AC compressor cycle: 7s on 12s off

[JHZR2]

My 98 S10 ZR2 has a compressor cycle as 7s on, 12s off. It has cycled on and off continuously since new (and it has never been a once a minute type cycle). Is this too often? I have heard that sometimes a sign of a low charge is a cycle that is too frequent.

Ive never timed the cycle before, and the system doesnt have a sightglass.

So is this cycle too often?

Thanks,

JMH

 

[Chris142]

Yes a low charge will cause it to cycle. So will a very cold day. Turn the blower on high and see if it keeps cycling as much.

 

[JHZR2]

cold=lower pressure... makes sense.

Thing is, its cycled quickly since new. Wont a blower on high cause it to cycle more frequently?

Is there anything wrong with it cycling often? Maybe its done to make it more efficient?

Air has always blown ice cold... Still does. Its only a very small volume though (regular cab pickup).

JMH

 

[tdi-rick]

fan on high increases the load on the evaporator, so should increase the run cycle.
Also check to make sure that nothing is obstructing the return air. Plastic bags, etc. have been known to have been sucked into and block the return air.
Is there a filter in the sysytem ?
If so, check and clean it.

 

[tblazed]

On my 2002 Trailblazer, the compressor cycles about like you describe. I was told it is normal for a scroll-type compressor. Possibly your S-10 has that type too. Normally I would have thought the refrigerant was low, or it had a part-clogged orifice causing excessive cycling. Took it in to get checked out while still in warranty, got an update done to the controller which had no effect on the frequency of the cycling, and compared it to a friends Trailblazer which cycles like mine does. Researching it, I found a warranty failure of 1.35 per 1000 of these (.135%), so I concluded the frequent cycling is normal, an effort to get more mpg and efficiency, and won't cause early failure or damage. Blows 42° air when the ambient temp is 95° or so, so it definitely works, and cools.

 

[kenw]

Scroll compressor? In a car?

the cycle time seems ok. 42 isn't very cold tho, I usually look for mid-lo 30s at max fan and recirculate. It should not change much with engine RPM. If it does, that's a sure sign of low freon.

 

[JHZR2]

I was just talking to someon who said thatr scroll compresors are finding their way more and more into AC systems...

JMH

 

[XS650]

My 95 S15 has cycled fairly frewuently since new 106,000 miles ago. Except for three low pressure switches and needing freon about every 3 years, it's doing fine. The cycling doen't seem to have caused the clutch or related parts any problems.

 

[JHZR2]

wow, youve needed freon every 3 years? Mine is still day 1 cold, and Ive never added any.

I assume in CA you use the AC all the time? Northern CA isnt desert or anything, but as I recall, it doent get that cold. Maybe Im way off though?

I run mine any time Im in any vehicle, I think it keeps the seals softer and better sealing. No issues, even in my 83 MB.

Good to know that there isnt any issue on the clutches, etc.

Thanks!

JMH

 

[XS650]

quote:

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Originally posted by JHZR2:
wow, youve needed freon every 3 years? Mine is still day 1 cold, and Ive never added any.

I assume in CA you use the AC all the time? Northern CA isnt desert or anything, but as I recall, it doent get that cold. Maybe Im way off though?


JMH

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I generally use it most of the time. For cool in the summer and dry air in the winter. Humidity sucks.

 

[tdi-rick]

quote:

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I was just talking to someon who said thatr scroll compresors are finding their way more and more into AC systems...

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Hmmm, I've been servicing scrolls in residential/commercial/industrial applications for years, and one of their idiosyncrasies is that they have a small sump, and when low on refrigerant, tend to foam and pump the remaining oil out of the compressor and into the system. The clearances are pretty tight, so you can guess what happens next........
Mobile systems tend to lose their gas a lot more frequently than a 'fixed' one, so......

 

[kc8adu]

quote:

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Originally posted by kenw:
Scroll compressor? In a car?

the cycle time seems ok. 42 isn't very cold tho, I usually look for mid-lo 30s at max fan and recirculate. It should not change much with engine RPM. If it does, that's a sure sign of low freon.

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i doubt you will see low 30's in a ac without evap icing.low 40's is good.i can get 39 on a 90 degree day in recirc after the cabin cools off.
this is in both a 88 g20 and 85 olds wagon both r12
i get 43 in the 70 elcamino.glad i saw the writing on the wall and hoarded r12 while cheap.

 

[kenw]

fwiw, we drove from Houston to San Marcos Texas this weekend and the Highlander was reading 38f at center vent, high fan, recirculate once thing settled down. Outside temps were mid-upper 90s. This is a factory r134a unit with no recharge since we bought it 2 years ago.

Over the last 2-3 weeks my Camry is running about 38f under the same conditions, but has been opened and recharged at least once times in it's lifetime. It is a factory r134a system.

Last weekend I drove my son's 93 Camry (r12) from College Sta, Tx to San Marcos and it consistently ran about 36f under similar conditions, but it also has heavy window tint. At 180+k miles, the entire system is still original and has never been opened but has seen an occassional recharge. I have 2 cans of r12 left......

So my mid-30s statement may have been a bit optimistic, upper 30s would seem to be more appropriate for max fan/recirculate on my r134a units at least. Altho it is not uncommon for the temp to drop a tiny bit more if the fan speed is reduced, it is quite difficult to read it to 1 degree at 70+ mph.....

But lower-mid 40s still seems a bit clammy to me.