A/C compressor starts even if switched off?

[Vista Cruiser 69]

Hi Guys,

my 2001 Tahoe dual AC has a leaking AC system. It works for about a month and then needs refill. So far so good, its winter now and will check leaks in a couple of months....
By now the system should be quite empty. And even if switched off, the compressor starts about every 40 seconds and decouples after 5 seconds again. No sounds at idle, but when driving I was confused by a squeak every 40 seconds or so because the belt slipped when compressor switched on - quite annoying.

Helped myself by tearing off the plug from the AC compressor - silent now - but what makes me wonder is why at all that thing starte every 40 seconds when
a) being empty
b) swittched off?

Thanks for some thoughts!

 

[MO Viet Vet]

Sounds like the low pressure clutch cycling switch. It is at the accumulator. You can unplug it instead of the compressor if you want. It threads on at the accumulator with an o-ring seal. The shrader valve at that threaded stem may be loose or bad causing your leak. Get a new switch and shrader valve from Rock Auto-get AC Delco parts or get at your local parts store and replace. The shrader valve threads out and in just like a shrader valve at a tire valve stem but the tool is different-slightly bigger.

 

[Vista Cruiser 69]

Thanks, raiderron.
Was tough to get my fingers through to the compressor to pull the plug - next time I will do on the accumulator.
So actually the system is meant to engage the compressor frequently (every 4o seconds or so) at low pressure - even if switched off at the dashboard? Any idea why this should happen? I just do not understand the sense in it.
If AC was switched on, then, yes, but all AC systems I know won't start the compressor when switched off and as well not if system was empty...

 

[MO Viet Vet]

Sorry for the confusion. The a/c system will cycle the clutch when the a/c is turned on and will also cycle if the defroster is turned on. The cycling while the defroster is on is to help remove moisture in the air in the cabin of vehicle. It will not blow cold, the defroster should blow the temp you set, but the compressor is used to help with the moisture content that adds to the fog inside the windshield. I believe the switch at the accumulator has shorted and if the system is cycling in any other mode it is an inexpensive repair and the switch is known to have problems. Recommend AC Delco switch replacement.

 

[Vista Cruiser 69]

Hi,

now a couple of days after pulling off the plug to stop this squeeking AC on off I sense a lower fuel consumption - which makes sense. I always struggle to convert our European Liters/100km to your mpg but it is near 10% lower. Quit some level of confidence on this as my (say my wife's) fuel consumption is quite flat. That constant on and off compressor seems to make a difference.

 

[MO Viet Vet]

Yes, over time it would make a difference in fuel consumption. Anytime the compressor is on there is more drag on the engine and more fuel used. Less noticeable at highway speeds.