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Hi there. Hoping someone could give me some advice. I have a 99 Civic LX with 180k miles on it. The AC has never been recharged, as the car has mostly been used in cold climate and the AC was never run. However, after moving to hot hot Texas 2 years ago, the AC is no longer blowing cold, and I can hear an intermittent hissing sound under the glove box area when I run the AC. From what I've read, this thing likely needs a recharge.

I've read a bit about recharging it, and I plan to take the car to a mechanic to have the remaining refridgerant drained, and plan to recharge the system myself. I'm going to rent an AC gauge from a local parts store, and will buy a vacuum pump on Amazon. I've read a bit about testing the system for leaks and whatnot, and feel comfortable with that part. However, I have a few questions I'm hoping someone could help me with:

1. Can any recommend a good r134a brand, or does it even matter?
2. Per the sticker on my car, this AC system needs 21.2 - 22.9oz... most of the canisters I see on Amazon are either 12oz or 18oz. I don't want to under or overfill this thing, so how do I ensure I have the appropriate amount added?
3. I've read on a DIY or two that state that sometimes oil needs to be added to keep from wrecking the compressor... others mention oil already pre-added to the r134a. Can anyone provide any advice on this?

Any help would be great. I'm a broke college student who can't drive anywhere without sweating profusely, and would love to do this myself since I can't afford professional service. Thank you kindly!

 
Rep Power: 518

If the system is low, then it has a leak. May be a slooow leak, but a leak nonetheless.
Leak needs to be found, if possible. Do you know what to look for? (evidence, telltales)

Leak needs fixed once the refrigerant is recovered from the system and the system is completely empty.

That's done by watching for vacuum decay, to see if you DID fix the leak found in the previous steps.
You DID find and fix that leak already, right?

Pure.
R134a
HFC-134a
1,1,1,2-Tetrafluoroethane
No blends. No "just as good as" crap.
Not made in China. Whatever you get may not be what you think the label says. Big problem with discount stuff, and typical consumers have no way of testing the content of the products.

NO stop leak or sealants. They can ruin the high-dollar machines us pros have to use.

Oil......maybe, maybe not.
Is the oil in the can going to be correct for your compressor? (Doubt it)
How much oil has been lost? What did that leak look like? You DID find the leak earlier, correct?

You can have the pro add oil during the recharge if necessary.


Systems are accurately charged by refrigerant weight. That's another reason we use that high-dollar machine.
Consumers have to guess, and the small AC systems have very little room for error. Performance and efficiency diminishes greatly if outside of spec range.


Broke or not, Please just pay the professional to do the entire job correctly.

 
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Thanks for the helpful reply as always, ezone. I don't think I have a leak... it's just gradually stopped blowing cool air after extensive usage in hot weather. Given that it's never been recharged in 170k miles, isn't it safe to say it just needs a recharge?

Last summer, on a 95 degree day with 65% humidity, these were my readings:
- Temp: 45 degrees F (from center vent)
- High pressure: 200
- Low pressure: 27

I rented an AC gauge and vacuum pump today, which saved a lot of money. What I planned to do was have the system evacuated, and use the vacuum pump for a half hour, cut it off, and see if the system holds the same pressure for a half hour. Assuming it is leak free, I was hoping to recharge it. After reading a few tutorials and watching a video, the process looks simple enough. However, I can't tell if I need to add oil, and I can't tell how I'd know whether I put the appropriate amount in. For instance, I could do some math and probably measure out 22oz by weight from two 12oz cans, but I don't know if that's the way to go or what.

Is this really something that needs to be done at a pro shop? I really don't want to get the $100-200 shakedown, if not more...

 
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Nothing wrong with that, that seems pretty damn good.

If I must charge without a scale/station, I pay close attention to high side pressure and temperatures at various locations.

You may not get all 12 oz (x2) into the system (but it will be close), there is always a little left in the cans once they reach and equalize at the system low side pressure.

No.




Does it REALLY need more? Just add more ("top off"). No point in going to all the extra work of recovering and evacuating if you aren't going to open up the system.
Freon does not wear out.

Just add a little bit (just enough to let the high side pressure raise by ... maybe 5 PSI), see what the vent temps and high side readings are. Add a smidge more, see what the temps and pressures are. Keep going until happy.

 
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Thanks again. The pressure and temperature values I posted are from last summer when the AC was working well (I have another Civic with broken AC that I was comparing it to). Last summer, the AC could keep up with the heat, but sadly the air coming out is barely cooler than the ambient temperature. I'll check new pressures and will post them on here to see if there's much of a difference.

As for simply topping off the system, isn't there a risk of overfilling the AC? I figured discharging the system and recharging it was inherently safer than adding x amount to the existing system.

Is there a target low side and high side pressure range that I should be seeking to achieve?

Edit: rechecked pressures today... a bit different than last summer. 91 degrees outside, 55% humidity. Low side reading is 22 psi, high side is 145 psi. Temperature blowing out of the vent is 90 degrees. This would be consistent with a high side leak, yes?

 
Rep Power: 518

There is risk of overcharging either way since you don't have the equipment to charge by weight. Topping up is quicker and cheaper, but you still need to know what you are doing to reduce the risk.
Like I said, I have to top off a system from time to time without the aid of charging by weight. I use pressures and temperatures (and experience) to judge.

Yes and no. There is no cut-and-dried answer. Acceptable pressures are usually expressed in ranges, and they vary greatly depending on heat load, humidity, engine RPM, system type, temps, etc.

Check that the cable operating the water valve is still intact, the valve still works, and is actually shutting off water flow through the heater core when the temp control is at the cold position.


Feel the AC pipes going into and out of the firewall. Is one hot and one cold? Are they both "meh"?

There is absolutely no way you can know where an external leak is by using system operating pressures, you have to find any and all leaks yourself.

The pressures may indicate a possible (likely) low charge, you would have to figure out why.

 
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As far as I can tell, both pipes feel "meh" as they enter the firewall, though it's difficult to say with the insulation foam on there. I can say that I accidentally found out that the high side line is very hot where it enters the condenser, whereas the low side is meh.

Given this info, since no specific problem seems to leak out, would the next best step be to add a small amount of UV dye and some r134a to see where a possible leak might be coming from?

 
Rep Power: 518

Condenser exit point is still considered ""high side". Fan is running, doing its job, heat is being removed from the freon flowing through the condenser. Cooler at the exit point. OK.

So the suction pipe leading to the compressor is not cold, another indicator that it's inefficient (can't do its job, likely due to low charge).


The system already has pressure in it, use it to your advantage now.

If you can find the source of leakage now, you can go ahead and do the whole recover and evacuate and all that to get the leak fixed since freon needs to be empty to do so.

Look for any oily hoses (oily could mean anything less than perfectly dry), inspect around each fitting and connection throughout the system for any oil stain, dirt accumulation at any of the fittings (dirt sticks to the oil that leaked), and if the leakage is large enough you can spray soapy water all over and look for any bubbles forming.
Look for rock and road debris damage in the condenser area,

If you don't find anything this way then the UV dye could be a next step....but unless the leak is large, you won't get any results right away.....Dye is usually used to expose long term slow leakage (or maybe the tech was just too lazy to do real leak checks), although I tend to add dye to any system I have opened for any work because it just makes things easier later on.


You still need to get more freon in it to see if it will work, so I would add UV dye at this time if possible. Be careful with the dye, that crap can get everywhere.
We use little individual use tubes with straight dye, you don't want to spill it LOL. You can get a blacklight in the dark bathroom mirror and figure out what body parts you have touched since you got it on your fingers.



Next time you discover the system is low, whip out a blacklight and look for the evidence.

HTH

 
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Awesome advice... maybe this means I can temporary add enough charge to make it to my school break in 2 weeks and not die of heat stroke in between, lol.

So my question at this point... how much can I add? I've seen an r134a pressure relationship chart, but don't really understand what I'm looking at. I was advised elsewhere to add the r134a to the low side, and to add enough to make the high side pressure read 2.2 x the outside temperature. So on a 95 degree day, don't exceed 210 psi. Does any of that sound correct?

 
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I linked one somewhere around here the other day, it's a static vapor pressure chart. You can't really use it to judge much except that the system does, in fact, have some freon in it at ambient temperature. It's mostly used to determine if there are non-condensable gases (air) in the freon supply tank.

210 would be way too low.


Honda gives us a handy program that you can plug numbers into for AC work to make it a lot easier, and it's car specific....the numbers that it says are ok for your car would be bad on my car.

We have to use pretty accurate thermometers, I have 4 digital thermometers and 2 or 3 thermocouples for AC work LOL

Here's an acceptable set of numbers according to the program

Setup:
Shade, not in direct sun
Throttle propped open @1500 RPM,
Hood open, front doors open,
recirculate on,
temp set at maximum cold,
highest blower fan speed:

With a temp drop of 20* across the evaporator being acceptable:
at 95* ambient/55% humidity:
90* blower intake temp
70* vent temp
low side 45 PSI
High side 330 PSI

Acceptable pressure ranges given the above vent and intake temps: Low 35-52, high about 320-350 PSI.

BUT if I drop the intake and vent temp numbers by just 10*, then those pressures are now too high for the temperature and humidity conditions.

So don't just go by the numbers above when you do your car, since the weather and conditions will likely not be exactly the same.

 
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I'd add just little shots at a time, let the system run for a while and stabilize, and carefully watch pressures and temps when it stabilizes.

Repeat until perfect, if possible. Then quit.

 
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Wow... that's a crazy amount of variables right there. I forgot to mention, the values I gave earlier were while the car was idling (if I recall, the car idles at roughly 800rpm per the tachometer).

Since the low side 45 PSI / High side 330 PSI figures you mentioned apply to a very specific outside condition, would it hurt if I filled to a slightly lower amount to be safe? At least while I'm searching for a leak? Should I shoot for those numbers while throttle is at 1500rpm?

Thanks so much, and sorry for the million questions.

 
Rep Power: 518

@idle the high side pressure will drop some and the low side will rise some.

The compressor is not very efficient at idle speed.


Very specific conditions.
Lower pressure may be ok, maybe not. Depends.
I just plugged in some random plausible numbers off the top of my head to come up with the pressure ranges. Numbers you actually get probably wouldn't be the same as what I dreamed up.

The program starts with the setup as outlined above,
then recording vent temps in 3 places (left vent, right vent, center vent)
and recording temp at the blower intake duct behind the glovebox.
Recording shop temp (ambient in the immediate area) and humidity.
(I have a dang digital weather station on my toolbox LOL.

Look for the evidence of a leak NOW.

Adding more freon won't necessarily force it to leak any faster.


Understand why I said to let the pro charge by weight yet? LOL it's a hell of a lot easier.

 
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I definitely understand why a pro should do this stuff, with such complexity and high pressures involved. I guess the reason I was hoping to top off the system is that it seems like the leak is slow enough that I could possibly have some functional AC over the next two weeks while I await a few week break from school. We have to wear shirt and tie and such, and I'm just showing up looking like a bum right now, haha. But this way, I can add UV as well, try to find the leak over my break, replace the leaky AC part (to save money maybe), and have a pro fill it.

There's no approximate high / low pressure range I can shoot for in the meantime? If my AC was providing decent cooling last summer with high 200 psi / low 27 psi, couldn't I at least fill to that pressure while idling?

 
Rep Power: 518

Yes I'd top it up.
If you got those pressure numbers while idling, then sure try it that way and see what you get.


Then rev it up a little and see where the pressures go!

 
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Will do. Thank you. I re-read what you said about pressures changing at different rpms. Just out of curiosity, is this what you were talking about, or is this opposite what you were talking about? It's currently 84 degrees out:

@900rpm, 14 psi low / 130 psi high
@1500rpm, 5 psi low / 135 psi high

 
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Yes that's what I meant, and I think that's how I said it LOL.

and those are horribly low pressures.

 
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The differences should be more dramatic when the system has a proper charge.

 
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Awesome. Thanks again. I'll add a small amount of UV and r134a to get it back to last summer's already-low pressures and will try to hunt down the leak(s). You da man.

 
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Added a small amount of UV dye and slowly (over the course of about 30 minutes) added 12oz Dupont Suva r134a. At idle, pressures went to 35psi low / 200psi high, and at 1500rpm went to 15psi low / 250psi high. By the sounds of it, there's probably room to add a portion of another 12oz can, but for the sake of finding the leak I will leave it at these pressures for the next 2 weeks or so if it's safe to run the system at a lower charge. Fortunately, the vent temps dropped to about 55 degrees, so now my wife won't divorce divorce me... for now.

Assuming this is safe pressures, I'll pop back on with results of the leak. I suspect possible shrader valve since the low pressure cap makes a very tiny hiss noise when I remove it.

 
Rep Power: 518

How was the dye installed in it? Did the freon can have dye already in it?
Separate dye cartridge (use the full 1/4oz shot)?


I'd probably add enough freon to get the system right, then simply leave it alone until it goes low and doesn't work right again, THEN dig out the blacklight and look for the leak and deal with it at that time. But that's just me.

The Schraders can and do leak a little, but it certainly shouldn't be a rapid leakage.....

The cap is what seals the service valves, not the service valve (Schrader) itself. Those caps NEED to be on there tight, with the rubber seal intact.

 
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I bought a 1oz container of UV dye and poured about a quarter of it into the service hose before connecting it to the AC gauge, then attached the 12oz container of r134a. Then I opened the can tap all the way and very lightly opened the low side valve on the gauge... I kept the low side pressure no greater than 50-55 while filling it while my wife throttled the car at 1500rpms. Also, I held the can upside down while tipping it back and forth a little. I read some people say to keep the can upright, while others say hold it upside down to avoid introducing air. Hope I didn't screw something up.

I have a feeling the leak is pretty slow, as the AC wasn't exactly great a year ago when I'd run it, and I have a feeling this has been a pretty slow decline in performance... I was tempted to add a few more ounces to the system today, but didn't want to break something, lol.

 
Rep Power: 518

Charging with the can upside down or right side up is not about air, it's about liquid or vapor charging.

You don't want to "slug" a running compressor with liquid.

 
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I'll keep that in mind next time if I didn't already break the thing.

One thing I'm curious about... is there a way to keep air from going into the system through the service line? I would think there'd be a way to prime the line with vapor before opening the low pressure valve. Guess I should have enquired before I did it.

 
Rep Power: 518

With R12, we had to manually purge the lines before hookup because there was no internal valving to seal most of the lines.

With R134a, the lines use quick connect fittings (service valves) that keep that end of the line sealed, so the questionable area will be at the can connection. Open the can, then spin the wheel on the service connector valve a little bit to purge air?
(I don't really know, I have always had access to recovery/charging stations and have never used DIY small cans.)

The lines don't hold a lot of air, so I'd guess that even if you didn't purge it the adverse effects would (probably) be minimal --- unless there was a lot of moisture/humidity in it.
Too late now, just see what happens?

 
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It's been a few days now, and still blowing cool. I haven't gotten under the car yet, but from what I can see from above, it looks like I might have a slow leak at the low pressure shrader valve, and an even smaller one on the high side. When I charged the system partially, I cleaned out the inside of both valves and checked to make sure they weren't glowing. Today, when I removed the caps, the inside of both were glowing, particularly the low side (actually had a tiny amount of liquid). Assuming I don't find any leaks on a more thorough exam, I was thinking I'd get one of those valve core remover / installers on Amazon, and then possibly have it discharged and recharged to spec. Does that seem sensible?

 
Rep Power: 518

If it's leaking a lot then sure, replace the Schrader(s) BUT be sure to use the correct valves designed for R134a since there are many different types and sizes and some look very similar.

The plastic cap, with its rubber seal inside, is the final seal because the Schraders are not perfect and they can seep. Make sure they are installed and the seal is in good condition.



GIS is sucking, this is about all I could find that showed the seal inside the caps, but you get the idea:



HTH

 
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Thank ya kindly for all the replies. The little gasket is intact in both caps. The low pressure side (which looks to be leaking a little) makes a little "psst" noise when I take the cap off, so I think it's doing a decent job maintaining a seal.

On the subject of AC, I just realized that my AC compressor makes some noise while it's running. When I turn it on, it almost sounds like a quiet, jingly chain type of noise, or like a tiny frog chirping. I can upload the sound of it if it helps determine whether or not it's the sound of impending failure. As an aside, I did replace my timing belt 2 years ago on my own, and while I fastened every bolt to spec, I did not have a belt tensioner. It doesn't sound like the classic belt slipping noise though, so I'm not sure what to make of it. Any thoughts? Should an AC compressor run completely silently?

 
Rep Power: 518

I expect almost any compressor to make some amount of noise while operating.