AC leak in car

[luteman]

I have had experience with your problem. You have a leak and it is probably in the condenser which is a small radiator that is attached to the front of your cars main radiator, usually right behind the grill where it is vulnerable to being hit by small flying road stones.
Total removal and replacement should be in the 4 to 500 dollar range. Hope this helps!

[master53yoda]

Good description of the process.

For the DIYer, a cheap source for a vacuum pump is the compressor from an old freezer. Repair shops will often give you one. Sweat on a few fittings and you have a reasonable low volume vacuum pump. It will take a little while to pump down, but it works fine.

The use of an old compressor will remove most of the air but won't pull into a deep enough vacuum to boil off any moisture that is in the system. It requires a vacuum of less the 750 microns to remove moisture. Refrigeration vacuum pumps are oil sealed rotary vane pumps not piston pumps like a refrigeration compressor that is how they get the vacuum into the 50 to 500 micron range if left on as MPC suggested.

MPC did an excellent job of describing the required process for automotive, I was hoping someone with automotive background would reply as my background is commercial refrigeration which doesn't us the O-ring seals,

[master53yoda]

just a reminder to all to run your A/C every month or so to keep the seals lubed and the A/C in good shape. Its not to hard to do that with normal weather here in Houston... but you guys up north might need to be reminded.

good call on running monthly in the off season. Up north we end up with the defrost on and that turns on the AC but when you don't have to run the defrost or the AC running it every month for about ten minutes is needed to keep the shaft seal lubed on the compressor as it is an oil seal.

[woodturner]

The use of an old compressor will remove most of the air but won't pull into a deep enough vacuum to boil off any moisture that is in the system. It requires a vacuum of less the 750 microns to remove moisture.

I respectfully disagree. Remember that water boils at a particular temperature and pressure. On a hot summer day, say 95F, the refrigerator compressor generates enough of a vacuum to dry out the system. If one is concerned, use a heat gun to heat it up to ensure all the water boils off.

It's pretty much what a repair shop uses, just a heavier duty version. Can't speak to commercial refrigeration, no experience in that area. But the fridge compressor has worked fine for me for a few decades.

Found this link on how to build one
http://www.berkut13.com/sucker.htm

[master53yoda]

I respectfully disagree. Remember that water boils at a particular temperature and pressure. On a hot summer day, say 95F, the refrigerator compressor generates enough of a vacuum to dry out the system. If one is concerned, use a heat gun to heat it up to ensure all the water boils off.

It's pretty much what a repair shop uses, just a heavier duty version. Can't speak to commercial refrigeration, no experience in that area. But the fridge compressor has worked fine for me for a few decades.

Found this link on how to build one
http://www.berkut13.com/sucker.htm

Your giving out bad information again. Piston compressor can only develop about a 28.5 inch vacuum To remove the water at that pressure the coldest point in the system would need to remain above 100 in order to remove the moisture. Unless the car is in death valley and you can keep the compressor running for 5 or 6 hours your not going to get the moisture out of a refrigeration system with out a real vacuum pump. The OLD way when the used piston pumps was a triple evacuation procedure sweeping the system with refrigerant between vacuums and then they relied on the filters getting what was left. That was when you could vent the refrigerant, today you can't

see the chart below
in vacuum temp
26.45 - 120
27.32 - 110
27.99 - 100
28.50 - 90
28.89 - 80
29.18 - 70
29.40 - 60
29.66 - 50
29.71 - 40
29.76 - 30
29.82 - 20
29.86 - 10

The chart didn't copy correctly

a real vacuum pump will pull a negative pressure of about 29.9 in which will remove moisture at temperatures that are below freezing.

I,m going to go drive nails again. I won't respond to this kind of stuff any more.

[woodturner]

Piston compressor can only develop about a 28.5 inch vacuum To remove the water at that pressure the coldest point in the system would need to remain above 100 in order to remove the moisture.


28.50 - 90
28.89 - 80

The information is accurate, as the chart you posted shows.

The compressors I've gotten out of old freezers will generate in the range of 28 mm Hg, sometimes a little better, when measured accurately in this area. I'm not certain what type they are, they don't appear to be a piston type, but I'm not absolutely sure what type they are. Even using your 28.5 mm Hg number, your chart shows that 90F is required to evaporate the water.

All we have to do is keep the temperature above 90F and run the compressor for 10 minutes or so. If it's colder than 90F, heat the condenser with a heat gun, or warm up the engine. In most cars, just running the engine on a hot day will get it to 120F or so, plenty to dry out the water in this scenario.

As I said, I have done this for years and it works fine. It's what the local independent's do, too. One could certainly go to the expense of a better vacuum pump, backfilling with nitrogen, etc., but my point is that it is unnecessary.

So the process is:
1. warm the car to operating temperature
2. connect the vacuum pump through the charge port on the manifold guage.
3. run the vacuum pump for 30 minutes or so to make sure all the water is evaporated.
4. close the valve and remove the pump.
5. monitor the vacuum for another 30 minutes to make sure it holds.
6. charge with refrigerant.

To further emphasize another poster's point, replacement of the receiver/dryer is recommended whenever the system has been opened or any component replaced.

Just my experience and practice. It works for me, but YMMV, etc.

[master53yoda]

woodturner I give-up on you you can't admit your wrong when the whole industry is against you. Ten minutes won't dry out anything

[woodturner]

Ten minutes won't dry out anything

I'm just sharing my experience and expertise. Ten minutes is more time than most auto shops will spend drying a system and it's reasonably conservative, in my experience. Time isn't really an issue, the system just needs to reach a suitable temperature and pressure to cause the water to vaporize. Once that state is achieved, the water is vapor and time is not really an issue.

BTW, here is another link confirming the information I posted
http://www.autoacforum.com/messagevi...&threadid=7931

Perhaps you would like to explain why, in your opinion, time is important in this context? As an engineer, when someone disagrees with me, my first responsibility is to understand precisely and clearly what they mean. In most cases, these differences of perspective are due to making different assumptions or meaning different things with similar words, essentially miscommunication. Engineers are taught to first understand the problem, and a lot of times gaining this complete understanding can resolve the differences in conclusions.

[gsmittle]

Let's keep it civil, guys.

g.