Model: Grand Cherokee
Engine Size: 4.7L
Refrigerant Type: R-134a
Ambient Temp: 65
Pressure Low: 26
Pressure High: 170
Country of Origin: United States
I'm very new to AC systems but an experienced hobbyist/DIY mechanic.
My Grand Cherokee was blowing hot air out of the AC and I wanted to
try and fix it on my own. I ran the self test for the blend doors and the Passenger
side was fine, the drivers side had too much travel but I was pretty sure I
should be getting cold air at least from te passenger side.
I rented a manifold guage set, vacuum pump and UV LEak detection kit so
I was ready to go.
I put the manifold guages on the system with the engine off and measured
70 psi on both the high and low side.
I then started the car with AC on high and fan blowing on high. The compressor was
cycling on for about 2 secs and off for around 10. Watching the low side pressure
it would turn on at 40 psi and off when it got to 20.
I then shut it off and connected the vacuum pump. I was able to get the vacuum
down to -28 in hg but not to 30.
I let it sit for 1 hour and it held the vacuum.
I then started filling it with R-134. I connected a can to the yellow hose
and then pressed the release valve on th eguage to purge the air from the yellow line.
I then opened the low pressure valve and started filling. The compressor staqrted
staying on longer and now is on all the time.
I was trying to get the pressure to 50/200 but it would only go to 26/165.
Im pretty sure I overfilled it because I put 4 -12oz cans of R-134 in it and afterwards I discovered
it should only take 27oz.
So, what is the best way to get the proper amount of R-134?
Should I bleed it all off, draw and vacuum and start over, or can a bleed off a little at a time
and measure high side pressure to know when I have the right amount?
Using a recovery machine, take it all out. Then evacuate to full vacuum and recharge 27 oz by weight. Ordinarily the orifice tube should be checked while it is empty but it appears you have one that is built into the line and can't be non-destructively removed.
The 65F ambient temperature is too low to properly evaluate performance. I would expect low high sides and long off cycles. Pressures looked good considering the conditions. (You don't want to run with a 50 psi low side.) The suction line and accumulator should have been getting cold. If the line is cold but the vents are warm it's an air side problem in the dash.
Is there a technical reason why I can capture refrigerant in a can or purely legal?
Im trying to get a real answer.
Often times speed limits are lowered in certain areas solely to generate revenue. If this
refrigerant law is to generate revenue for the AC shops then I have an issue with that.
Im trying to understand why it is illegal to vent refrigerant because from what I read
R-134a is NOT ozone depleting and therefore the perception is the law doesn't increase
safety or protect the environment, the only thing it does is protect margins for AC shops.
Junk yards vent refrierant all the time when they remove compressors, condensors, etc...
Also, R-134a is not ozone depleting, so it seems the only reason for the law is to artificially
provide high margin work for AC shops.
Based on that, is there NO way to get the proper amount of refrigerant in the system without
taking it to an AC shop?
If the answer is no then I guess I will have to vent ALL of the refrigerant, pull a vacumm, and start
I have read many places that the only way to get the proper refrigerant is to weigh it and
only shops have the equipment to weigh the refrig. Im pretty sure I can just weigh the 12oz
can's before I fill and after and from there accomplish exactly the same thing as a shop would with
Im not trying to be argumentitive, but I also have the ability to think for myself and simply saying, its
illegal, doesn't satisfy my curiosity or reasoning.
It is a law
HFC's are greenhouse gasses. Spend some time on the EPA site and you will see what the junk yards are being fined for non-compliance.
No there is no method to insure a correct refrigerant charge without the use of the correct recharge equipment, this involves some method of adequately weighing exactly how much refrigerant is introduced into the vehicle.
The venting of refrigerant is an illegal act...if it were merely to add to AC shop coffers...there you would not have been able to purchase the damn small can at all. The use of small cans is a major contributor to refrigerant leakage. CA just introduced some extremely aggressive pricing for small cans of refrigerant. I, for one, shall be very glad when they are gone. It is impossible to properly recharge a system using small cans and guessing as to the amount of refrigerant is actually being added to the system. Pressures are not indicative of a properly charged system. A properly recharged system will produce certain operational pressures and temperatures...not the other way around.
If you wish to save some serious bucks...a suggestion would be to obtain the services of a good AC shop and have them service the system. Your method is going to produce only one solution...the spending of more cash for a new compressor....and on this vehicle a new condenser....and of course the other parts required to insure a correct repair....so take your pick !!!!
Undercharged systems are the major contributor for compressor failures...both OE units and aftermarket as well. It is necessary for a system to be charged within 1/2 to 1 oz of total system requirements to insure proper lubricant migration for the system. Under charge this system by as much as a couple of ounces and start saving your cash. You are simply not going to achieve this with small cans of refrigerant...no why.....no how.....
Perhaps you should try 'blowing' refrigerant into a small can.....lets..see ambient temp is 65....static pressure in your can with a minimal amount of refrigerant will be.....66.43 psi....your stated low side is 28 psi.....not sure...but it is very difficult to push '28' into 66.43...but what the heck...forget the legal issues....try it.....or if you really have a set....hook it to the....no...will not even go there....hate to see you loose your fingers or hand......why not simply send the cash....have your vehicle serviced properly...save the extra and have a system that functions as expected.
Of course, as stated...vent the stuff....evac and try once more.....one thing is for sure....I bet the results will not change very much......but then you will have spent more cash on refrigerant....opps....wasted more cash on refrigerant.....ahhh...almost forgot something...the boiling point of water at 28 in/hg is 101 degrees....so perhaps your vacuum is not as good as your think....residual moisture in the system will result in acid formulations.....leading to compressor lubricant failure.....thus a new compressor....which probably produced sufficient debris to contaminate your condenser.....oppps...more cash.....perhaps now one begins to understand why I charge the hourly rates I do...it is not WHAT I DO........but WHAT I KNOW HOW TO DO.....
GOOD LUCK !!!!
The current course is headed to disaster.....not a reliable system.
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.
The short answer to your question is, if I take it to a shop I don't learn how it works. If I do it myself I get to learn, even from mistakes. I personally can not put a price on knowledge therefore, any financial analysys ends up on the positive for me doing it myself.
I specifically bought this vehicle as a hobby. I do 100% of the mechanical work myself and have literally saved $1000's of dollars already.
I do not know what you charge, but I can buy one heck of alot of $15 cans of R-134 for the $1000 the shops around me want to repair an ac system.
I already have a brand new compressor, accumulator, o-ring kit etc... laying on the garage floor ready to install. I have less than $200 in all the parts. Additionally as far as I am concerned I have already fixed the original problem, the AC blows ice cold air where as three days ago it did not.
On other forums I have talked to people who at least claim, as yourself, to be a professional AC certified person and they have said they have succesfully charged and topped off systems for many years using only pressure gauges, ambient temperature and small cans.
Lastly, I don't know in what world you guys live in, but in my world I would much prefer the EPA be solving problems like massive oil spills in the Gulf rather than chasing a hobbyist mechanic releasing a few oz of R-134 in his garage on a weekend.
Let me know where you live and Ill move there. It seems so wonderful I would probably be happy to pay extra for AC service. We can't even swim in Lake Michigan anytime it rains because Milwaukee's sewage treatment system releases raw sewage, again I would much prefer the EPA worry about that.
You can get professional advice here, if you wish to listen. It will rarely include short cuts that can lead to an early system failure, or instructions that require breaking the law. It is preferred to fix it right and comply with regulation.
You can do as you please. But a site designed to provide auto a/c information is not going to suggest the release of refrigerants period.
Simple answer to the questions. Fix the leak if there is one. Pull a vacuum before charging. Charge back to the OEM specs. Charging by pressures can lead to so many other issues and a shorten life of the system.
Let me go about this another way.
1) Assuming I am starting with a system with no refrigerant and if each can is 12oz by weight and a system requires exactly 24oz can't I just put two cans in the system? Wouldn't this fill the system to the proper amount? and if the requirement is not an even increment of 12oz, can't I weigh the can before I start and as Im filling and therefore get extremely close to the exact amount?
2) what is the minimum amount of work I can have performed by a shop? is it possible to have them just evacuate the system? no pulling a vacuum or refilling. And since they get to keep the refrigerant shouldn't this at least be free if not them paying me for the refrig they get to keep and reuse?
That should accomplish my goal of learning to work on the system and satisfy the legal requirements of not releasing refrigerant.
24 ounces is 24 ounces.
A shop will charge you to reclaim refrigerant and normally keep it also. You have man hours, shop equipment, $4k for a R & R machine. Plus in our shop we run a test check purity of refrigerant also before it's even hooked to our equipment.
Some of the oil change chains offer to reclaim and / or charge R-134a. That is the only A/C thing they do. I wouldn't have them do anything to my car other than take refrigerant out, but it's hard to mess that up.
I didn't say you had to go to a shop, there's nothing stopping you from buying the proper tools and obtaining the knowledge necessary to do it yourself. As you noticed, that investment will pay for itself in just a few uses. For example buying a 30 lb cylinder of R-134a is less than half the price of buying the same amount in small cans (40 cans). You can buy a scale with that money and then be equipped to make an exact charge every time with no waste.
Edited: Wed May 04, 2011 at 11:26 AM by mk378
With equipment to perform such tasks. If it does not pass the purity level. We say we can't work on your vehicle. Take it back top whomever put the contaminated refrigerant in your system. If it has a sealer in it depending on type. The customer is inform by opening the system every component could be damaged and need a replacement. You need to be able to weight 24 ounces. As I stated the equipment to reclaim refrigerant is 4K US. Refrigerant I identifier is 1K and a sealer analyzer is about $200.00.
Where have I said you need an expensive piece of equipment to weight something?
Any "experienced hobbyist/DIY mechanic" should have a great understanding on what they are working on. I believe you can benefit greatly from purchasing the AUTO AC REPAIR MANUAL that goes into detail on the auto a/c systems and understanding the functions for each component and how to test/repair/diagnose your own system, along with many different tools professionals use. Understanding the A/C system will make you understand the answers people are giving you.
Thanks because using 12 ounce cans can lead to not getting all of the refrigerant out of the can. So did you get 11.5 or 11.9 or of the can?
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