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Old 08-06-2020, 12:53 PM   #1
JWSmed
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Default Another AC question 2007 VUE 3.5

2007 VUE 3.5 engine

AC has stopped cooling. After reading here, it seems like my first step was mistaken (you know what's coming). I purchased one of the refrigerant refill kits that has the low-side gauge.

The gauge indicated full (green zone) while AC compressor was on, and it showed over pressure (in the yellow zone) when AC switch is turned off.

We did take it to a shop this morning for a free inspection. The following is a quote from the work order:

"Perform the following:
*Test and record temparature
*Inspect components for visible leaks
*Gauge and record freon pressures
*Inspect hose fittings and compressor
*Run performance test

No visible leaks detected at this time.
Compressor is not engaging and pressures are off.
Currently blowing 70*.
Need to perform Freon evacuation and recharge to continue with A/C concern."

I have not scheduled the evacuation and refill. The service writer said that the tech would refill with the dye so they could further inspect for leaks, but that this may not fix the system.

Does this sound correct? What else should we be looking for?

For giggles, I checked again and the compressor clutch is indeed engaging when we turn on the AC switch and stopping when we turn it off. I checked multiple times.

I did reattach the cheap refill gauge I bought and noted that when the clutch is engaged, the system shows just over 35 (on the low side of full in the green zone). When the AC switch is turned off it reads just above 50 (perhaps about 52 - on the low side of the yellow zone).
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Old 08-06-2020, 01:45 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: Another AC question 2007 VUE 3.5

When you removed the low side service valve cap did you notice any signs of dye? GM included dye in every ac system since r134a was established back in '94 or so. GM dye is greenish yellow and easily seen with the naked eye inside service valves since some leakage occurs when disconnecting charging hoses whether at factory assembly or during diy/repair shop assessments using gauges. If you don't see dye in the low side valve, remove the high side valve cap. Dye was the best idea since refrigeration was invented. Dye glows with an inexpensive uv blacklight from most auto stores and the first thing I suggest before buying the refill kit.

Warning: Do not use any r134a refill with sealer. Anyone using sealer automatically inherits/assumes all damages from sealer usage. It not only seals a leak but also seals off passages in ac systems, contaminating the entire system. If a leak isn't sealed by sealer (most find it doesn't) then the most likely step is seeking out professional help. Once sealer is discovered in a system, the repair shops will quote outrageous (and justified) repair costs as the system would require disassembling to flush out sealer then determining what parts need to be replaced that may be damaged from sealer use. I'm a diyer from r12 days and never used sealer for any reason. With equipment to make home repairs equal to dealer/repair shops, I don't use sealer. They don't use sealer in repairs. Contamination and sealing in the wrong places is a result of diy attempts to save money every dealer and repair shop knows. More damage occurs with sealer use than painstakingly searching for the elusive leak with a uv light than reaching for refill kits containing sealer and deciding how to repair it.

The repair shop doesn't want you or anyone to know of dye used in GM ac systems since 1994 or around the time r12 systems were discontinued with r134a systems adding dye. Dye simply makes leak detecting easier for dealers, repair shops and diyers aware of it. An inexpensive uv light I bought found my first leak in my L300 a few years ago after 10 years of reliable ac. In less than 5 minutes, dye glowed and was traced to a machine crimp on one hose. In the dark, in a parking lot at Home Depot since I was shopping for something and decided to try it out the uv light. Leaks are 98% of almost every vehicle ac problem.

Your system leaked out refrigerant, period. Once you decide to attempt ac repairs you become the ac repairman with all the risks and steep learning curve if you continue. The least amount of money spent would be the uv light then deciding whether you can handle simple remove and replace of damaged parts and then continue with equipment to evacuate and recharge or leave this to the shops capable of this.
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Old 08-06-2020, 02:12 PM   #3
JWSmed
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Default Re: Another AC question 2007 VUE 3.5

Thanks, fdryer! No, I did not see any evidence of dye. I did try to vizualize some with a small black light that we have. As you'll also not, the shop indicated that they did not see any evidence of a leak. I did not ask whether they checked with a UV black light, or just visually. THe kit I purchased was just the low-side gauge. I purchased a separate bottle of r134a with no sealant or dye.

This is actually my daughter's car. I don't know if it makes a difference, but she had the timing belt changed in the summer of last year, along with pulleys and water pump. The loss of AC just started early this summer.

I do at least know not to add any refrigerant with sealant. I can't guarantee that she or my son-in-law didn't have any refrigerant/sealant added in the last year or two, although I highly doubt it. My daughter does not remember ever having anything done to the car other than oil changes, tires and the timing belt service. My SIL is not a DIY type, so we highly certain that he did not do anything to it in the past.

I did see another thread, where I believe it may have been you, responded that the pressures should be checked and adding refrigerant should be done with the engine rev'd to at least 2000 RPM. Is that correct?

I did just go have my daughter rev the engine to 2000 and the low-side pressure reading dropped really low. I think this lines up with what you say about a leak. It's baffling that neither I nor the shop we took it to this AM haven't seen any dye or evidence of leakage.

Does the procedure that the shop said they would do next sound right to you? Evacuate the system and recharge with new 134a and dye to further check for leaks? The cost for that is about $150.
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Old 08-06-2020, 07:37 PM   #4
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Default Re: Another AC question 2007 VUE 3.5

Please remember that I am not a professional in vehicle ac repairs, am not sponsored or paid for my comments in these forums. As another diyer learning on my own and practicing on every ac repair, gaining experience does allow some perspective to make comments in these forums. I do not belong to other forums and have searched for expertise online. Only one site staffed with pros answers questions from anyone, free. Ackits.com. I compare what I know against pros answering questions from diyers that want expert answers on technical issues about vehicle ac systems. I liken myself to holding a bar (the ac forum) to measure my skills against them if I'm missing any nuances in ac diagnosing, troubleshooting and repairs. I'm not 100% knowledgeable and always welcome learning to add to knowledge.

Personally, I'm certain (99.99%) dye is in your system. Since almost all refrigerant leaked out, until you buy and use a uv light, you have no way to determine how the leak occurred or where it escaped. Every ac system in the world is 'sealed' once its assembled and operating. This applies to large commercial hvac units used in every building, home central air, window ac units, refrigerators and freezers. Refrigeration is the same whether its a walk in freezer to vehicle ac. The specific temperature is governed by whatever device is used to control temperatures. In Saturns and specifically Vues, a scroll type compressor and thermal expansion valve combines to mobulate refrigerant across the broad rpm band. Varying engine rpm also means varying compressor rpm. All stand alone refrigeration run at one motor rpm. Vehicle ac systems varying compressor rpm also means varying compressor pressures. this complicates understanding the varying pressures to anyone unfamiliar with vehicle ac pressures. Your observation of raising rpm and noticing the low side drop dramatically to well below guidelines is another indication of a loss of refrigerant from.........a leak. Fortunately, not using any sealer allows you to find the leak with a uv light without second guessing. Under normal operating conditions (baseline info), every Saturn vehicle will show low side pressures not deviating from 28-35 psi while high side pressures vary from 125-250+ psi when engine rpm varies.

Vue service manuals do not specify raising engine rpm to 2k rpm as the scroll compressor and its scroll control valve maintains an even pressure differential between idle to high rpm. The S-series and L-series requires 2k rpm because both use variable displacement compressors operating differently from your scroll compressor. The fact that you searched and used 2k rpm just to see if pressures change already makes you aware of how things are different. A normal system will not vary pressures within a range as mentioned above in Vues. In my L300, pressures will vary and misleading if idle rpm is used when 2k rpm is the recommended value to monitor pressures. No harm done but seeing a very different low side pressure is already informing you of what you aren't aware of.

To state the repair shop wants to remove any remaining refrigerant, evacuate then refill before making any leak test is disingenuous. I assure you, based on just your careful observations, that a leak released refrigerant. The leak may simply be one or both service valves with a loosely screwed on caps that provides primary sealing to the two schrader valves. A leak is a leak no matter if its a large rupture, tiny pinhole, worn shaft seal or loose fitting. Invisible refrigerant, oil and dye leaves a system with oil and dye marking the leak site. While its difficult to prove a worn service valve seal with gauges connected, this is only one reason to bypass repair shops and refill (carefully) with r134a (sans sealer) to an appropriate level when operating pressures fall within the range specified in service manuals. The use of low cost single gauge to inject refrigerant into the low side has its own issues as you do not know when to stop unless very careful of refilling a few ounces at a time. By injecting few ounces then stopping and observing pressure, you must observe center vent temperatures as the system needs a few minutes to stabilize. In your Vue, idle rpm is recommended to follow service manual guidelines. Increasing idle rpm while injecting refrigerant simply allows more refrigerant into the system as compressor speed draws in fresh refrigerant in a nearly empty system. Nearly as in the compressor still runs. At a certain level below 40 psi on the high side, the system pressure sensor detects too much loss of refrigerant and sends a disable signal to the engine computer to disable power to the compressor. This indicates, to me, something between a quarter to half the amount of refrigerant remains, too low to provide cooling but enough to allow compressor operation with zero cooling. As I mentioned previously, you're in a steep learning curve. I'm describing refrigeration as its occurring with your observations.

It's your choice to a)try spending time with a uv light to search for the elusive leak, b)simply add refrigerant on your own and take a calculated risk to determine where the leak occurred or c)try the repair shop with zero guarantee of saving money as they know a leak occurred that (in my personal opinion) is not a way to determine where the leak occurred as you're paying them to refill a leaking system. My choice is personal, spending the least amount of money on a uv light that can be used on any vehicle with dye already added at factory assembly. I don't waste refrigerant at all this way.

By the way, evacuating any system should be followed immediately with observing both refrigeration gauges to determine any leak since a leak means the system cannot hold a vacuum. If a leak cannot hold a vacuum, there's no point in refilling a system presumed to have dye already in it. This goes against epa regulations of refilling a leaking system (with additional dye) and letting it leak, going against releasing refrigerant into the atmosphere. And in addition, leak testing cannot reveal service valve leaks since both gauges are connected. Refilling with or without dye requires both gauges connected then disconnecting gauges to allow the service valves to close and anticipate one or both valves leaking. You can do this on your own at less cost since you already have one gauge and one can of r134a.

Last edited by fdryer; 08-06-2020 at 07:44 PM.
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