Who has replaced A/C O-rings, common places for R134 to leak from?

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poindexternasty

New Member
Apr 29, 2008
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#1
Hey all,

I have a leaky A/C system in my 2002 GT Vert. A few days ago I started up my car and noticed it was blowing hot air. This pretty much happened overnight. One day it works, the next it doesn't. So I pop the hood to check it out and I noticed that the A/C compressor clutch was intermittently operating. I jumpered the Low Pressure Sensor Switch and the A/C compressor functioned just fine.

Ok, so at this point I'm thinking low refrigerant so I head to Auto Zone and get a can of recharge.

I charge the system to about 40 psi, or until the can was empty.

Two days later my A/C is blowing hot air again and my clutch is cycling again so OBVIOUSLY I have a leak somewhere. The recharge I added had UV dye in it to detect leaks but I haven't had a chance to take a UV light to it and find my leak.

I have read on some threads to replace the O-rings in the system to cure a leak.

My question is this: Where are the common places a mustang's A/C system would leak from? I know this can happen pretty much anywhere in the system, but are there common problems you have experienced?

Thanks a lot, I will post pics as soon as I take the UV light to it.
 
#2
The two most common points for leaking are (a) the evaporator core which is in the passenger's side dash area, and (b) the compressor seals themselves which are obviously inside the compressor. The best way to find the leak is to inject some UV dye and let it leak out. A UV light (in a dark garage is best) will then show you where the leak is with a green glow. A sniffer also works well since your leak appears to be fairly big, but the sniffers are not as cheap as the UV dye and a black light + correct goggles.

There are o-rings at every connection point. Where the two freon lines connect to the compressor, there is a single bolt thru a block of aluminum that has either two o-rings or a larger seal underneath. Make sure that bolt is tight. The hoses have several garter-spring type connectors and each has a pair of o-rings inside.

But o-rings rarely develop a leak (with the exception of the ones on the AC connector since that is held by a bolt that can loosen up over time).

The evaporator core is an expensive job so you don't want to do it until you confirm it is leaking. You will see the dye glowing where it drops out of the condensate drain under the hood if you know where that is on the passenger-side firewall. Green out of that is expensive. You might see green around the compressor pully where the seals are behind that. A new compressor is the only fix. If you do see leaks anywhere else, the o-rings are easy to replace if you have the garter-spring disconnect tool. But you will have to evacuate and re-charge to get back to normal cooling.

autozone/etc sell kits with UV dye goggles and light reasonably cheaply...
 
#5
UPDATE: Took a blacklight to the car tonight, found absolutely nothing. I checked the low pressure lines where they meet the firewall, I got underneath the car to check the A/C compressor and still nothing. Nothing at all. But I'm losing refrigerant somewhere, I know it.

When I run the car with the A/C on and then turn the car off, there is a slight hissing noise coming from in front of the engine. It is somewhere between the very front of the engine and inside the front bumper.

Just to make sure I'm not hearing something that may be normal, could one of you go crank up your stang, run the A/C for a minute or so, and then turn it off and listen for the hissing sound up front with the hood open? You may need to put your ear pretty close to the radiator area to hear it.

Thanks guys, please reply with tips!
 
#6
poindexternasty said:
UPDATE: Took a blacklight to the car tonight, found absolutely nothing. I checked the low pressure lines where they meet the firewall, I got underneath the car to check the A/C compressor and still nothing. Nothing at all. But I'm losing refrigerant somewhere, I know it.

When I run the car with the A/C on and then turn the car off, there is a slight hissing noise coming from in front of the engine. It is somewhere between the very front of the engine and inside the front bumper.

Just to make sure I'm not hearing something that may be normal, could one of you go crank up your stang, run the A/C for a minute or so, and then turn it off and listen for the hissing sound up front with the hood open? You may need to put your ear pretty close to the radiator area to hear it.

Thanks guys, please reply with tips!
Click to expand...

that hissing is normal. You have 200+ psi on the high side, 30psi on the low side, that has to equalize and it can go thru the compressor and/or the orifice tube. You might be hearing it via the condenser core, or the tubing that goes from the compressor to the condenser, etc.

As far as the dye goes, you will generally have to put it in and run for a couple of days. And a plain old black light will not work very well. The kits come with some glasses that have an orange tint to them and they _greatly_ highlight the green glow. Just make sure you check the condensate drain which is sort of hidden on the passenger firewall behind the engine. There are other ways to check if the leak is fast enough. The old soap bubble test works fine. Just spray 409 or something on every connection and look for bubbles. About the only place you can't do this is the evap core because it is hidden inside the heater box under the dash.

The compressor will generally show a leak on the front of the clutch as if it leaks thru the front seal, the dye will leak there and then sling out along the clutch.

Might be worthwhile to intentionally spill a bit of dye on something and look at it with the light/glasses so that you know what to expect. It can be very faint at times.
 
#8
You can also find leaks by tracing all the lines and looking for wet/dirty areas. When the freon leaks, a small amount of oil leaks with it. Then, dust and dirt stick to the oil, marking the location of your leak.

I'd suggest inspecting the condensor more carefully as well. It isn't uncommon to get a rock or other piece of road debris lodged in the condensor, causing a leak.

I spent a long while recently trying to find a leak on the AC system of my '97. Eventually, I found a crack in one of the tubes leading to the condenser. The fix wasn't as painful as I expected. I found a new condenser at rock auto for ~100$ shipped and the install was less than 2hrs. I used one of those 10$ air compressor driven vacuum pumps and then filled the system. Still works great! Also, I'd suggest replacing the O-rings just because you have the system apart. Evacuating and recharging the system costs 10-20x the cost of new O-rings (unless you do it yourself), so do it now as insurance. I think the O-ring set cost 5-10$ for the whole set. My ford service manual says the dryer doesn't need to be replaced unless you have trash in the system (from a compressor failure for example) or if the system was open to a humid atmoshere for a long extended time.
 
#10
No, the switch isn't the problem. I am DEFINITELY losing coolant, very quickly.

I put a 12oz can of R134a+UV dye in last night. By morning all of the refrigerant had leaked out.

I will keep looking, thanks for the tips.
 
#14
poindexternasty said:
Would a leaking condensor show itself by giving a UV reflection from the dye?

Will a regular blacklight bulb work or do I need a specific spectrum of UV light?
Click to expand...


I think normal black light will work fine, but you really need the orange-filtered goggles/glasses or it is _very_ hard to see the green glow.

It is also hard to see leaks in the condenser. As freon and dye leak out, they will migrate toward the rear of the condenser since the air thru the front end will force it that way. And now it is between the condenser and the radiator, although if it leaks much you can probably see it on the radiator fins.

Don't expect this to look like the black light demos you see at stores like Spencer's, however. :) It can be seen, but it is not that well defined. If you take your time, in a darkened area like a garage, or else at night, you will find it if it is leaking that fast...

One _really_ common leak point is the two valve cores. You can buy 'em at advanced, and the longer valve-core removal tool to fit them. It is really annoying to add freon, then notice a leak at the valve core itself, but it is common. A couple of drops of 409 or something soapy will show this up. But try to avoid letting that get into the system, as you don't want foreign liquids in there.
 
#16
poindexternasty said:
what are the valve cores? Is this where one would connect gauges to the high and low sides?
Click to expand...

yes. They are different sizes, but advanced sells both. I find that if I recharge a car that has not had an A/C problem for several years, I will find a leak at one or the other after disturbing them with the manifold gauge connectors when I evacuate and recharge. Sometimes the leak is not very big, but over time (a week or two) it will drain the thing. If it is on the high-pressure side, it will leak in a hurry when the thing is running. And those plastic caps don't seal them at all so that is no help.

They come out just like a tire valve-core. But the tool is a little longer. I think I bought the tool and both cores for 10 or 12 bucks...
 
#17
what is the process for diagnosing a problem with them? From the way you make it sound, I could have a leak at one. The low side reflects uv dye but this is to be expected as this is where the system is charged from. Would the system have to be evacuated and recharged from replacing the service ports?
 
#19
Concentrate on the condenser lines, the condenser itself, the compressor shaft seal, the service ports, and the low pressure switch. Pretty much in that order. It's hard to survey the entire condenser so take your time. I've rarely had one as simple as a spring lock connection on the top side.
 
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