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Old 09-26-2022, 07:33 PM   #1
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HVAC Modules not communicating

Hello - 2022 Berkshire 45CA. Something happened today and all the ACs stopped working. In poking through all the systems power, power seems good all around. Breakers are ok, shore power ok etc.

In poking through the Precision Plex menus, I got to the HVAC Diagnostics menu and see the HVAC Modules are all red. According to the manual this means the panel canít communicate with the modules.

So question that follows now is where are these modules and how do I get them communicating again?
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Old 09-26-2022, 09:38 PM   #2
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So after about 3 hours, things came back online. All modules are communicating and ACs are running

Glad that’s fixed but I would like to learn why. I tried HVAC Reset about and hour before it stopped working. This is supposed to help reconnect missing modules. Does it just take an hour? What can cause modules to lose communication?
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Old 09-27-2022, 06:42 AM   #3
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After encountering several problems with our HVAC system, I've become very familiar with how it works . This is a very long answer to your question, but my experiences might help you troubleshoot future issues.

Each A/C unit has a comm module mounted inside the shroud - on ours, they're mounted on the front of the ac unit just inside the seam where the two pieces of the shroud come together. Each module has an in and out port, allowing them to be "daisy chained" together. They're connected by 6-wire data cables with RJ-12 connections (like a phone jack). The first in line will be your bedroom ac, then the mid, and then the front. The interface with the Precision Plex system is on the left side of the back of the circuit breaker box under the bed - lift up the bed and you'll see several RJ-12 ports on the left side, one of which will be marked HVAC.

Our first issue was the failure of the number 1 comm module in the bedroom ac. I was able to get things working again by swapping the #1 and #3 modules - apparently the failure involved the #1 module being able to receive/process signals but not pass them along. Precision Plex replaced the failed module under warranty after we got home.

After that, things were ok for a while but then I started to see what you describe - the system would lose comm with the ac's for a while and then would reconnect. At first, it only happened once in a while and although we had it looked at, we couldn't reproduce the problem. Over the last year, it became more common and it finally completely quit this past May. Turned out to be a bad/shorted data cable somewhere in the wall between the interface and ac #1. I hope that's not your issue - we ended up having to fish a wire through the wall and then drill a hole in the roof to pass the cable through in order to avoid taking the entire inside ceiling down.

Here are a couple of other useful tidbits:

1) You already found the diagnostics page for the HVAC system. If you ever need to swap out any of the comm modules, you'll need to perform a reset to get the system to recognize/correct which module is on which ac unit. If you don't do the reset, the modules will retain their original positions (i.e. swapping front and rear will cause the panel controls to operate the front ac when you change the rear settings and vice versa). You can also test the individual functions (fan, heat pump, ac compressor) from that page. By the way, the reset process takes a few seconds, definitely not an hour plus.

2) In addition to the diagnostics page, you'll also find a page where you can add offsets to each of the temp sensors in the RV. In our 45A, the front sensor is mounted in an area that gets quite warm on sunny days causing it to read higher than the true temp. I added an offset to that sensor to keep the front ac from running constantly.

3) When the outside temp drops below ~45, the front and rear ac units will "lock out" since the heat pumps won't function in temps that cold. The lockout not only prevents use of the heat pumps, but disables the fans as well. I hate that feature because we run the fans at night for white noise (and to help circulate the heat from the aquahot / heated floors) and to keep our dogs from barking at every noise. You can still run the fan on the mid-ship unit since it doesn't have a heat pump.

4) When our data connection between the interface and ac units finally failed completely, we were on the road in 90+ degree temps (of course!). I discovered that unplugging the data cable from the interface (even through the cable was shorted) resulted in all three ac units turning on full blast cold. We were able to get through a couple of days leaving the data cable unplugged and using the circuit breakers to turn the individual ac's on and off as needed. I ordered a 6-wire cable from Amazon and ran it out the bedroom slide and across the roof to get the system working again. Thank goodness for duct tape

I hope that helps!
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Old 10-02-2022, 04:49 AM   #4
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Did you ever find out where the lockout temp sensor is?
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Old 10-02-2022, 07:27 AM   #5
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Did you ever find out where the lockout temp sensor is?
According to the multiplex system layout Forest River sent me for my coach, the outside temp sensor is behind the Forest River logo/nameplate next to the main door.
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Old 10-03-2022, 08:22 AM   #6
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Thatís good to know but raises the question, why there?
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Old 10-03-2022, 06:04 PM   #7
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anaviator - first of all thank you so much for the information. It took a couple days for me to make the time but I finally poked around under the bed. I don’t see the same RJ-12 connections there you’re describing. What year is your 45A?

I did discover a the coach fuse box and third Precision Plex control panel here tucked neatly behind a false panel. Also a fan or something for the aquahot.

How did you get the multiplex system layout from FR? Is it model and year specific?
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Old 10-04-2022, 04:50 AM   #8
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Our 45A is a 2020 so it is entirely possible that there have been changes to the system and connection points since then.

I requested the spec sheets from Randy Alwine in the warranty department. He'll need your VIN (or at least the last 7 digits of it) to pull them. The specs are actually VIN-specific. Our coach, for instance, is an early 2020 and has a mix of 2019 and 2020 features.
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Old 10-04-2022, 07:34 AM   #9
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Anaviator is correct. The prints are model and year specific. If you PM your VIN I can see what prints are available for the year and model of coach
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Old 10-07-2022, 12:12 PM   #10
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I'd like to add one note to the excellent post by Anaviator and that is the PC modules he spoke of within each AC unit are supposed to be mounted upside down in order to prevent moisture from collecting. When my units failed a few months back and the diagnostic showed no communication (red) it was the morning after a rainstorm where the wind blew the rain sideways and water got into the metal shrouding.
When I took everything apart on the rear AC unit I found the module was laying loose on the roof face up and it was full of water. The other two units were also laying on the roof upside down but were dry. After thoroughly cleaning and drying everything the unit worked just fine. I mounted each of the 3 modules ( I have 3 AC units) upside down on the metal shroud with double sided tape and sealed all of the seams with duct tape. No issues since.
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Old 10-12-2022, 01:27 PM   #11
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I'd like to add one note to the excellent post by Anaviator and that is the PC modules he spoke of within each AC unit are supposed to be mounted upside down in order to prevent moisture from collecting. When my units failed a few months back and the diagnostic showed no communication (red) it was the morning after a rainstorm where the wind blew the rain sideways and water got into the metal shrouding.
When I took everything apart on the rear AC unit I found the module was laying loose on the roof face up and it was full of water. The other two units were also laying on the roof upside down but were dry. After thoroughly cleaning and drying everything the unit worked just fine. I mounted each of the 3 modules ( I have 3 AC units) upside down on the metal shroud with double sided tape and sealed all of the seams with duct tape. No issues since.
I finally got up on the roof today as the HVAC stopped working again. Seems my only motivation to work on this is when things are broken

In our case, all three modules are loose inside the shroud, all three facing up. The front AC unit module full of water. It's been like this for a while as there is a lot of corrosion. I disconnected that and now the rear and middle ACs are working again.

@Mccowboy - the seams you sealed up -- these the ones round the metal "lid" you had to open to reach the modules? Or somewhere else?
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Old 10-12-2022, 01:37 PM   #12
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I finally got up on the roof today as the HVAC stopped working again. Seems my only motivation to work on this is when things are broken

In our case, all three modules are loose inside the shroud, all three facing up. The front AC unit module full of water. It's been like this for a while as there is a lot of corrosion. I disconnected that and now the rear and middle ACs are working again.

@Mccowboy - the seams you sealed up -- these the ones round the metal "lid" you had to open to reach the modules? Or somewhere else?
YIKES! The modules are just loose inside the shroud? On mine, each module is held by a screw perpendicular to the ground with the front/face of the module facing forward. The front of the module is coated in plastic to make it water resistant, but I can't imagine they're designed to be sitting in a puddle of water. If I were you, I'd use some double-sided tape or a screw to secure them in place like mine are.
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Old 10-12-2022, 04:56 PM   #13
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YIKES! The modules are just loose inside the shroud? On mine, each module is held by a screw perpendicular to the ground with the front/face of the module facing forward. The front of the module is coated in plastic to make it water resistant, but I can't imagine they're designed to be sitting in a puddle of water. If I were you, I'd use some double-sided tape or a screw to secure them in place like mine are.
Correct, loose inside the shroud. One was kind of wedged underneath a bracket. But definitely no screws. I will absolutely be mounting these as you describe.
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Old 10-19-2022, 02:31 PM   #14
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The seams around the entire sheet metal shrouding I sealed with duct tape.
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Old 11-02-2022, 09:23 PM   #15
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Update on my situation…. I spoke with the folks at Precision Plex and they sent me a new HVAC module to replace the broken one up front. All ACs working fine. I also mounted them vertically so we wont have any further issues with water sitting in the module. Definitely a QC miss on our unit.
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