Should my air conditioner compressor run like this?

[natjwest]

In June of this year, I had an AC compressor lock up on me. I got it replaced while on a trip. Then about a month ago, the new one died on me, again on a trip, I got it replaced under warranty from Kragen. But I'm not sure if it should run like this, with the frequent stops and starts:

http://flickr.com/gp/natjwest/74sLw6

Maybe I've never noticed it before, maybe it's always been like this and it's no big deal, but I'm a little paranoid about AC problems now since it's all one serpentine belt. Is this the correct way for the AC compressor to run? Cycling like that?

Note that when this video was taken, the AC was NOT on via the button in the cab and no cold air was blowing. It seems to run like this all the time, whether the engine is warm or cold, but I'm not certain of that.

 

[Franko914]

The compressor can also cycle on/off as in the video if you have your system set to "defrost" (front windshield icon) with the AC button in either On or Off positions.

 

[THEFERMANATOR]

There was a TSB awhile back regarding the compressor cycling even though the A/C was off. It was the fan blower switch sending power to the compressor with the unit off IIRC.

 

[natjwest]

Thank you very much Frank, when I flip the switch from defrost to any other setting the cycling ceases. I'll make the vents the default position of the switch from now on. But is this a defect like fermanator says or completely benign?

 

[WarWagon]

Many modes will attempt to run the clutch. Specifically: Defrost and Recirculation air modes. They don't turn on the AC light. If you are not in these modes than you have a problem. If the fan is off, and that would be a eyebrow raiser, I would put it on low to see if rec or defrost is on then adjust the modes. You need to hunt down the TSB as suggested above.

How cold was it out when you did that video? Low fan and temps would allow the clutch to stay off that long after kick out. The time the compressor spent off is what I noticed as being long... But yes, the clutch cycling is the way the "Cycleing Clutch Orface Tube" CCOT systems work. Clutch kicks out to keep the evaporator above 32 degrees and not turning into a ice brick with no airflow.

 

[WarWagon]

Thank you very much Frank, when I flip the switch from defrost to any other setting the cycling ceases. I'll make the vents the default position of the switch from now on. But is this a defect like fermanator says or completely benign?

Never hurts to test a TSB.

Defrost, in fog banks...
It is useful to run the compressor in defrost to reduce moisture in the cabin. Most automakers do this; so it is Normal. Cold days have their limit as water freezes at 32 degrees so the clutch cycles a lot. After the air is cooled and some moisture removed by the AC the air passes over the heater core if you have selected some heat. This heat reduces the humidity even more and allows the windows to defrost and stay that way. Your breath will add plenty of fogging ability to windows... Useful, but, not AC required to defrost windows. AC will allow you to avoid oven temps in some conditions to keep the windows clear. Conditions like warm ocean coastal fogs...

It also keeps the AC seals lubed during the winter...

 

[THEFERMANATOR]

Thank you very much Frank, when I flip the switch from defrost to any other setting the cycling ceases. I'll make the vents the default position of the switch from now on. But is this a defect like fermanator says or completely benign?

The compressor is supposed to run whenever defrost is on. The TSB was in regards to the compressor running when everything was turned off.