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 > Can AUTO mode damage A/C from frequent shutdowns?

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lb

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Posted: 07/31/20 12:03pm Link  |  Quote  |  Print  |  Notify Moderator

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.

3 tons

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Posted: 07/31/20 12:40pm Link  |  Quote  |  Print  |  Notify Moderator

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

Second Chance

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Posted: 07/31/20 01:24pm Link  |  Quote  |  Print  |  Notify Moderator

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.

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DancinCampers

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Posted: 07/31/20 01:50pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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time2roll

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Posted: 07/31/20 01:59pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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dougrainer

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Posted: 07/31/20 03:03pm Link  |  Quote  |  Print  |  Notify Moderator

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

wa8yxm

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Posted: 07/31/20 04:55pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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cavie

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Posted: 07/31/20 08:55pm Link  |  Quote  |  Print  |  Notify Moderator

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.


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cavie

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Posted: 07/31/20 08:59pm Link  |  Quote  |  Print  |  Notify Moderator

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.

kellem

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Posted: 08/01/20 09:03am Link  |  Quote  |  Print  |  Notify Moderator

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.

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