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!

 

You could have the mechanic charge it. The machine that takes out refrigerant can also put back an exact amount by weight from a big tank. One of the quick oil change chains was doing this a few years ago. I don't remember which one or if they still do. They wouldn't do anything to the A/C other than add or remove refrigerant, but the service wasn't expensive.

Do not add oil or other additives except for UV dye (if you don't already have it). In particular never use any sort of "stop leak" product. Those seldom stop leaks, but they contaminate the system and make a proper repair impossible.

 

Thanks for the reply. I'd like to learn to charge it myself, since I think it'll save me money in the future. I was able to rent both the gauge and the vacuum pump. The guy at the auto parts store was trying to tell me that I need to add r134a with oil pre-added to it. Should I go with pure r134a or should I go with an oil premixed? Thank you much! Also, I will avoid stop leak products, and will add UV dye during recharge. Thanks!

Edit: Just to clarify, if I vacuum the system and let it sit with the gauge closed for an hour without pressure lost, I can assume I don't have a leak, and should be able to skip adding oil, yes?

 

Apparently there is a leak, or you'd never need to recharge. Refrigerant is not destroyed during operation, the only way it goes away is to leak out. But it may be too slow a leak to worry about. If you do the test with closing off the vacuum pump, and it passes, be sure to evacuate again for several minutes just before recharging. You want the highest possible vacuum so there ends up being nothing but refrigerant and oil in the lines.

Buy a can of 134a with dye in it, and one that is completely plain. Charge the dye can first with the engine off. Note that (as it says on the can) you have to hold these cans upside down so the dye doesn't get left behind in the bottom of the can. This is only if you don't already have dye, which you can see as green-yellow stuff when you take the plastic caps off of the service ports. If you do already have dye, inspect the system under a blacklight (at night or in a dark garage) and look for any dye stains that could indicate leaks.

 

Awesome reply, that makes sense. Thank you. I didn't realize that the need for replacement r134a meant an inherent leak. If my system doesn't have a leak, is there any other more likely issue I could look into? The compressor spins and doesn't make any strange noises so far as I can tell. I have owned the car since 100k miles, and it's now at 170k... there's never been any AC work that I'm aware of, or that the previous maintenance log indicates. So is there some other likely reason that this car has gradually lost it's ability to keep up with Texas heat over the past 3 months? FWIW, I hooked up an AC gauge to it last year cause it started feeling weak, and these were my readings on a 95 degree day with 65% humidity:

- Temp: 45 degrees F (from center vent)
- High pressure: 200
- Low pressure: 27

I need to obviously check it again, but if I recall the pressures are ok. Any thoughts?

 

Those pressures were OK. As an alternative to removing and replacing all the refrigerant you could try to just top up by adding more until the high side is about 2.2 x the ambient temperature in F.

Performance declining decidedly over 3 months suggests that (if the problem is lack of refrigerant) the leak is getting worse.

 

Thanks for the info, mk378! I think when I get home from school, I'll check the new pressures today and compare them to a year ago. So if I understand your comment correctly, theoretically if the system has been discharged, I should slowly fill the system with r134a until the high side pressure is 2.2x the ambient temperature... so if it's 95 degrees here, I should get the high side to read just under 210... is that correct?

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?