Can AUTO mode damage A/C from frequent shutdowns?

[wopachop]

Have a dometic air conditioner with the wall mounted controller. The A/C reacts differently based on the FAN setting being low, high, or auto.

If the fan is set to low the A/C runs 24/7 on the low fan speed and i can hear when the compressor kicks off and on.

If the fan is set to auto the A/C will bounce around between running on high, low, or completely shutting off.

I have heard A/C guys say you need to let it rest for several minutes after a shutdown. It seems like my RV rooftop A/C can turn off and on within a minute. It also sounds like a long pause of nothing when it switches between high and low fan.

To battle this i set the controller temp super low so the A/C stays running. But i would prefer if i could set it to 85F when im gone. Not sure which of the fan settings would do the least amount of wear and tear on the ac unit.

[dougrainer]

This is for Dometic that have 3 speed fan. Doug

A. Auto Fan
When “AUTO” fan is selected, the fan speed will vary depending on the difference
between the temperature set-point and the room temperature. In “AUTO” fan, the
compressor and fan will cycle ON and OFF with the thermostat.
When the difference is:
8 °F / °C or more The fan operates on HIGH
5 to 7 °F / °C The fan operates on MED
4 °F / °C or less The fan operates on LOW

[dougrainer]

kellem wrote:
Perhaps I misunderstand but never heard of AC adjusting fan speed on its own.

Ours is as follows.
High constant
Low constant
Auto high
Auto low.

Depends on the system. Dometic, on AUTO, the AC compressor is ON and if more than 5 degrees diff, the HI fan will come on. Once the AC gets closer or less than that 5 degree, the Fan will "shut" of for a second and then restart on LOW and once temp is reached will shut both Compressor OFF and the Fan OFF. From your desciption, you have a RVP(Coleman) wall tstat. And yours operates as you state. This is for the LCD Coleman tstat. Doug

Set Fan Speed for Cooling Mode
1. Place the slide switch in the COOL position.
2. Pressing the MODE button will toggle through the available speeds.
• “COOL AUTO” setting allows the speed to vary depending on the cooling needs which
is the default setting.
• “COOL HIGH” or “COOL LOW” setting will set the fan speed to run continuously at high
or low, but the upper unit will cycle when cooling is needed.
• “FAN HIGH” and “FAN LOW” setting will set the fan to run continuously at high or low
speed. The upper unit will not run to produce cooling. Setpoint is not adjustable in this
mode.
•

[dougrainer]

cavie wrote:

3 tons wrote:
Perhaps member Doug can enlighten us a bit more, but from what I know about my Coleman Mach 1, regardless of the fan mode, etc. once the compressor cycles to Off there is a 3 min time delay before the compressor can restart again, this to allow time for the high-side of the compressor to equalize (or bleed down) to the low-side, however can’t say whether this attribute is driven by the air conditioner or by the t-stat...

3 tons

the time delay starts when the uni has been TURNED OFF. it will not try to cycle it's self in just 3 min. if you turn it off or the power goes out it will not restart for ten min. not 3.

Where do you get this 10 minute delay? I constantly in service shut power OFF or turn the AC OFF and never have had a 10 minute delay. Doug

From Dometic.

. Compressor Time Delay
A time delay of approximately 2 minutes occurs any time the compressor is required
to begin the cooling or heat pump cycle.

[Cummins12V98]

Fan in the on position is good because the air is constantly moving and not having to cool down the ducts when kicking on. I leave my fan in the ON position it gives more even temps.

[kellem]

Perhaps I misunderstand but never heard of AC adjusting fan speed on its own.

Ours is as follows.
High constant
Low constant
Auto high
Auto low.

[cavie]

Fan on auto means when the compressor reaches the set temp it will turn off. in auto the fan will turn off also. Hi or low it will run all the time. My trailer and my house are set this way. I can cool my trailer to 70 degrees. If your compressor is short cycling then you are low on Freon.

[cavie]

3 tons wrote:
Perhaps member Doug can enlighten us a bit more, but from what I know about my Coleman Mach 1, regardless of the fan mode, etc. once the compressor cycles to Off there is a 3 min time delay before the compressor can restart again, this to allow time for the high-side of the compressor to equalize (or bleed down) to the low-side, however can’t say whether this attribute is driven by the air conditioner or by the t-stat...

3 tons

the time delay starts when the uni has been TURNED OFF. it will not try to cycle it's self in just 3 min. if you turn it off or the power goes out it will not restart for ten min. not 3.

[wa8yxm]

I run my ducted units on high full time..
But as others have said
When the COMPRESSOR shuts off.. 3 minutes for the pressure in the system to bleed down to stable before you re-start.

The blower however is not so hampered. pressure normalizes in like An instant (<1Sec)

But the constant change in noise level is annoying so I run them on HIGH full time. that way the noise is more constant and is rapidly filtered out by my mind. I actually have to pay attention to tell that it is running.

[dougrainer]

time2roll wrote:

Second Chance wrote:
When it "seeks" between high and low fan, it's the fan shutting down - not the compressor. If you listen, you should be able to hear that. It's irritating but shouldn't do any damage. When those conditions occurred in our previous rig, I would just put the fan on high full-time and let the compressor cycle on and off as needed. The Coleman Machs in our new rig are set up differently, though.

Rob

+1

The high and low speeds are different windings in the fan motor and one needs to be off before the other is energized.

A hot day mine usually will jump to high and stay the rest of the day. After sundown it may cycle up and down a few times as OP indicates until it settles for low for the rest of the night. I have no concerns.

Bingo, The fan shuts OFF temporarily between fan speed changes, Normal and a common question. Doug

[time2roll]

Second Chance wrote:
When it "seeks" between high and low fan, it's the fan shutting down - not the compressor. If you listen, you should be able to hear that. It's irritating but shouldn't do any damage. When those conditions occurred in our previous rig, I would just put the fan on high full-time and let the compressor cycle on and off as needed. The Coleman Machs in our new rig are set up differently, though.

Rob

+1

The high and low speeds are different windings in the fan motor and one needs to be off before the other is energized.

A hot day mine usually will jump to high and stay the rest of the day. After sundown it may cycle up and down a few times as OP indicates until it settles for low for the rest of the night. I have no concerns.

[DancinCampers]

When the outside temp gets in the hi 80's, I switch my units from auto to hi. This results in a more even cooling as the air keeps moving when the compressor turns off.

IMO, the only excessive wear on the fan motor not running on auto will be in the bearings.

Short cycling of the compressor will normally trip the internal overload device. If this happens a lot you could damage the overload to the point it may not reset.

Also, short cycling results in higher than normal amp draw, and this could damage the start cap/device.

[Second_Chance]

When it "seeks" between high and low fan, it's the fan shutting down - not the compressor. If you listen, you should be able to hear that. It's irritating but shouldn't do any damage. When those conditions occurred in our previous rig, I would just put the fan on high full-time and let the compressor cycle on and off as needed. The Coleman Machs in our new rig are set up differently, though.

Rob

[3_tons]

Perhaps member Doug can enlighten us a bit more, but from what I know about my Coleman Mach 1, regardless of the fan mode, etc. once the compressor cycles to Off there is a 3 min time delay before the compressor can restart again, this to allow time for the high-side of the compressor to equalize (or bleed down) to the low-side, however can’t say whether this attribute is driven by the air conditioner or by the t-stat...

3 tons