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A/C Gauge Reading For Your Analysis

I’m just relating things based on my personal experience. I know that if I see the high side gauge heading towards 300 PSI even on a 100 degree day I’m going to start getting antsy.
Since most of the A/C service work I’ve done is here in OK, and it does get pretty hot here with high 90s and low 100s common, I can only say that most of the systems I’ve worked with would run about 225 to 250 on a very hot day.

There have been a few (134 conversions usually) in which the high side would exceed 275 but at that point I stopped and did not pass GO. Changes were made to the orifice tubes, etc. and this brought the pressures down to a more manageable 230 give or take some.

Yes, I do think it needs a bit more of a charge; at least to bring it up to 225ish.
(Odd thing about my oldest son’s 96 Camaro. The factory fender tag on that car specifies less than one pound total refrigerant charge. How weird is that. If I ever have to go into the A/C on that car I guess I’ll find out how accurate that tag is.)

I was looking at the Chevy shop manual this morning and found some interesting stuff:

1.) The A/C System Performance Test table says that with an ambient temp of 75 degrees, the STATIC pressure should be 70 PSI. I didn’t record a STATIC PSI for the Impala AFTER charging, but I did for the Taurus and it was 78-79 after charging the first can (or very near ambient). I’m going to check the Impala again. I’m guessing it’s going to be in the proper range.

2.) The A/C Performance Table (Temperature based) says that at ambient temp of 76-85 degrees F and Relative Humidity of 35-60% (my Weather Channel electronic indicated 47%, but I doubted it’s ambient temp, so who knows?), the Low Side should be 31-42 PSI and the high side between 148-195 PSI (with a maximum left center discharge air temp of 60.8 F). I think I’m in the ballpark of these numbers right now.

3.) The A/C System Pressure - Zone Classification graph seems to indicate that at a Low Side Pressure of less than 35 PSI and a High Side Pressure of about 200 PSI, I’m in Zone B on the graph - which leads to a Diagnostic chart with a LOT of steps and verbiage. Maybe I should try to plow through this to see where it leads me. The problem with these tables is, whenever I’ve tried to use them, I usually hit a dead end because I don’t have the proper equipment (eg: “hook up the Rotunda”, or whatever it’s called …)

So - I think what I’m going to do next is buy a couple of thermometers to measure the vent temps in the cars. The manual says to use TWO at the same time - measuring the left and right vents at the driver’s cluster while running the car at 2000 rpm for 5 minutes. I was thinking not only could I do that, but maybe I could stick one in each car for a short-term test to see what that might reveal. Then, maybe I’ll buy another can of refrigerant if that’s what the diagnostic table leads to (this time with the PAG oil - both cars use PAG according to the manuals).

One question though: The Taurus has a tach on the cluster, but the Impala doesn’t. Can I just use engine sound to approximate 2000 rpm on the Impala (by using the Taurus), or do I have to buy a tach. And then how does one person maintain 2000 rpm - by manually manipulating the throttle linkage under the hood?

Also ran across some verbiage in the Impala manual that mentioned the possibility of dye incompatability: “Not all of the R-134a dyes are compatible with PAG oil. Some dyes decrease the oil viscosity or may chemically react with the oil”. It also said, “GM passenger cars are now manufactured with flourescent dye installed in the A/C system …[use GM dye J41447] and follow the procedure for vehicles that do not already contain the dye”. Funny - this manual is for the 2002 Impala/Monte Carlo. You’d think they’d be able to give a definitive statement as to whether these cars have the dye already in them from the factory or not (instead of the generic statement that they undoubtedly cut/pasted into ALL the manuals).

I always use the “pan of hot water” when I charge a system. I don’t know who recommended the shake method for getting the freon out but as far as I know, it is NOT recommended. I have seen warnings against this but I can’t remember where I saw them.

I fill up a 2-3 quart sauce pan with hot tap water and set the can down in it vertically. That pretty much completely empties the can in a couple of minutes. You need a little patience here (something I don’t have a lot of, or so I’ve been told).

I do have a vent thermometer and in every system that is working, I get 40?F air from the vent, and that is with the factory charge. I usually don’t get that with a system that I’ve had to recharge, but I write that off to age and wear. After all, if it was perfect, then I wouldn’t have had to recharge it, would I?

I stand corrected on the “300psi tops” comment. With todays systems and 134a, that should be “250 psi tops” and 225 should work just fine…The low side is more dependent on how good a shape your compressor is in. A “crisp” compressor can suck it down to 20 psi which usually makes for low vent temperatures. You can buy an A/C vent thermometer for $10, a very handy tool…

Hero, you are going about it in the right way, slow and easy…Most of these guys have no gauge manifold set, they just dump a can in and see what happens without having a clue what they are doing…

Thank you Caddyman.

I picked up the vent thermometer on the way back from grocery shopping this morning (Yes - I do the grocery shopping … with a grocery list on an Excel spreadsheet! It has the the product name, manufacturer, aisle location, best observed price, typical price, plus other stuff.). See Caddyman, you didn’t have any idea who you were talking to (LOL!).

Anyway, the thermometer indicated the following:

The Taurus was better than I thought. With the fan on HIGH and full cooling, the temperature read 48 degrees. As I got closer to home (a 15 minute ride), I turned down the fan a notch at a time and the temp dropped as low as 42! It felt pretty good and I actually think it’s good enough for now.

The Impala wasn’t as good. It could only get to a little better than 50 degrees (48-49) - at a much slower rate than the Taurus - and it felt warmer than that.

So I picked up one more can of the same stuff I’d been using - the Quest 12 oz can with UV. I wanted a can with the PAG oil in it, but AutoZone only had ONE can and it contained 8+ oz of oil and only 3 oz. of refrigerant (a bad mix, I thought). I’ll tell ya - it’s A/C service season around here right now and AutoZone is just pathetic. Nothing in the aisles and only a small cart with pegboard right in front of the front desk. No stock of any kind. When I bought the tap valve it was the only one they had. When I bought the thermometer today, it was the only one they had. That’s bad management in my opinion…

The thermometer was $7.99, by the way. It’s the manual dial gauge.

So - the next thing I’ll do is try to run through the diagnostic table in the Impala’s shop manual. If that leads to another charging, I’ll use keith’s 2-3 Qt sauce pan method. As far as the can-shaking method … that’s what was written on the can (“shake continuously while turning between 12 and 3 o’clock every 2-3 seconds”). I ran this by a chemical engineer at work and it made sense to him, but so did the warm bath method.

I agree with Caddyman about some of these people doing their own recharges. They head to AZ, buy a can of refrigerant with a charging hose attached, and then start asking questions about where to connect the hose at, etc. This is pretty shaky ground.

That rotating the can back and forth is an exercise in futility in my opinion. There is space in that can and when the can is upright liquid will be at the bottom and gas at the top. Rotating it will still leave gas at the top.
On occasion I flip a can upside down to speed the process up. This adds liquid to the system but I’ve also done enough of it that I’m not worried about blowing the valves out of a compressor.

It does sound like the Impala needs a bit more help, refrigerant-wise.

The AutoZone here has gone to hxxx in a handbasket and I seldom ever go in there anymore.
About 5 years ago they had a number of older gentlemen who had some mechanical expertise and they were on top of things. All of them are gone now and have been replaced by guys whose age makes them look like they’re skipping sophomore English classes at the high school. Rather than try to explain my way through things I just skip the store entirely unless it’s an absolute emergency.

Forgot to add. if the can isn’t getting ice cold, I think you may not have either punctured the can enough or did not back out the puncture valve enough afterward. Screw it in all the way, then all the way out.

Keith - with what just happened, I seem to have developed a fear of screwing anything all the way anymore. Even my wife complained that I was … eh … well, never mind… (LOL)

Seriously, though - I’m sure I had the tap all the way in and all the way out, but I DO remember on the very first can that I had punctured it (all the way in), started agitating it, and was watching the gauges wondering why nothing was happening. It wasn’t for probably a couple minutes (maybe longer) that I realized I hadn’t backed the pin out to allow the refrigerant to flow! Had to laugh at that one! Then, on the 2nd can, I DID back the pin all the way out, but forgot to open the low-side valve on the gauge set!

I’m thinking the constant agitation kept the temperature more elevated somehow. I never really did allow the can to sit still for any length of time.

I was in AutoZone today, but forgot about that tool you recommended. What is it? Is it something to tighten down a loose or leaking service port?

When I moved here to the Carolinas (from New England) in '95, I developed a relationship with AutoZone because they had stores in New England where I came from. I always thought I’d be moving back and I wanted to keep any “LifeTime” warrantys I had started. Well, in the 15 years I’ve been here, Advance has opened a 3rd store 2 minutes from my house - AND - they’ve expanded into New England, so I now go to either store. My experience with AutoZone here is pretty much what you’ve mentioned: When I first got here, they had pretty good people it seemed. But the last 5-6 years, they’ve been changing personnel at an alarming rate! It seems every other time I go in there they’ve got a new Store Manager and half the clerks have changed over. I’m not sure the three Advance stores are much better, but their approach seems to be fewer bodies and more mature (mostly men in their 30’s and 40’s). One trend I’ve noticed with Advance Auto - they’re almost always more expensive than AutoZone (for the same item). However, their online sales seem to trump AutoZone. I’ve got one of those AutoZone “Rewards” cards which gives you $20 off a purchase after making (5) $20 (or more) purchases. It never works out to 20% off because you always spend more than $20 (although you should’ve seen how well I partioned up all the parts purchased for my intake manifold gasket job on my Impala). Advance, on the other hand, seems to routinely run 20% off online sales, and so this is where I bought a set of Wagner brake discs for my Taurus recently.

Last weekend I stopped into CarQuest to see what kind of gauge sets they sold (turned out nothing special) and I asked the guy how they stayed in business (they’re never open past 5pm weekdays and barely on Saturday). Turns out they have signed 3-year agreements with large accounts that keep them afloat. Might be a similar situation with NAPA as their stores never seem to be open when I need them, either.

So the chain stores service the DIY’er and I guess they figure they can get away with hiring people who know little about repairing automobiles. And I would bet the pay isn’t that great, either…

Didn’t touch either car today. Preoccupied with the possibility of buying a house … just not sure in which state …

Finally got to the Impala today. Here’s what I found:

1.) STATIC Pressures: Low = 79/80, High = 79/80. These numbers seemed to correlate to ambient temperature, which turned out to be debatable. The Weather Channel said it was 72 degrees here with 52% humidity. My WC electronic thermometer had numbers 10+ degrees higher (that thing must need calibration of some kind), and the vent thermometer read 80 degrees. I went with the 80 degree number.

2.) RUNNING PRESSURES: I ran the test THREE times, third time manually holding the linkage under the hood so I could see the gauges real-time (A/C full blast, driver’s window open 6", 2000 rpm (guesstimate, no tach) for 5 minutes). Each time I got the same result: Vent Temp = 60 degrees, Low = 31 (28-34 range), High = 150 (145-205 range).

According to the Shop Manual Table, assuming ambient of 80 degrees F and GT 60% Humidity, the numbers should be Low = 32-46 and High = 155-212 PSI.

So I charged a can in warm water while watching the gauges. The warm water idea was truly magical - the can discharged completely in about a minute+! After charging, the numbers were: Vent Temp = 42-43 F (pretty good!), Low = 33 (fairly steady now, no real range), 165-173 (very slow cycling). New STATIC pressure after charging = 66 PSI (both sides). Could STATIC = AMBIENT be an indication of a low charge??? Before charging, both cars’ STATICS were right at ambient. Conincidence?

So I’m inside the proper ranges now with the Impala, but maybe still on the low side. It could probably take another partial can, but I’m going to stop for now and see what happens. I’m thinking, so far, I’ve added about 1.5 cans (maybe less) to the Impala (or about 18 oz). Now I’ll just sit back and see how long it lasts (while looking for obvious leaks).

I’ve gotten where I deal mostly with one of the two O’Reillys stores here. Odd thing is that the store I deal with is staffed with professionals and they have pretty much anything needed; including a paint shop, machine shop, and a very well stocked hardware section. Go 3 miles away to the other one and all you get is arguments, ulcers, and a bad attitude.

A couple of years ago I bought a reman alt. from the bad store and my testing showed this alt. was no good. After taking it back to the store they took it to the back and then returned with the proclamation this alt. was good. Since I always do tests twice I took the alt. to the good store and they pronounced it bad.
Back to the bad store I go and after telling them what the other store had to say I started getting this deer in the lights look and after a bit of interrogation the counter guy kind of mumbled something under his breath.

Not being sure of what he said, I sarcastically asked him if he mumbled something about not testing the alt. and lying to me on the first trip in. He 'fessed up to it and that’s the last time I set foot in that one; even if they have the part and the good store does not.

We lost the Car Quest here about 10 years ago. They abruptly closed down one day and every time I went by I saw half a dozen CQ company cars out front. Come to find out the guy who ran this one was big into racing at the dirt track and was fudging the books to keep both himself and his buddies in free or near free parts to keep their race cars going; to the tune of 100k dollars plus.

There’s ONE O’Reillys here … opened about two years ago. I don’t think it’s going to last (unless they open more stores). I was in there a few weeks ago looking at their gauge sets singing the O’Reillys theme (but instead of “O - O - O … O’Reillys” it was “Ou - Ou - Ou … Out-of-Business”). LOL

The CarQuest here with the 3-year agreements is a company store. There IS another CarQuest store that I guess is franchised because it looks like an independent parts store but it has the CarQuest sign out front. I’ve only been to this store once (because it’s on the wrong side of town). He was the only place in town that carried a Lisle tool to compress the rockers on the Impala (when I was doing the intake gaskets). The tool looked like a kitchen implement and allowed the pushrods to be removed without removing the rocker arms (well, all but one).

I returned the 2nd “loaner” gauge set to AutoZone today. The same clerk took it back. When I asked her if someone had clearly marked the 1st set “UNFIT FOR USE”, she waved her hand at me and said (weakly), “Oh yeah, someone probably did it” - which means it probably WASN’T marked. Now I think I’m going to have to stop in again when “Mary” isn’t working to see if the set HAS been marked. The valve won’t blow out on it, but it’ll start leaking pretty badly with the missing O-Ring.

What’s with the format of this forum? It doesn’t put the latest post at the bottom (or top) - it puts it wherever you reply, which is OK, but it makes it harder to find the last post. Maybe there’s a way to change the display format??, but just the fact that it CAN be displayed this way is a problem in my opinon. The old CarTalk format was better. More conventional. This one is too generically organized.

The last time I bought anything from AutoZone involved a dead part. The electrical part of the switch in my daughter’s Mitsubishi went bad and I replaced it with a part from AZ.
After replacement the starter motor would not energize. Rechecked the switch timing and it was correct so I figured a faulty new part.

No one else around had one and since this car had to be done ASAP I found a switch at the AZ in another town. After getting home I discovered this new switch (same brand/box/etc) was in a sealed plastic bag whereas the 1st was not.
Close examination of the original “new” switch with a magnifying glass revealed some indications that it was an old part that had been palmed back off on AZ by someone who apparently wound up with a new switch and their money back.

Funny you say that because when I did my intake job on the Impala, I also replaced all the lifters (because some unsettling clicking noise had set in). Some of the lifter boxes were oil-stained, which worried me. I never buy anything unless the packaging is pristine. But in this case, I couldn’t get the lifters anywhere else at a reasonable number (other AZ in the next town wanted TWICE the price for the same Melling lifters … thought this was weird since the stores are chains, not franchised).

So far, no problems (almost two years later), but a co-worker who did the same job on his GMC Sierra about 6 months before me is suspecting a bad lifter that he had replaced (also Melling), so maybe I’m in for some bad news later this year…

OK - new year, same problem. I know I've got not only a leak, but a ONE SEASON leak. Both the '97 Taurus and the '02 Impala ran dry last year and so I filled both hoping that maybe I had a multi-season (SLOW) leak (b/c this was the first time either had run dry since I bought them both brand new). Last year I used the R-134a with the dye included (but never flashed the black light on it, unfortunately). I think I used 2.5 cans per car. Each can was $9. This year that same stuff is $20 per can (or more, depending on where you go)! So what I'm gonna do THIS time is use the R-134a without the dye (still $10/can at Wal-Mart) and add the dye separately ($7 for 5 treatments). Problem is, I'm not sure how to do it. The stuff I've seen comes in a small bottle with a twist off cap (not pressurized). It says to add it to the oil.

Do I just pour this stuff into the PAG oil and then pour the mix into the accumulator (is that where it goes)? I can look up how much I need in the shop manual (or check the sight glass ... I think it has one if I remember right), The other question is: Do I fill with the R134a FIRST, or should I put the oil/dye in first.

Lastly ... do you think the dye from last season is still in there? Maybe I don't really HAVE to add any more dye this year, just R134a???

I had a similar problem on our Honda, a one year leak. You mentioned that the high side schrader valve was leaking. I had the same thing so I bought a schrader valve kit with tool for AC from AutoZone, it was only a couple of bucks. Since the system was empty (almost), I just changed them, both high and low sides. That was last summer, still charged and working this year.

Bit of a quandry here ... I rented the gauge set (MasterCool) from AZ again and although it was pretty slimy all over, after wiping it dry it didn't appear to leak when I hooked it up (I was worried that I had gotten that bad set with the missing O-Ring that I had returned last year).

Anyway, at 4pm with ambient at 89 F and humidity at 48%, I started with the Taurus. Both gauges settled out at about 102, 103 F high and low side STATIC pressures. Then I went over to take a look at the Impala. As if on que (and exactly like last April), as soon as I hooked the gauge set up to the Impala, the high side test port on the Taurus started spewing refrigerant out like a volcano !! Obviously a loose or leaking port here. This time, however, it wasn't the white cloud I saw last year just seemed to be mostly air with only a hint of the smell of refrigerant. Could this be true? So I did the same thing as last time: I moved the gauge set back over to the Taurus to stop the hemmoraging. But UNLIKE last time, I cannot now get this port to stop leaking. Every time I remove the gauge set it just keeps coming out. I've even tried twisting the head of the gauge set clockwise several times, hoping this would pivot the core enough to minimize the leak enough so I could attempt to tighten it. No dice.

So I went to O-O-O-O-Reilly's and picked up that tool you mentioned, Keith. But I don't know what to do next. Right now the car is sitting there with the gauge set still attached. The "tool" is nothing more than a tiny thumb tool. I don't think I could get it on the test port while the port is still leaking. I can just about get the gauge set on. Do I have to wait for all the refrigerant to leak out ... and how long with THAT take? And after I either tighten the test port core or replace it (using one of the cores in the kit), am I going to THEN have to vacuum the system before refilling? And how big a deal is THAT? Can I rent a vacuum or is that a Harbor Freight item, or am I out just of luck here?

Also, do you think I could drive the car with the test gauge still attached (I think I could do this under the hood without the hoses catching on anything). Then I would drive it to a garage where the leaking refrigerant could be captured (I'm hoping). Or is there a way to capture it myself?

Had I started with the Impala instead of the Taurus, I'd at least have ONE car "fixed" (for now, at least). Instead, nothing accomplished and I'm in no-man's land right now. Fortunately, I bought a new car (2011 Equinox 1LT V6) in January (3rd vehicle), so I'm not a car down this time..

You can get a Vacuum Pump from harbor freight for ~$15.

I believe you can just replace the shrader valve there to fix that. They sell them in almost all out parts places in boxes of 5 or more for just a couple dollars.

Having said all that, I’d like to refer you back to oldschool’s comment…A/C is not really a DIY thing. You’re starting to see that now, I hope. This could have been fixed back in April.

Good luck, whatever route you choose,


Well, this is what I'd call a "Collateral Issue" - something you gotta expect (and what I've experienced) when you're doing your own car repair work.

I've GOT the replacement valve cores (2 of them) in the kit I bought ($3.49). Question is: do I just let all the refrigerant leak out or do I try to reclaim it before either tightening or replacing the core(s).

These test ports are really a poor design. There should be a manual valve on the stem below the port to prevent this type of thing. Hard to believe with all the concern over letting refrigerant leak out into the atmosphere that this design is deemed sufficient! It's really pathetic !

How 'bout a pressurized cap of some kind that I could snap down over the port? I looked for such a thing, but couldn't find it. It would just be the same thing as the end piece on the test gauge line - except it would be terminated (without any hose connection). Does such a think exist ... or could I make one?

How are you going to reclaim it?

The quick disconnect 134 fittings are actually a pretty good idea in my opinion and aged A/C systems are far more prone to leaks everywhere except the quick disconnects. I have seen a few "not as standardized as they should be" fittings in which the gauge fitting will not quite mate with the service port on the car. Maybe this is the cause?