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Old 04-16-2018
SAFCO SAFCO is offline
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Join Date: Aug 2017
Location: East Longmeadow
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Default LXI rooftop AC replacement walk through

The old original Dometic AC with heat strip is out and the new Dometic Penguin II 15k with heat pump is in. This thread is a compilation of my comments along with Stephen Mahan (mahansm). We both have LXi coaches and Stephen changed out his middle rooftop ac and invested a great deal of time I'm sure to write it up for the WOG. I've added only a few comments, most are Stephens words here.

Tools needed:
1/2" box end wrench
1/2" shallow socket, 8" extension, 3/8" impact driver
butt end connectors
wire nuts
electrical tape
phillips screw driver
5/16" nut driver
small straight screw driver with long reach (5" or so)
wire cutters
wire strippers
pen and paper
tape to label wires
needle nose pliers
flashlight
camera on the phone

Observations:
1. The units are heavy. Unless you spend a lot of time in the gym or similar, it's a two person lift. They're bulky, heavy, and fragile, not a good combination.

2. The roofs of our buses are high. If you don't have lifting equipment or something convenient overhead, it can be very interesting getting them on/off the roof. I ended up using an extension ladder against the side of the bus and a rope and pulley system. One end of the rope tied to the far goat rail, looped down through the pulley, and back up to me on top. It was still more fun than I really wanted to get it up over the goat rail and onto the roof. It's also congested up there, with antennas, fans, vents, generator exhaust, and similar. You need to preplan where stuff is going to go.

3. Dometic doesn't ship instructions with their unit and it's not real easy to find *current* instructions for *your specific model* on their website. In particular, the DIP switch settings are critical and can be made much more easily with the unit on the floor in air conditioned comfort with extra tools at hand. (#2 Philips, 5/16 wrench/nut driver, long skinny tool to poke the switch) (and glasses for us old folks that can't see up close any more.) I had to repeat the process on the bus roof because I used the wrong instruction sheet.

4. I was unable to find any documentation of the correct wiring of the unit and it's not at all obvious. Take good notes, trace each wire, and draw a picture as well as taking camera photos before you disassemble the old unit. Silly me, I thought I could easily figure out what went where. I had to pull the panel from the rear unit and trace that one out to figure out what went where.

5. Before attempting this, call Dometic with the exact part numbers of your existing units that will remain on the bus. There are three different thermostats (4, 5, and 12 button). Each thermostat has a corresponding version of the control board in the roof units and they are not mutually compatible. If you upgrade (like me) you must replace the control boards in the two remaining units or they will not function. Dometic help will provide the proper part numbers for the replacement boards. Be sure to pay attention to the DIP switch settings on the new board when you install them or you'll be back on the roof...

6. At least on my (Stephen) coach, the ceiling panels overlapped the metal frame that the securing screws pass through. It came out with a little persuasion but the ceiling panels adjacent to the unit had to come off to reinstall without risking tearing the material. My Millenial LXi was no issues, everything from outside.

7. The 4 button thermostat fits flush. The 12 button needs a 2" hole in the wall. Be very careful to not damage the cable with the hole saw. I used a 2 1/8 saw to give me a little leeway to properly center the new thermostat in the space.

I'm just happy it's done. (well, I still have to get up there and swap out the boards in the other two units...)

Since I searched the site for part numbers for the replacement boards for my old units and didn't find them, I'll post them here. This information is from Dometic as of today.
For old Dometic units PN 620315.321 that came with my '99 and used the 4 button thermostat, the boards to upgrade are:
5 button thermostat
3109229.009 (I have two for sale cheap, if anyone needs them)
10 (12) button thermostat
3312022.000
in addition, if you go to this (10 button) themostat you will also need a freeze sensor for each remaining unit. Part number for that is:
3312303.005

Dometic will sell you the boards directly but on the advice of the nice lady I spoke with I ordered them on line and saved about $60 for 2 sets.

Finishing the job of replacing the failed center AC unit and thermostat, I replaced the controller boards in the two old units.

Notes on the job:

0. Set the DIP switches on the new board to match what you have. You must set a switch for zones 2, 3, or 4, and also to tell it that it should control a zone of the furnace (Aqua-Hot), that it is a heat pump or that you have strip heat installed. It's much easier to do this at your workbench with unobstructed access to the board, good lighting, your glasses, lots of tools, and in AC. Not quite as easy on the roof of the bus.

NOTE: You cannot configure a heat pump unit to use strip heat.


1. Kill all AC power. Even though it's turned off at the control switch by the driver's seat, there's still 110 AC up there. (don't ask how I found out)(ouch). Either turn off the breakers in the bedroom or disconnect from shore power and either kill the inverters or disconnect the house battery.

2. Take it all apart. After taking off the cover (4 #2 Philips), remove the 2 5/16 hex screws covering the electronics box (forward, right side). All the hex screws are the same size. Remove the two screws securing the capacitor tray on the bottom edge of the electronics compartment. Remove the whole panel covering the evaporator assembly (yes, you do have to take it off).

3. Remove all the connectors (2 phone lines, 1 6 pin plug, 2 2 pin plugs. The 2 pin plugs are color coded (blue, white), and the phone lines don't matter which is plugged into which. All the connectors are polarized; they'll only fit the correct way.

4. Lift the capacitor tray up out of the electronics box. It's a tight fit and there are wires connected. If you are careful it will come out. Do not force it, find out what it's hanging up on and ease it out.

5. Remove the panel holding the circuit board. There are 4 nylon pins holding it on; you must compress a tab on one side of the pin so that you can slide the panel off the pin.

6. Now you can remove the circuit board from the panel. The lower left pin cannot be accessed (well, I couldn't get it) with the panel in place.

7. Replace the mounting panel onto the four pins and press until the pins snap into place.

8. Carefully transfer the black wires with the spade lug connectors to the new board. Be sure to put them in the same place that they came from on the old board.

stuart: On the two existing units I found the wires going to the new control boards route to the bottom of the board on the new board while they were higher on the old ones. This created a big problem because there was no slack in the wires. I was hoping to avoid cutting all the wire ties off the coach harness thats barely reachable with the unit still bolted to the roof but I might just have to do that.

9. Mount the new board on the 4 pins on the panel. Be careful; don't seat one until all are started.

10. Reconnect the 6 pin, the two 2 pin, and the phone lines.

11. Replace the capacitor tray and secure it with two screws.

12. Replace the electronics cover panel (yes, I know it was on top of the evaporator cover. The connectors from the new board are taller and it won't fit back the way it was.)

13. Fish the new temperature sensor (you did order this, didn't you?) up from below and poke it between a couple of the evaporator coils.

Stuart: One other issue is I did not see anywhere to plug the new temp sensor for de-icing so I left it out. Of course this gave me an E5 error on the new 12 button thermostat. That issue is less urgent since I understand the heat will work fine just no AC until that is installed. The plug from the bus must be in the bundle of wires all zip tied together.

14. Replace the evaporator cover. It won't fit flush over the electronics compartment. Do the best you can; some metallic duct tape will cover the gap. (Again, no issues on the Millenial LXi unit)

15. Replace the unit cover.

16. Connect the white connector from the new temperature sensor to the two pin connector that was dangling and was run in the bundle with the phone lines.

Turn power back on, reset your thermostat, and bask in the new cool air.
Stephen Mahan
Lynn Haven, Florida
1999 LXi 43 dual slide
850 814 9022
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Stuart Fearn
East Longmeadow, MA
2000 LXi Millennium Edition, Single slide
stuart@safcofoam.com
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  #2  
Old 04-16-2018
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Randy Dupree Randy Dupree is offline
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very nice write up.
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2000 LXI 43
Bainbridge,Ga.
Archer Fl.
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  #3  
Old 04-16-2018
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SNOWBIRD SNOWBIRD is offline
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Explain the freeze sensor. Is this a failsafe to turn on the AH zone if the temp falls below some preset level? Or is this start some sort of defrost cycle if the A/C unit freezes up?

And how do like the new thermostat compared to the old one? Mine originally came with a 4 button but the PO changed it out for a 5 button thermostat. I'm not happy with it, but it may be quirky because he didn't know what he was doing and just installed the wrong one without upgrading boards. I had my front A/C freeze up on me recently so I may just change that one out and do this same thermostat mod.
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1998 43' LXi #F119728
Lansing, Michigan
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  #4  
Old 04-16-2018
mahansm mahansm is offline
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The freeze sensor is inserted into the evaporator coil and measures the temperature. It allows the control board to cut power to the compressor and prevent evaporator freeze-ups. I think that it's a thermistor but have no hard evidence of this. I suspect that if Bluebird didn't run the 2-pin connector wires down into the plenum in the passenger compartment you could plug a sensor directly into the board and route the sensor wires to get to the coil.

This sensor has no connection with Aqua-Hot or strip heat function; that is controlled through the thermostat mounted elsewhere in the bus.

Having no experience with the 5 button thermostat, I can't comment on the difference between it and the 10 button unit. However, it's a great improvement over the 4 button unit. The functions are much more intuitive and it adds the ability to program different temperatures for different times of the day. It also adds quite a lot of display functionality. The 10 button unit also supports "auto" mode, which will control AC, heat pump, heat strip, and Aqua-Hot functioning without user intervention. Set the desired temperature and the 10 button will keep your bus there.

Default temperature settings for this are AC above 72 and heat below 68.
These can be reset and single mode operation can be selected for each zone.

Please note that the Dometic Penguin units will not support both heat pump and heat strip operation in the same unit. They will also not run more than one mode of heat in one zone at the same time. There's a priority built in and the heat pump will run before the Aqua-Hot is triggered; Aqua Hot is run when outside temp drops below about 35 F.

The 4-button has many more functions than it has buttons. This means that the user must learn which button combinations and sequences are needed to access a given mode. The 10 button unit splits out a good deal of this functionality and the increased information on the display gives feedback on what you're actually doing with your button presses.

This leads, of course, into a long discussion of human/computer interfaces.
For further reading, I recommend "The Inmates Are Running The Asylum".
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Lynn Haven, Florida
1999 LXi 43 dual slide
850 814 9022
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  #5  
Old 04-16-2018
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SNOWBIRD SNOWBIRD is offline
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That sounds good. Does the upper cover off of your old unit fit the new one or will the new cover need to painted to match?
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1998 43' LXi #F119728
Lansing, Michigan
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  #6  
Old 04-16-2018
mahansm mahansm is offline
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Well, it's complicated. When I bought the bus it had three original fiberglass covers that were painted. While trying to repair my dead center unit I saw that all three covers were cracking badly around the mounting holes. I purchased and installed three new white plastic covers, discarding the three old fiberglass covers.
The new unit also came with a white cover but it is much more stylish, with ventilation holes in the sides of it towards the rear. I now have mismatched white covers up there; front and rear plain white and center sculpted white with speed holes.
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Lynn Haven, Florida
1999 LXi 43 dual slide
850 814 9022
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  #7  
Old 04-16-2018
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SNOWBIRD SNOWBIRD is offline
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So probably the old covers don't fit on the new units?
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1998 43' LXi #F119728
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  #8  
Old 04-16-2018
SAFCO SAFCO is offline
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I'd have to guess the new covers do not fit the old units. Not positive.

I had the same finding on my bus in that the other two old covers were cracked and looked sketchy around the 4 mounting holes. I'm pretty cheap so I'm thinking I'm going to fabricate a patch of aluminum and rivet it on.

I really have not looked at the bus to see if the new unit stands out by being bright white vs the others painted gold.
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2000 LXi Millennium Edition, Single slide
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  #9  
Old 04-16-2018
mahansm mahansm is offline
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I'm not all that concerned. I've got three white AC covers, a white Fantastic Fan cover, a white satellite dish antenna, and a white TV antenna. Since I'm not entering it in the Concours D'Elegance at Amelia Island any time soon, I don't really see a major problem. Besides, the white covers give me lower heat gain in the sunshine than covers painted another color and I do live in Florida. Actually, in cold weather in darkness, they also radiate less heat than other colors...
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1999 LXi 43 dual slide
850 814 9022
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Old 04-16-2018
Clembo Clembo is offline
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My center air would not come on and after 2 days of searching I found a corroded connection in a 2x4 junction box inside up in the return vent next to the ac. Kinda hard to get to. Sits sideways. Works great now. Make sure it's really broke before you replace it.
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