Dometic A/C only cools for 3 minutes but fan continues to run: Generator only

[JMF]

We have a 2019 Thor Siesta 24SJ and have run the A/C fine under 30Amp shoreline. When we run the A/C on the diesel generator, it turns on very cold for about 3 minutes and then the compressor appears to shut down, but the fan continues to blow. When we turn the A/C off and back on it cools again for a few minutes. The controls for the temp are on the Firefly Multiplex Console.

We have a low profile Dometic A/C and an Onan 3600 Diesel Generator 13.5K BTU.

Does anyone have any ideas?

[jtyphoid]

Maybe the Firefly is shedding the load. Do you have your fridge or water heater on electric?

[JMF]

Neither the fridge nor the water heater are on. There isn't any other load on the generator.

Thanks!

[ducksface]

Do you have an inverter?
My ac runs through my inverter... On purpose as an experiment.

If my batteries are bad, the ac does just what you said. It won't even run on shore power with bad batteries.
Two new batteries cured my problem.

If you don't have an inverter... I'm out.

[JMF]

I don't think we have an inverter. The house batteries are good. They are topped up via the solar panel and last time I looked they were at full power.

Thanks!
J

[jtyphoid]

Have you checked the AC voltage being provided by the generator? Is it holding steady when the compressor starts and runs?

[javelin]

Originally Posted by JMF

We have a 2019 Thor Siesta 24SJ and have run the A/C fine under 30Amp shoreline. When we run the A/C on the diesel generator, it turns on very cold for about 3 minutes and then the compressor appears to shut down, but the fan continues to blow. When we turn the A/C off and back on it cools again for a few minutes. The controls for the temp are on the Firefly Multiplex Console.

We have a low profile Dometic A/C and an Onan 3600 Diesel Generator 13.5K BTU.

Does anyone have any ideas?

The attached link sounds like your same problem except it occurs on both shore and gen. I only read a few entries but they were pointing to the Firefly system. I did not read all entries but I know from other posts on this Forum that Firefly techs seem very good in returning calls and helping. Might be worth calling them to see if they have a solution or suggestion for a setting change on your |Firefly system.


2018 interstate TB Firefly a/c issue - Airstream Forums

[JMF]

No, haven't checked the voltage but we are suspicious that it might be the problem. How do we check that?

Thanks!
J

[JMF]

Firefly already fixed one issue today - the Generator option was not selected and that stopped the AGS functionality from displaying on the screen. Thought that it might fix the AC but it didn't. Good suggestion and plan on calling them back to see if they have any ideas. Will also try and find a 30A outlet we can hook up to, to ensure that the AC is still running on shore power. Read the link you attached- interesting, similar issue but that one occurred on both generator and shore.
Thanks, J

[JMF]

Update: Talked to Firefly this morning and super impressed - they believe its a known issue and are sending an update to us.

Thanks everyone for your help, I will let you know for sure that its fixed when we get the part installed.

J

[JMF]

Originally Posted by JMF

Update: Talked to Firefly this morning and super impressed - they believe its a known issue and are sending an update to us.



Thanks everyone for your help, I will let you know for sure that its fixed when we get the part installed.



J

Well, we had the software upgrade from Firefly and it did fix the Auto function. But the ac compressor is still switching off after 2 minutes. Firefly are sending an air con module box which sits inside the ac unit in the ceiling. Hoping that it will fix the ac problem.

Incidentally, we found out some info in the process of changing out the Firefly screen. For those Siesta/Citation/Synergy owners, if you have a diesel generator, there is no AGS option available. The LP generator does have an AGS option. Something that neither the sales & marketing documentation nor the Salesmen explained. It would have been nice to know.

[JMF]

It wasn’t the Firefly module after all. The freeze sensor had worked it way out and was causing this. After it was “fixed” it started happening again. It was an intermittent problem with the same 2 min shutdown. Turns out the electrical insulation on the freeze sensor was compromised and the thermistor inside was occasionally shorting. New freeze sensor fixed everything.