R-31 Air Conditioner switching to heat

[OdyseaII]

The forward Dometic AC on our 2019 R31 CB switches to heat after running for a few hours for no reason I can understand.

With an outside temperature of 85+ here in Texas we run both ACs while on the boat with the thermostat set at 74. On two occasions the front AC has switched to heat after running the air about 6+ hours.

I was told this could be to make sure the unit is not freezing but the back AC does not do this and I am not convinced this is normal.

It seems to clear some time but I am wondering if this is normal or I have an issue.

I am wondering if maybe there is a problem with the temperatur sensor that feeds the unit?

Another thought is to re-program the control so the heat does not come one.

Any help or ideas would be greatly appreciated.

Thank you,
Keith
Odysea II
R-31 CB

 

[knotflying]

There is a setting to "defrost" the coil on a regular basis, but it is usually a short cycle. Another thought may be that the one AC is providing more cooling and the thermostat setting is on automatic. If the culprit unit ambient air goes below the set point then the heat will kick in. Thermostat location will affect the actual reading that the thermostat is getting. Even though you have them both set at 74 degrees the one unit's thermostat location may be reading higher temperatures and runs longer so that the area it is in cools to 74 when other areas it is cooling are actually cooler. Then the culprit AC may actually go off, the temperature goes lower than the 74 degrees by two degrees and then the heat kicks in. When troubleshooting it is always best to do one thing at a time. First I would check the settings on the culprit unit. Is it set to automatic and what is the set point that it will go to reverse cycle. I think you can change the degree differential. If so make it larger and see what happens. If that does not work then turn auto off and see what happens. If that does not help see what happens if you change the setting for auto defrost. I would suggest leaving auto defrost on. If you have high humidity and the unit runs excessively to keep up with the heat then the coil will frost up and that results in reduced air flow. When airflow reduces so will the cooling and then the unit will continue to run and the coil will continue to build up ice. Let us know how things go.

 

[OdyseaII]

Thank you KnotFlying for the response and the ideas on what to look at. I do realize the problem only when the two units are running so the one unit could be driving the other thermostat and culprit unit behavior.

I need to obviously begin by learning how to look at the programing of the unit.

Thank you again,

 

[HopTug]

If you haven’t tried it already, maybe close the door to the forward berth when both AC’s are running? I have found this to keep the AC from cycling to heat on our boat. Not sure where the sensor is for the berth AC, but I wonder if it isn’t getting blown on by the cabin AC

 

[OdyseaII]

Hoppy Trails,

Thank you for the note, in hindsight the door was open so I will try this.

Cheers,
Keith