False zone temp reading for front AC unit

[RollingHome]

Hello Everyone!

My first post here and I'm hoping someone has an idea what could be causing this condition.

I have a 2021 Montana 3855BR Legacy with the in-command system. It appears that this years model uses Coleman Mach air units. The problem I'm having is that the front A/C unit will not turn on at all. If you select fan, auto, manual it thinks about coming on for a brief moment, then right back to off. One interesting thing to note is that the zone temp is displaying 0 degrees. The
other unit displays 74 degrees and is working.

I'd be interested to hear what everyone thinks.

[Carl n Susan]

Bump to be seen.

[M&M]

If it has worked before, I’d try :
Resetting
1) Press and hold the Power Button until the display gives you an option on screen to ​Power Off​ - press this.
2) Once the display is completely black, exit the vehicle and find the BCM.
3) Remove the cover of the BCM to expose the green board.
4) Press and hold the Reset button for 2 Seconds and let go.
5) Press and hold the Power button until the display shows light.

Step 1 and 5 is like a reboot. Try that next time. If that doesn’t work, then try the reset on the board.

[SLB]

You could check and see if the thermostat wiring is connection is loose. It fixed one of mine which did the same thing.

[RipNC]

It is possible the wires from the remote temp sensor have come loose or broken. In the attached photo the red and white (next to each other) are the sensor wires. If resetting iNCommand doesn't work I'd check those wires at the unit (have to open up to get to the control board).

One other possibility is the wires to the Gateway (also in the unit). These are small wires in a 4 pin molex connector and I have had one that broke off at the molex.

[ExPatNW]

Hi everyone,

I want to open this thread up again. I am struggling right now with the same intermittent problem with our front AC not switching on. In-Command (which I love btw) shows 0F (sometimes other random and incorrect temperatures) – when its clearly not that temperature in the bedroom, so In-Command does not tell the AC to come on.

The dealership is unable to repro the problem, although recently when we went back to pick up the rig the problem occurred (I was happy about that) so they did see it happen. They have checked the cabling (so they say) and the thermistor – all ok. My feeling is the gateway is faulty, but unless they can “prove” its faulty, they won’t replace it.

Basically, I have been told there is no problem, if it happens again I just need to switch everything off, disconnect the battery, disconnect from shore power and then restart it all.

Frankly I find this unacceptable. Imagine being told when your car AC fails to just pull over on the freeway, switch off, wait 5 seconds and then start up and go again. Why do I have to accept this as “normal behavior”.

So (sorry for the rant) I would love to know how many people are routinely restarting their rigs to get their front ACs to communicate to In-Command.

BTW – Opened a ticket with ASA – interested to hear their take on this, hopefully get a response early next week.

Our rear AC has worked flawlessly since we had the unit (2021 3790RD Legacy).
Happy Camping!

[ChuckS]

The gateway for that Zone has a relay that is intermittent ... If all the wires to the gateway are connected and no corrosion, etc on any of them then the gateway is of course the prime suspect.

The temp remote temp sensor can be tested by YOU if you have a multimeter and basic electrical skills... simply go on the roof if this is a ducted system and remove that Zone AC cover and locate the gateway and remove remote temp sensor and measure the resistance of the sensor versus the inside temp.

If the reading is within range then the sensor is ok...

If the Zone that you are having issues with is ZONE 2 then there is also an EOL... end of line resistor that tells the In Command RV-C chain that it is the last item in the loop//

If that EOL is bad ( resistance has changed ), or the EOL is loose where it plugs in at its molex plug connector then you will also have issues with that Zone

READ THIS LINK to educate yourself on the In Command RV-C for the Coleman AC units

It will also show you exactly where you will find the EOL

https://asasupportdocs.blob.core.win...3%20NCSP35.pdf

[ExPatNW]

Thanks - super helpful. The cabling and EOL resistor has (in theory) been tested, so its a simple solution in my mind, replace the gateway.

[ExPatNW]

@ChuckS - sorry - one further thought, which I wondered if you might have an opinion on. My problem is not that In-Command cannot tell the AC to run, rather the data from the gateway is erroneous, so In-Command never thinks it needs to tell the AC to come on. In my mind, the relay may be more likely to get the AC to run, nothing to do with sending the digital temperature value back to In-Command over the bus. So this would imply it is a gateway error but perhaps not specifically to do with relay? Would you agree?

[ChuckS]

Originally Posted by ExPatNW

@ChuckS - sorry - one further thought, which I wondered if you might have an opinion on. My problem is not that In-Command cannot tell the AC to run, rather the data from the gateway is erroneous, so In-Command never thinks it needs to tell the AC to come on. In my mind, the relay may be more likely to get the AC to run, nothing to do with sending the digital temperature value back to In-Command over the bus. So this would imply it is a gateway error but perhaps not specifically to do with relay? Would you agree?

I would be curious if you have checked to see if you have the latest firmware installed ?

Also .. you stated the remote temp sensor for that Zone was verified ok... Verified how?
** To verify the remote temp sensor is actually working one needs to disconnect the other end of the remote temp sensor cable plug at the gateway and then ohm across the two wires and compare the resistance reading of that sensor against the temp inside at that remote temp sensor location.

The BCM and Display require that resistance feedback so that the analog signal from that temp sensor can then be interpreted by the system to display the temp at the sensor... This in turn is then compared to your actual set point temp and then the AC, HP, or furnace is commanded to run depending on the temp read, temp set point and inside temp at that zone

** If that Zone Temp is reading 0 degrees then either the remote temp sensor is bad, had a staple in the two wire harness somewhere, etc.

** If you REMOVE the remote temp sensor plug at the Gateway then the Zone temp displayed should now display a temp reading of -- F for degree temp because it cant see that sensor...

** If the display however still shows 0 degrees then the gateway is sending erroneous data

This is how I think one can narrow down the issue

** If you had a new remote temp sensor you could simply plug in the new sensor at the gateway and the temp for that zone should now read something other than zero...

If it does not then you know the gateway is at fault...
https://www.amazon.com/Coleman-83303...79b61bbf47e157

[ExPatNW]

Thanks Chuck - again very helpful - I wish you were the tech at our dealership! You clearly understand the process of fault finding (isolating individual components, testing, replacing etc to narrow it down to a specific component).

Right now I have not tested the CAN BUS cabling or thermistor myself -but have been told that the dealership tech has done this.

I may well buy a replacement thermistor and test as you suggest above if the dealership route stalls (which I fear it may now). I might just buy a gateway too for that matter. Being without the front AC in a hot area is just not doable, the rig needs at least 2 ACs to get it comfortable (and I know many opt for 3 - and I can understand that).

My thanks to you sir, and this forum.
Chris