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A/C diagnostic help please

A/C diagnostic help please

Postby VDWtrucks [OP] » Jun 29 2020, 3:06am

Any assistance you can provide I would appreciate.

I have a 2004 GMC Sierra with a 5.3L and 108k miles. I had the A/C serviced last year and they replaced the low side shrader valve, evacuated, recharged, and replaced the engine cooling fan clutch. When i drove away i can't say it was ice cold but the truck is older so i figured maybe this is as good as it will get. By the end of the summer it was warm air blowing and now it will not even engage.

So I like to repair things myself if possible as I get a lot of gratification. Watched a lot of videos and read numerous things on the internet. I got a set of manifold gauges and hooked them up. Static pressure this evening was 10 PSI on both sides with an outside temp of 85ish. At 10 PSI is there really any refrigerant in the system?

With the truck running and using a jump wire to engage the compressor i got readings of -10 PSI low side and 55 PSI high side. Maybe these readings tell me nothing but wanted to ask. I obviously have some kind of leak but it is strange it passed the test last year (or at least it comes across that way) and in a short period of time has become inoperable again.

I don't have a black light but could visibly see some dye around the high side valve. My thought was that was leaking now after having equipment hooked up as it was not replaced last year. Could i have really lost all refrigerant out of the high side valve or do i likely have a much bigger problem?

Thanks for your time!!
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Re: A/C diagnostic help please

Postby chem_man » Jun 29 2020, 7:38am

First off, congrats for purchasing a manifold gauge set!

The short answer to your question is yes, the R134a could have leaked out of a high side fitting if it wasn't sealing properly. Just as an FYI, there are 2 kinds of high side fittings that I know about - the Schrader valve type and the ball type. I had problems last year with a ball type high side valve not sealing properly on our 1999 Buick Century and I found it after injecting uV dye into the system and looking at it with a uV light.

FYI, you can "rent" a uV dye based AC leak detection kit from AutoZone (that is what I did) and tracked the leak down to the ball in the high side fitting. I played with the fitting by putting the high side line of the manifold gauge set on and off of the the fitting about 10 times and it finally sealed properly, and when I check the pressures in the system about 10 days ago, they were the same as when I did the work on the system last summer and fixed that leak.

If you cannot get the high side fitting to seat and seal properly, replacement Schrader fittings are available at most auto parts stores (at least NAPA, Carquest and O'Reilly have them). Also, the ACDelco part number is 15-5438.

Good luck!
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Re: A/C diagnostic help please

Postby VDWtrucks [OP] » Jun 29 2020, 8:39pm

Thanks Chem man!

I am steering towards the high side valve since I could visibly see some green dye around it. I will check with Autozone regarding a leak detector.

That is the part number i have written down as a replacement for the high side valve. I do have the ball type.

As far as the gauges showing i have 10 PSI, do you think there is really anything in the system to evacuate?

Does the gauge readings i got when i forced the compressor to run mean anything. I am guessing not since the system is so low or empty for that matter.

Thanks guys!
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Re: A/C diagnostic help please

Postby freonpushr » Jun 29 2020, 9:08pm

In your post you said you had a -10 psi on the suction side while you were testing the system. There is a good chance with your refrigerant leak and running in a negative pressure, you could have induced some non condensables if the leak is not where you think it might be. I would evacuate the system before adding the refrigerant for your final charge, and weigh it in.
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Re: A/C diagnostic help please

Postby VDWtrucks [OP] » Jun 29 2020, 9:49pm

My plan is to definitely vacuum it down before refilling.

Last year when it was serviced I suspect they added a dye. How long could I possibly see the uv dye? Is there going to be a time limit as to how long it will be visible?
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Re: A/C diagnostic help please

Postby MIKE91B » Jun 29 2020, 10:18pm

Here are my thoughts. You will always have dye traces on the service ports. That’s due to the dye being injected. They all show this. Get a black light and find the hole. If it has dye in it and it leaked the entire charge off. It will be easy to find. In my experience if the valves are leaking it will dump the charge much faster than what you experienced. All I’m saying is use the black light before you buy parts.
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Re: A/C diagnostic help please

Postby EaOutlaw1969EaOutlaw1969 is online! » Jun 29 2020, 11:19pm

I agree unless you know for sure the high and low side service ports and caps were spotless when the truck was fixed last year the UV dye would be expected.
If you ask me they never found the leak last year which could be anything from a evaporator leak to a compressor leak and anything else in the system.
Do as Mike suggested look the entire system over with the light and glasses while you are in a dark environment to make spotting the leak that much easier.
I think it may be a leaking evaporator because the evaporator case gets filled with leaves and debris and normally does not dry out when not in use which leads to corrosion from the outside in. this would be hard to spot if it was a slow leak at the time which is why they put the dye in it the first place.
Yet a slow leak in the evaporator case is impossible to find with UV dye until it leaks out enough dye to stain the drain tube. ( so make sure to look at the ac drain )
Also any time the system is opened up or serviced make sure to replace the AC dryer and orifice tube pull a vacuum long enough to get rid of the moisture and set it to hold that vacuum if you lose vacuum you still have a leak. some argue how long the vacuum will hold if there is not leak. the problem with any answer is the ac gauges and connection points if they leak ( most cheap gauges and hose connections do leak ) you will never know if your system is fixed.
Most ac guys will tell you it needs to hold this vacuum for 15-30 minutes but I can say I have never ever had a come back on a ac job that held a vacuum for a solid hour or longer.
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Re: A/C diagnostic help please

Postby VDWtrucks [OP] » Jun 30 2020, 5:23am

Thank you guys for your input, I really appreciate it!

I will pick up a black light and begin my quest to find the leak. I will try to report back on my findings in the next few days.

Thanks!
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Re: A/C diagnostic help please

Postby VDWtrucks [OP] » Jul 01 2020, 3:27am

Picked up a uv light and looked over everything to the best of my abilities. Releaaed a bit if pressure from the low side and verified it has dye. Now the system hasn't actually ran for any extended period of time, since last year. I found nothing.

So what's your advice? Purchase more refrigerant with dye and do it again or go straight to the evaporator for replacement along with accumulator and orifice tube?
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Re: A/C diagnostic help please

Postby EaOutlaw1969EaOutlaw1969 is online! » Jul 01 2020, 8:59am

I would do my best to inspect every inch of the system before I purchased any parts, unless I knew my vehicle was old enough to warrant a shot gun approach to ac repairs and replace every major part in the system, AC compressor evaporator condenser hoses dryer orifice tube condenser fans.

A repair like this may seem crazy at first until you start to understand that each part of the AC system has oil in it when you loose refrigerant you lose oil. How much oil did you lose? how much to put back? A proper balance of oil is critical. worse of all your truck is older and may have had countless techs adding oil and dye laced refrigerant each time they charge it, who knows if they even put the right oil in the system.

Sure you can remove and flush the lines, remove the dryer and toss it remove the orifice tube ( providing the damn thing does not break ) remove and drain the compressor flush the evaporator and condenser add the correct amount of oil back into each one of the parts. then you know you have the proper amount of oil in the system and the oil is where it needs to be. ( yet all this work was done to parts that may be leaking or otherwise damaged anyways).

Short of doing this you may have to take stuff apart to find the leak. A lighted endoscope will help minimize how much you have to take apart.
I have used one in the past to find a evaporator leak on a F Ranger by removing the fan motor I could see just part of the evaporator. that inspection revealed lot of leaves and debris in the evaporator housing once I fished much of that out I was able to see the evaporator fins had corroded severely and had a oil stained appearance sure sign of a leak. the corroded fins and getting rid of the putrid smell of rotting leaves was enough incentive to replace that evaporator leaking or not.
The condenser on any vehicle is an easy target for rocks and debris sand and grass etc from the road to smash it to bits and clog up the fins. so if your ac parts are as old as the truck they are probably due to be replaced anyways. But there is no harm in removing it and capping off the lines and the inlet and outlet ports so you can inspect it on both sides very closely for damage from rocks or deteriorating fins from old age. any signs of oil at fittings or any part of the condenser warrants a closer inspection with a uv light in a dark environment ( by the way if you just have the light and not the glasses it will be harder to spot leaks ) if the condenser is in great shape now is the time to flush it inside and out yes back flush the fins getting dirt bugs etc out then inspect it with a flashlight and use a quality condenser comb to straighten out any bent fins . Yet these things are cheap enough they tend not to be worth the effort and chemicals required to get it properly cleaned.

If you need to keep it cheap and you feel you have inspected the vehicle as far as your willing or able then the only other thing to do is a vacuum test .
pull a vacuum and see how long it holds the correct amount of vacuum (this has to be done with a leak free and tested gauge set) if the system will not hold a vacuum you will have to get evasive and start removing parts until you find the wet oily spot.

Just remember when making a decision of what to do, go back to the time when the AC was just service and the so called leak was fixed, it did not cool properly did it ? was it from a under or over charging it with refrigerant? was it because of too much oil? was it because of a contaminated receiver dryer?
Was the lack of efficiency due to a plugged up orifice tube? if so where did this debris come from ( normally the compressor ) if the system never was able to pull a proper vacuum and moisture was left in the system what has that moisture done to the system did the oil become acidic?

There is a lot more to think about your ac system than just topping it off till it feels cool.

I will say even if your parts are old OEM original parts they will perform better if they are in good enough shape and serviced properly compared to buying cheap aftermarket parts that may bolt up but are inferior in every way.

Some aftermarket parts are great and will last a long time and perform as good if not better than the factory parts, what aftermarket brands those are today I wouldn't know.

A few questions you have to ask yourself , do you have to tools time and experience and budget to do this work, is the truck a keeper? can you live with the system performing worse than it did when it was serviced last if you just charge it?

What you do and how far you go with this is up to you and your conscience. a small evaporator leak can become a large leak quick if this happens when you or your family are in the truck you need to know about the chemical you and your loved ones will be breathing in.
R-12 was bad for you if you inhaled some while smoking R134A is just plain deadly and I really do not know how it was ever approved for use in such a confined space like a vehicle.

http://www.afrox.co.za/en/images/R134a_tcm266-27719.pdf
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