Question on Dometic A/C and thermostat

[Socaldave]

Was in my TT on Sunday and being a little warm out I set the A/C at 74f. System fired up and ran for about 20 minutes and then the fan stopped for about 15-20 sec then came back on with the compressor still running (I could hear it). Ran for another 5 minutes or so and did the same thing. The T/S was on auto for some reason (I always run it on Hi Mode) and when it came back on both times and it seemed to be running in low mode. By then it had reached the set-point and shut off. I had finished what I was doing and turned it off and went back in the house. We're headed to pretty warm area (100+) next week for a few days and I want to make sure I don't have any A/C issues in that heat.
We have not had this TT long and first trip out a few weeks ago it performed flawlessly in warm weather.

Is that cycle normal?

TIA

[sourdough]

Sounds normal to me. That cycling is the reason I won't leave the bedroom A/C on auto.

[jsb5717]

Sounds normal to me as well. In ours it seems that when the AC stops and starts in Auto mode that it's change from Hi Fan to Low Fan...back and forth depending on what it's sensing. I'm not sure if that's what it's really doing but that's the assessment I've come up with to explain it.

[JRTJH]

It is normal. The thermostat function drives the fan speed when set to AUTO:

High speed if the sensed temperature is greater than 5 degrees higher than the set temperature and low speed if the sensed temperature is less than 4 degrees from the set temperature.

When the sensed temperature reaches 5 degrees of the thermostat setting, the fan shuts off, switches to LO and resumes operation. The compressor continues to run (to prevent a high/locked rotor condition). If the sensed temperature rises after the fan is on LO, as soon as the difference is greater than 5 degrees, the fan will shut off, switch to HIGH and resume operation.

The air conditioner will continue this "back and forth fan speed" as long as the thermostat senses a rising/falling temperature. Typically this only happens when the air conditioner can not sustain the falling temperature until it reaches the set point.

If the conditions are right for the air conditioner to continue dropping the room temperature, when the thermostat reaches the set temperature, the compressor will shut down, the fan will continue to run for about 15-30 seconds (to push the cold air out of the ducting to prevent condensation from forming)....

All of this is "bypassed" if the fan speed is set to HIGH or LO. But the fan will always run for a few seconds after the compressor shuts down.

[Socaldave]

Thanks for the confirmation all, I didn't know the cycling when in auto as I have only ran it on high before. I was comparing it to a household central A/C system.
Headed to the lower river next week so let's see if this unit will keep it tolerable in 105f+ heat.

[sourdough]

Good luck on that trip! Just realize that 105 is pretty hot for one AC - or 2 or 3. I figure it's a 13.5k on that size rig. If you have some Reflectix put it in the sun side windows and keep the shades down - that hot you might put it in all the windows because the heat will just radiate through them. Take some fans to push the air around.

[Socaldave]

Originally Posted by sourdough

Good luck on that trip! Just realize that 105 is pretty hot for one AC - or 2 or 3. I figure it's a 13.5k on that size rig. If you have some Reflectix put it in the sun side windows and keep the shades down - that hot you might put it in all the windows because the heat will just radiate through them. Take some fans to push the air around.

Yeah I've got all that planned.
We have been going to the river for 38 years now but mostly in smaller 19' or cab over campers. Looking at the extended forecast it's calling for low to mid 100's. Just hope it is not like this past week when it was 117-119 with a low of 92!