A/C fans wont always come on when set to AUTO fan speed

[Relayman]

2017 3279 RS .
Reciently...my ac units have been acting up. if I run my a/c units in the COOL MODE, with the FAN
SPEED set to "AUTO", sometimes
the fan(s) will not come on, just the compressors. I can change the fan speed to low,medium , or high, and it works. fine.
Usually , when the temp diff rises enough to
call for the unit to come on, the fan will start first, then the compressor, but in AUTO fan speed....it the fan (s) do not always come on. This started in Galveston a few weeks ago.
Suggestions anyone ?

 

[Roller4tan]

First thing I'd do is check your connections behind the thermostat. Then if you get get into the ac unit from inside the rv check the connections there by unplugging and replugging them. There may be some oxide on those connections. It may also be the thermostat itself. My 2 cents

 

[Relayman]

thanks Roller...the ac units are not accessible from inside the unit...so up I will have to go !! could be the Galveston salt air did something I guess. but its odd it only effects the "AUTO" fan setting.

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[wdk450]

thanks Roller...the ac units are not accessible from inside the unit...so up I will have to go !! could be the Galveston salt air did something I guess. but its odd it only effects the "AUTO" fan setting.

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Don't you have an inside rooftop panel where the air goes in? This most common type of AC access panel has 4 screws under the corners of the panel under screw covers. Inside this inside access is a controller circuit board under a metal cover. On this circuit board ar relays (appropriate to your username) that actually switch on the fans and compressor. I would guess that you have an intermittent relay or board to fan electrical connection.

Here are some pictures taken off of the internet of the inside vent and the control box inside like on my unit.

 

[Roller4tan]

You have two ac units. Are they both controlled by one thermostat? Can you run each individually and do they both not work in auto?

 

[Relayman]

my 2017 3270RS has no
access from inside. Everything is in the roof mounted units ( whisper quiet units ( hah) ).
I have two thermostats. one for each unit.
Both are acting the same.

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[Roller4tan]

Very odd that both units react the same way. The salt air is definitely bad on electrical connections. If cleaning any connectors with a deoxidation product doesn't help, I guess it's time to call in the big guns. Call Heartland they may authorize a mobile repair to check the acs out, less the trip charge.

 

[Relayman]

Well, I think I may have found the issue. Inside the units is the "control box" that has the relays and communications board.
The new Dometic CCC 2
system uses CANbus communications via a data line between the thermostat (s) , and the control box. I checked the connection at the thermostat , which was fine, then , I found an RJ11 data connector that was not "snapped in" good, in the control box.
I reseated it , heard it click, and hopefully this takes care of the issue.
Fingers crossed.


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