it is polarity sensitive. In other words, check the Duo Therm schematic for location of the color coded wiring within the end plugs of the cable.
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Old 07-02-2013, 04:21 PM   #9
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How hot is it? Our first trip out, we got an error code (think it was EE; don't remember for sure) because it was over 110 F. The solution was to hold a handful of ice by the thermostat until it cooled down to 110; then the air came on and everything was fine. Good luck!
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Old 07-02-2013, 04:31 PM   #10
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YEP! It was a chaffed RJ11 wire, about 5ft from the AC unit itself. ONLY one of the wires in the 4-wire cable was cut thru. It's possible that it was chewed. The outer black covering seems to be nibbled for a 1" section, and ONE wire was cut thru (See attached pics).

In addition, the RJ11 wire between front and rear AC units showed that one wire in the 4-wire bundle is not intact, but I have not pulled that wire out. I simply bypassed it.

By bypassing both RJ11 cables, I got both AC units working again.

Unfortunately, I'm out $340 for the "RV Technician's" time (he's the one who said it was the TStat, and then that it was the control boxes -- and then he left); $100 for a new TStat; and $150 for two new control boxes. TOTAL $590, almost enough for a whole new AC unit. Hard lesson, but not one that I was not previously warned about.

In retrospect, many people had said to check the RJ11 lines as a likely culprit -- altho most said to just go ahead and replace control boxes as likely to be the ultimate culprit. It's just that when I tested the lines (AFTER the "RV Tech" left with my $340) my RJ11 tester was showing lights, but I did not know how to interpret them. 3 lights were lit, but I should have been checking for 4 lit lights -- that one broken line resulted in 3 lights only; Yes, the RJ11 tester works well!
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Old 07-02-2013, 04:38 PM   #11
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Quote:
Originally Posted by baloo View Post
YEP! It was a chaffed RJ11 wire, about 5ft from the AC unit itself. ONLY one of the wires in the 4-wire cable was cut thru. It's possible that it was chewed. The outer black covering seems to be nibbled for a 1" section, and ONE wire was cut thru (See attached pics).

In addition, the RJ11 wire between front and rear AC units showed that one wire in the 4-wire bundle is not intact, but I have not pulled that wire out. I simply bypassed it.

By bypassing both RJ11 cables, I got both AC units working again.

Unfortunately, I'm out $340 for the "RV Technician's" time (he's the one who said it was the TStat, and then that it was the control boxes -- and then he left); $100 for a new TStat; and $150 for two new control boxes. TOTAL $590, almost enough for a whole new AC unit. Hard lesson, but not one that I was not previously warned about.

In retrospect, many people had said to check the RJ11 lines as a likely culprit -- altho most said to just go ahead and replace control boxes as likely to be the ultimate culprit. It's just that when I tested the lines (AFTER the "RV Tech" left with my $340) my RJ11 tester was showing lights, but I did not know how to interpret them. 3 lights were lit, but I should have been checking for 4 lit lights -- that one broken line resulted in 3 lights only; Yes, the RJ11 tester works well!
The good news is you are now an A/C communications guru ... and your A/C works !!

BTW, if the old T-stat is actually OK you could wire it as an independent T-stat for the bedroom. All you need is 12vdc at Unit #2 and run a short telco from Unit #2 to the new bedroom T-stat. Totally independent and no more fumbling around and wandering down the hall in the middle of the night for adjustment.
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Old 07-02-2013, 04:39 PM   #12
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Follow up with that RV tech...
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Old 07-02-2013, 04:57 PM   #13
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Follow up with that RV tech...
He's one of the mobile ones. I should have objected before I paid -- or better yet, I should have clarified payment terms before he started.

He started this mobile business 3 years ago, and told me he made so much money that he started his former brick and mortar business. I guess preying on susceptible RVers -- especially those caught away from home in parks -- is very good business. They called it highway robbery back in the 1700's.

Not much changed in the world over the millenia.
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Old 07-02-2013, 10:37 PM   #14
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He's one of the mobile ones. I should have objected before I paid -- or better yet, I should have clarified payment terms before he started.

He started this mobile business 3 years ago, and told me he made so much money that he started his former brick and mortar business. I guess preying on susceptible RVers -- especially those caught away from home in parks -- is very good business. They called it highway robbery back in the 1700's.

Not much changed in the world over the millenia.

Not that I'm excusing the high rates but, unfortunately, most owners (a generality) simply aren't prepared for the complexity of today's RVs. The more we (owners) want in the RV, the more "stuff" the manufacturers cobble together and cram into inaccessible areas. Do we really "need" 4 TVs in a motorhome ?
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