AC seems to have a mind of its own?

[starkruzr]

So I have a 2013 Flying Cloud 25, which I think has the 15K BTU AC unit. I have my AC set to 55 (mostly to get it to remove some humidity) and it seems to run the compressor for a while, blow super cold for a few minutes but then turn off the compressor for like 7 or 8 minutes. What's going on?

[starkruzr]

Here's the setting on the thermostat and the temperature it's measuring.

[starkruzr]

It's also kicking the fan up to "hi" from the "lo" setting I have it at when it decides to turn its compressor off without being asked!

[GMFL]

Sounds like the Run Cap is bad.

[BayouBiker]

The thermostat is digital and uses a control system algorithm. when the temperature difference is that great it has stability issues and gets what we call reset windup. depending on how the firmware was developed, it could do unpredictable things.

Try setting the temperature to 4 degrees colder than actual and tell me if it does the same thing.

edit: turn it to 4 degrees colder, then turn it off and then back to cool and auto fan. Honestly I think you have found a firmware bug.....

[starkruzr]

Originally Posted by GMFL

Sounds like the Run Cap is bad.

Can you expand on that a little?

[starkruzr]

Originally Posted by BayouBiker

The thermostat is digital and uses a control system algorithm. when the temperature difference is that great it has stability issues and gets what we call reset windup. depending on how the firmware was developed, it could do unpredictable things.

Try setting the temperature to 4 degrees colder than actual and tell me if it does the same thing.

edit: turn it to 4 degrees colder, then turn it off and then back to cool and auto fan. Honestly I think you have found a firmware bug.....

Have just tried this. Going to let you know what happens -- but I just noticed that when it does it's "high fan and I'm going to turn the compressor off" thing, an hourglass shows up on the display.

[BayouBiker]

Single phase (120V) motors need a capacitor to shift the lagging electromagnetic coils out of phase from the leading ones so the motor will turn. He is suggesting the capacitor is bad. It is most likely not the issue. Generally a capacitor ether works or it shorts out. Since your compressor runs for a bit the capacitor is most likely fine.

[starkruzr]

OK. It's still doing it, fwiw, and doing the hourglass thing -- which it seems is a compressor delay to keep from short-cycling the compressor (probably good as a safety feature).

[BayouBiker]

the hourglass is part of the controller code that tells you it is intentially disabling the compressor. If humidity is very high it could be the evaporator is icing. and it is cycling off to prevent that.

edit: if it is icing I see from the manual it sets the fan to high also. Could be the sensor is messed up.

[starkruzr]

It's still possible to keep it comfortable in here, so I'm not super worried about it yet. If *I* set the fan to high, it seems to run normally, or close to it. (This is after doing a reset/init according to the docs.) I'm going to add this to the list of things I need looked at when I get to Austin, though.

[BayouBiker]

OK going back to your original description where you say it' super cold, I'm going to guess that you have managed to ice your evaporator by setting the temperature so low. It will take about an hour to thaw it out so set it to high fan and just let it run if you are using the trailer, move the temperature one degree at a time till you get it to where you want it.

I think everything is fine you just iced the evaporator. once it thaws out it will be fine. In the future don't set the temperature so low when the humidity is high, Instead move the temperature one ore two degrees at a time and let it rest a bit.

[starkruzr]

Okay, thanks. That makes sense. It didn't do this in 85 degree heat with pretty high humidity in FL.

[BayouBiker]

I think the lower outdoor temp along with very high relative humidity was just the magic combination. The lower outside temp made the compressor very efficient and allowed it to get the coils below freezing, the extended run time plus the icing compounded the issue. It takes a perfect storm to ice the evaporator good like you have. I managed to ice my 5 ton home AC once in 25 years on a similar 75 degree super humid day. Took nearly all night to thaw it out. It was one big hunk of ice because it did not have an icing sensor like the Dometic. happy camping!

[OTRA15]

Originally Posted by starkruzr

So I have a 2013 Flying Cloud 25, which I think has the 15K BTU AC unit. I have my AC set to 55 (mostly to get it to remove some humidity) and it seems to run the compressor for a while, blow super cold for a few minutes but then turn off the compressor for like 7 or 8 minutes. What's going on?

Good advice, Brian and GMFL, and an interesting thread . . . thanks.

Just wondering . . . if a free-standing dehumidifier, in the shower maybe, would reduce the water-removal work being asked of the A/C on a 55F setting?

Also, assuming that a new dehumidifier is online, what about setting the A/C fan speed manually to either High or Low [whatever is required for an acceptable room temp], and then tracking how often the compressor kicks on/off . . . this might reduce the variables under consideration?

Thanks,

Peter

[overlander63]

IF the evaporator coils ice up, and if you have a heat pump:
turn off the unit for a couple of minutes, then turn it on Heat Pump. That will reverse the circulation of the refrigerant, making the evaporator coils warm, and helping to melt the ice.

[BayouBiker]

good call on the Heat Pump idea, only run it till air blows out lukewarm.

A dehumidifier, won't help. It's the total energy load combined with a fairly low outside temperature that brings on icing and the dehumidifier just adds to the in trailer heat load as it trades dryness for warmer air plus the 20% efficiency loss. The biggest contributor to icing is a long continuous run cycle due to a large temp differential on the thermostat setting, and high humidity simply makes it take that much longer to cool to the setpoint. The best way to avoid icing is cooling a couple degrees at a time, or go with Terry's plan which may even be a better idea....

[Wazbro]

A dehumidifier would help a lot since the OP stated he set the temp low mostly to get rid of humidity (as in no reason to set AC so low for temp).
Just a bit of info on RV AC systems with built in thermostats (not remote thermostat) usually can only be set down to 70 or slightly less for cooling to prevent icing.
EDIT: having the fan on high will reduce icing.

[BayouBiker]

Okay I stand corrected....

[OTRA15]

Originally Posted by Wazbro

A dehumidifier would help a lot since the OP stated he set the temp low mostly to get rid of humidity . . .
. . .

That's what I thought, but I deferred to Brian's recent post to the contrary.

Originally Posted by BayouBiker

. . .
A dehumidifier, won't help.
. . .

Originally Posted by BayouBiker

Okay I stand corrected....

Thanks,

Peter