Automotive Air Conditioning Information Forum (Archives)

a94civicex on Mon July 15, 2013 11:32 AM

Year: 1999
Make: chevrolet
Model: corvette
Refrigerant Type: r134
Pressure Low: 0
Pressure High: 0
Country of Origin: United States

Year: 1999, A/C: manual
Problem: A/C not blowing cold
I vacuumed (had negative pressure for 24 hrs), added dye and recharged the system. The system blew cold for about a week (no compressor noise). I checked for leaks and found traces of dye under the compressor and on it.
Question: If the compressor had a leak could a negative pressure be maintained??
If I change the compressor,orifice and dryer should I flush the entire system??
Thanks for any help

mk378 on Mon July 15, 2013 12:19 PM

Yes there are leaks that hold vacuum but not pressure. The compressor you have is prone to leak like that at the case joints. Generally flushing is done in case of a blown / siezed compressor, it's not necessary for simple leak repairs.

GM Tech on Mon July 15, 2013 1:27 PM

I never flush for failure mode of a leak........

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The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

iceman2555 on Mon July 15, 2013 9:00 PM

Always back up a dye test with a good leak detector. It is possible for dye to be present and the unit not leak. Esp r4 and the case seals. Get these back....return tag indicates a case seal leak and after testing....opps no leaks. We utilize two type of test for leaks....a standard charge the compressor with gas (135 psi case) and submerge in a alcohol/water test tank. Second is a mass spectrometer test. Same internal compressor case pressure, however, the compressor is inside a vacuum chamber. No leakee here...no leakee there....
The reason dye is present and not refrigerant is the migration of lubricant on the oring during operation of the unit.
Check your Schrader vales and other seals for a possible leak. Got dye dripping on the engine block....different story.....probably pick up the leak with a leak detector also.
Good luck

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

GM Tech on Tue July 16, 2013 12:30 AM

I used to do those tests..I;m here to say that if there is dye present there has been a leak at some point in time. how else did it get there??

I set up a heat lamp on compressors that have the real stuff 134a in them- then I'd monitor pressure automatically turning off the lamp at 400 psi and back on again at 100 psi.let it cycle 5 or 6 times a day-up to 400 lamp off -down to 100 psi-- lamp on and I had one particular R-4 that leaked at exactly 231 psi as it went up in pressure and as it went down..it when actually squeaked like letting air out of a balloon (squeazing the neck) at 231 psi.

So I now believe that dye is better than any leak test- it tells you where and if there is a leak- just not when--- how can one test a compressor at every pressure point- and who decides what pressure to use for the test? when it can vary all over the place?

My test lamp was actually shattered by a "Non-leaker" that sprayed refrigerant onto it at a given pressure-so O-rings can leak at various pressure- and if it tests good at your 150 test pressure- it means it doesn't leak at 150- but maybe at 147psi..

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

Leggie on Tue July 16, 2013 1:50 PM

Quote
Originally posted by: a94civicex
Year: 1999, A/C: manual

Problem: A/C not blowing cold

I vacuumed (had negative pressure for 24 hrs), added dye and recharged the system. The system blew cold for about a week (no compressor noise). I checked for leaks and found traces of dye under the compressor and on it.

Question: If the compressor had a leak could a negative pressure be maintained??

If I change the compressor,orifice and dryer should I flush the entire system??

Thanks for any help

Negative pressure only applies -14.6 lbs differential at the most.
Did you check for leaks at service ports? These can be evasive, because your gauges keep them covered while it is getting serviced so they go undetected often times.

When you replace the compressor, drain the oil into a pre-tared bowl. Weigh it. If there's solid matters in it, definitely flush and add an inline filter before the orifice tube. If not, you can do more harm by flushing.

Drain the new compressor completely as well, then put back in about 1/2 to 1oz more than the amount of oil that came out of old compressor to make up for loss in replacing the dryer.

iceman2555 on Tue July 16, 2013 6:33 PM

After the military begin to add AC to the Hummers used in the Middle East several problems begin to surface. One was the dye present at the O Ring seals on the outer case, between the steel band and the aluminum case. The idea was that the systems were leaking refrigerant at this point....how else could this happen if refrigerant was not being displaced at this location.

There is no information concerning the amount of refrigerant recovered with these failures...the military does not always recover and recycle....esp over there....be surprised what chemicals we discover being utilized in some of these system. Nor was the supplied information indicating that the systems were not performing....just that dye was evident and therefore....it was leaking. Many of these units were returned for evaluation and test stand testing. These units were subjected to strenuous testing, pressure/pump up, vacuum, leaks, mass spectrometer, and both 500 and 300 hr durability testing. A great majority of the units tested passed all test without issues. Some failed either leaks or mechanical failures, but less than .87% indicated pressure leaks at the point of dye expulsion.

Also the heat conditions in Iraq are tremendous and the majority of these vehicles operate 24/7....very rarely shut down.
As part of this evaluation several of the staff accompanied the military to the deserts of CA for field evaluation during training manuvers to determine is actual operational conditions could result in a condition that we were not experiencing in the shop. Once more....not a major issue with gut pack/case seal leaks.

Understand that these units do come thru and yes, some of the units exhibit leakage in this area....however, the majority do not. Dye is present....refrigerant leakage is not. We do also test with 134a on certain occasions. For this reason, we always back up a dye test with a leak detector. Two different leak detectors are available for use, both are infrared units, a Fieldpiece SRL2K7 and a Robinair 22791. Both have proven to be very dependable units. Normally when there is evidence of refrigerant leaks at this point, the failure is traced to 'feathering' of the seal itself or surfaces that are not finished and or rough.

The movement of the oring in the case as it rotates with case expansion and contraction tends to migrate lubricant around the seal. If there is oil on the oring at this time, the dye maybe be indicated.

Remember that dye moves with lubricant and not refrigerant. We has also seen this same example with the famous belly leakers, both the HT and V5/7 variations.

Heating the compressor with a heat lamp could increase the case band (steel ring) temperature so that the temperature of the ring could result in expansion of the band. This could result in a break of oring tension and a resultant leak. Do you have a actual temperature of the compressor case during this test? Would like to know this and we could run a test on the stand and attempt to mimic this condition.

Also, it was stated that this leak occurred with one unit...is this correct or was this over several units?

Testing of a unit for OE supply requires certain test standards. Compressors (R4) are tested to 180/200 psi actual compressor discharge port pressures. Batch testing is also completed and this pressure is elevated to 400 PSI. This far exceeds the 'normal' compressor operational discharge pressures. There are two test stand operations for OE supply, one a 500 hr durability test and the other is a 300 high stress test...max compressor rotation....high evap air inlet temps....elevated condenser temperatures...actually almost not condenser cooling....run till it breaks...or when the time limit is reached. The 300 hr test far surpasses any condition that would be experienced in a typical automotive operation in its lifetime. Looking at past test reports, there is not indication of serious case oring integrity failure during these test.

Later this year, when I return to Dallas, I shall attempt to locate returns that indicate a case leak. We shall test to determine if the leaks are refrigerant based or simply migration of lubricant due to case expansion. This should occur in August or September.


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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

GM Tech on Tue July 16, 2013 11:01 PM

Iceman- sounds like you dealt with the Hummers with the GM engines-I was in the Cincinnati plant on consultations that puts on the compressors and does the armor armor plating installs- windows etc- as well as the compressor- I was Delphi Thermal's field and product engineer and sat down those folks discussing best ways to leak in Iraq-- I was always afraid they'd want me to go there....

-------------------------
The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

iceman2555 on Wed July 17, 2013 5:09 PM

We also encountered problems in Afghanistan with some of the Ford products. One of the major private security forces there began to experience severe compressor failures with the FS10 and wanted to convert their vehicles to the Zexel/Tama units. They did ask for me to be able to travel there for instructions for the mechanics....pay was great....company refused....sure am glad.....already spend my days as a youth with the sound of bullets zooming past my head....and trying to borrow into the ground....or perhaps a freshly fertilized rice paddy....nope....not enough hazardous pay for that...not any more....beside....at my age and size....oh...well...let's simply leave it at that.

One of the major problems encountered with the Afghan group was the refrigerant that was being utilized.....actually....be more adapt at what ever refrigerant was available and could be used at the time of repair.

Have a friend that contracts with the gov't for repairs/rebuild for battle/worn/damaged vehicles returned to the US. Last year had one shipment with several hundred units that were all contaminated with R40. Serious stuff....very dangerous stuff....and we think we have problems here with Freeze 12. Boggles the mind.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson