A/C compressor cycling fast

StreetRanger01 · Jun 12, 2008

My a/c compressor seems to be cycling very quickly. It kicks on for about 5-10 seconds and then turns off for about the same amount of times. The air blows cold and seems fine but this cycling seems a little abnormal to me. I just don't want to ignore it and it be an issue so I figured I'd post and see what ya'll thought.

MAKG · Jun 13, 2008

If it's cold, don't worry about it. Cycle time is a function of ambient and inside temperature, and under some circumstances it can be that short. That on and off times are equal is good.

If you're really worried about it, inspect the system for oily deposits -- that's a sign of a leak.

But for A/C systems, as for just about anything else, if it ain't broke, don't fix it.

92MiniMonster · Jun 15, 2008

IMO, it needs more r-134, its ok that it is on for the same amount of time it is off, i guess. But when at idle with the truck parked, the compressor should stay on always. If the compressor is off more than it is on, the truck will never go cold. It does have to do with temperature, but, i know for certain the compressor should stay on all the time when parked at idle.

fixizin · Jun 16, 2008

What if it's off LESS than it's on, and still plenty cold? Is that just the start of the problem?

What is there to know about recharging it yourself with a can of r-134 from Guido's Auto Parts?

MAKG · Jun 16, 2008

If it's cold and quiet, it's fine.

If it ain't broke, don't fix it.

92MiniMonster · Jun 16, 2008

If its cold, i guess roll with it. Although ive never had anything that was cold if its off more than on. You must have a kick ass compressor. There isnt much to know, i go with the basics, the guage that comes with the adapter recharge kit is very accurate. You want to hook up the guage/can on the dryer, and with the truck running in park and the a/c on, while the compressor is running the guage should be between 25 and 45 psi. Thats the main thing, its a must that you read that psi while the compressor is clicked on. And once you have that, the compressor should do like i stated in my last post.

fixizin · Jun 16, 2008

Mine is ON more than it's off, but still, after NINE years, I figure it needs a booster shot, eh?

I'll roll with it for a while... this is the acid-test time of year... strongest sun in the continental US... straight overhead at solar noon... no aftermarket tinting.

MAKG · Jun 17, 2008

The hardest weather on an air conditioner is DRY hot air. It's not Florida. It's Nevada.

I have a 13 year old air conditioner on the Prizm. It's just fine. It's never been opened (though it has had a set of gauges on it).

For the third time in this thread, if it ain't broke, don't fix it.

StreetRanger01 · Jun 17, 2008

Thanks for the input fellas. I think I'm going to take the original advice for now and let it be unless it stops blowing cold.

fixizin · Jun 17, 2008

MAKG said:
The hardest weather on an air conditioner is DRY hot air. It's not Florida. It's Nevada.

How do you figure? Takes more heat exchange to cool HUMID air. (Not to mention dumping/draining all that condensate.) But the truck's lived in NV and AZ too.

For the third time in this thread, if it ain't broke, don't fix it.

But, but... won't the cycling degrade my clutch... and my MPGs, from PCM having to jink around?

MAKG · Jun 17, 2008

It's true that the air conditioner affects idle. But if you're idling, your mileage is zero.

The effect of clutching and unclutching on highway driving is utterly negligible. Especially when you compare it to the effects of screwing up on an A/C repair. And just how much fuel do you think it takes to run an air conditioner? Hint: you can IDLE the vehicle with it running.

Dry air makes for substantially less effective heat transfer at the condenser. This makes it run hotter, and hence at higher pressure.

And the hottest part of Nevada is hotter than the hottest part of Florida. By a lot (Vegas routinely approaches 120 deg in summer).

StreetRanger01 · Jun 17, 2008

I put a gauge on it today (one of those ones from the store with the bottle) and it read in the normal range at about 30 psi. So it must be fine, although someone did mention something about some switch to me that controls it. Could this switch be an issue or no?

gw33gp · Jun 18, 2008

MAKG said:
Dry air makes for substantially less effective heat transfer at the condenser. This makes it run hotter, and hence at higher pressure.

I use to think the same thing because it seems to make sense. However, at the track with my race car I find the engine runs hotter with higher humidity and high temperature than it does with with low humidity and high temperature. I find this to be consistent after many years of racing in So. Cal.

Do you have any data or reports that supports the dry air vs hot air cooling effect on a radiator or condenser? If you do I would like a reference because I would like to figure out why I am experiencing the opposite and don't understand why.

TrexMex · Jun 18, 2008

StreetRanger01 said:
My a/c compressor seems to be cycling very quickly. It kicks on for about 5-10 seconds and then turns off for about the same amount of times. The air blows cold and seems fine but this cycling seems a little abnormal to me. I just don't want to ignore it and it be an issue so I figured I'd post and see what ya'll thought.

Besides all the discussion going on about dry vs humid air (Humidity DEFINETLY helps, BTW, as the heat transfer capability of water is much higher than air by itself) I think I have the solution for the original question....

I had the exact same problem months ago, there is a pressure cycling switch that goes bad and makes the compressor clutch go on and off.... Yes I read the if it ain't broken why fix it thing a ton of times on this thread but then again why put the fan clutch under unnecessary stress? My bet is replace that switch and your problem will go away.

fixizin · Jun 18, 2008

That's what I'm thinking too, i.e. that the pressure sensing switch would be designed to fail-safe in the direction of triggering early, rather than late or not at all.

So Trex, how much $$ for the switch? Oh crap, bet you gotta de-pump the whole system, right?

I wanna take MAKG's advice, but then again we're guys, so we all have to overcome the urge to "mess with it", eh? :derisive:

Additionally, I have manual tranny, so even at boulevard speeds (45mph) I can FEEL it cycling via "the seat of my pants"... this triggers the Sgt. Schultz voice in my head... "zer izz ZUMthing wr-r-r-rong wiss zee mechaNISM!"

A/C compressor cycling fast

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