Fixing a leak in the low pressure side A/C aluminum hard line (in a car)

[NiHaoMike]

Changing out the liquid line filter drier is just a good practice whenever the system needs service anyways.

[jeff5may]

Originally Posted by where2

I have always wondered about the need to replace the drier if a material part has not self destructed causing shrapnel in the system. I always presumed you needed to replace the drier because it is possible to take water from liquid to solid through the simple use of vacuum. I've never investigated what desiccant is being used in an A/C system to attract and contain the moisture, and whether dropping a vacuum on a "moist" desiccant boils the moisture off, drying it out again. Interesting...

The receiver dryer in a typical auto holds a few drops of moisture, 1ml or less. Its main function is to protect the compressor from ingesting any liquid or shrapnel. If the system has been open to the atmosphere, it is easier to change the receiver than pull a vacuum for long enough to boil the water out of it. If the system has failed, all the lines should be flushed.

[Daox]

All the lines should be flushed? With what? Do you flush the compressor and other bits too? How do you figure out how much oil to add back in?

[jeff5may]

Originally Posted by Daox

All the lines should be flushed? With what? Do you flush the compressor and other bits too? How do you figure out how much oil to add back in?

I use brake parts cleaner. Most cars have either hydraulic fittings with o-rings or flanges with o-rings or gaskets where stuff comes apart. At one of these connections there is an orifice or expansion valve. To check the system, take the lines off at the expansion device. If you have any garbage in the system, it will show up on the screen of this device. Handy hint: if there is a contamination problem, it will be black (they call it the black death) and obvious. Moisture will turn into acid (which eats metal and turns the oil black), smoke from a compressor burnout is black and also makes acid which turns the shrapnel black also.

If your system has the black death, you will need to flush it. Take the lines off at the compressor discharge and suction ports and remove the filter/dryer. Shoot brake parts cleaner through the lines until it comes out the other sides at the expansion device fittings. Blow inert gas the same direction to purge the lines. If you feel daring, you can jump out the low pressure cutout and run the compressor a few seconds (disconnected from its plumbing) to run it low on oil. If you ever change a compressor, make sure and ask if it comes pre-charged with oil, and if so, what kind and how much it comes pre-charged with.

If your system doesn't have the black death, you can get away with not flushing the system or changing the receiver or oil. Just make sure and pull a deep vacuum on the system and let it sit for an hour or so to give the desiccant time to out-gas if its gonna. If the vacuum comes up a little, pull it down again and wait a few minutes. If it stays below 500 microns, you're good to go. If not, the level the vacuum floats to in a few minutes will tell you what's probably wrong. Bad oil, leaky seals, moisture, etc. all float to different values pretty quickly.

If you fear you may have lost some oil, just look near the leak for evidence. Compressor oil is somewhat thick and tends to collect dirt and grime much like motor oil. To be safe, you can add an ounce or two with the charge, but make sure and get the right oil. Look it up yourself, don't ask the counter guy, he will sell you the wrong oil every time, and then you will have big problems! The type and volume of factory oil and refrigerant charge for any vehicle ever made is easy to find on the web. Seek and you will find it fast.

Off hand, I believe the L series had about 2 lbs of r134 and 8 oz of PAG oil. GM has issued TSB's for most of the older cars that says use thinner oil than what originally came in them. Most of the older models came with either PAG 100 or Pag 150 from the factory, now they are recommending PAG 46 for everything.

[NiHaoMike]

Only use nitrogen or a solvent specifically designed for HVAC work like RX11.

[jeff5may]

C'mon man! I've seen people flush out the lines with starting fluid (ether), heet (moonshine), paint thinner,acetone, etc. Real mechanics whom you would pay 300 bucks to do it. Purged with shop air from a blow gun nozzle, vacuum pulled for 20 minutes with a little diaphragm doohickey off same shop air. Presto! Customer pays $552.50 and loves it so much, they come back with another broken car.

[NiHaoMike]

It shouldn't even be necessary to flush it unless the old compressor burned out.

[Daox]

I got the car the other night. I'll be working on it over the next week or so. I'll post pictures of what I find. Suggestions are very welcome!

[Daox]

In preparation for this work, I bought myself one of these pneumatic vacuum pumps. I'd like you guys opnions on this. I have since found out that Autozone actually will 'rent' you an electric vacuum pump like I've seen so many here use. Is the electric one really that much better?

Also, I've heard you should replace the oil in the electric pumps when you use them. Is this the same oil used in the A/C system, or is this something else?

[where2]

Originally Posted by Daox

In preparation for this work, I bought myself one of these pneumatic vacuum pumps. I'd like you guys opnions on this. I have since found out that Autozone actually will 'rent' you an electric vacuum pump like I've seen so many here use. Is the electric one really that much better?

Also, I've heard you should replace the oil in the electric pumps when you use them. Is this the same oil used in the A/C system, or is this something else?

Although I have one of those "pneumatic vacuum pumps" and have used one in the past to determine whether I managed to get a reasonably solid connection on all the lines in my system by drawing a vacuum on the system and letting it sit for 24 hours. If Autozone will loan/rent you a pump, I'd use the pump. That pneumatic device requires an enormous amount of CFM from an air compressor to work properly.