Air Conditioning leaks

I have never worked on an A/C system mostly because I don't have a great grasp of how they work, but I now have 2 vehicles with no air conditioning which isn't ideal as we head into summer. I took my truck into a shop to have it diagnosed and get a quote. 

Diagnosis: Leaks are at the lines and seals. Compressor, evaporator, and accumulator look fine. He wants to replace all the lines, seals, and orifice tubes.

Quote: $1750

It seems insane to me that it could cost this much for parts that don't do anything mechanically and the labor to install them. I know the refrigerant isn't free, but I almost laughed when I got the quote. 

I'm confident I can swap a bunch of lines and seals. I could probably just take it to a shop for a recharge. Am I confused on how difficult and time consuming this job is, or is this price out of line?

Depends a lot on the car. In theory it's not hard at all, but access in some cases is problematic, and I've seen some ludicrous prices for OE lines. Certainly worth it to price the parts yourself and look at how well you can access the various junctions before your decide.

I have an A/c system I have to fix and I've never done one either. So what I did was go to a wrecking yard and "practiced" taking stuff apart. I was able to see what it took to do the job with minimal tools so when I do the job with all my tools available it looks to be fairly easy. I will also be doing a preventative water pump, belt, thermostat, etc while I'm in there. I expect it to be time consuming but I have a pretty good idea of what needs to be done.

I also got kinda lucky and found a new compressor for my truck.The other new parts arrived last week so I hope to get it done pretty soon. Once the part s are swapped out I'll have a local shop check for leaks and fill with Rxxx. 

A/C repairs are really pretty easy as long as the evaporator coil hasn't failed. And they only make it hard because the dash usually has to come out. 

I have never had a line leak that wasn't a failed t o-ring at a joint or an aluminum line that rubbed through on something. When I fired up the XJ A/C this spring, it didn't work. I shot a little 134 in the system and listened for the hiss. Sure enough, bad o-ring. I keep an assortment on the shelf. Total repair time 30 minutes. Total cost 1 - $5 can r134. 

The daughter has developed a slow leak in her Sonic A/C. We dumped a can of dye and a can of R134 in it. The leak should show itself over the next couple of weeks or months. 

The wife's Suburban ate the compressor 700 miles from home. It will be getting the full treatment soon. Compressor, drier, orifice tube, condenser coil, and full flush. To have a shop do it would probably cost $2500 and be more than the truck is worth. It will end up costing me about $500 and a day's work. 

There is no reason to replace the orifice tube unless it's stopped up or the compressor has filled the system with schrapnel. A set of gauges will tell you if that happened. 

Seals are o-rings unless it's the compressor seal. An assortment pack is $10. Compressor seals are a little more difficult but compressors are cheap enough now that I usually replace the whole thing. 

The auto parts stores will loan you the tools if you buy the parts from them, though saving yourself a $1700 repair more than pays for a vacuum pump and gauge kit. I bought my own. The vacuum pump will also tell you if you found all the leaks.

I've done several with the harbour frieght vacuum pump. 

As to how the systems work, here is a super simplified version as I understand it. 

Have you ever gotten brake cleaner on your hand? Did your hand get cold? That cold is caused by the brake cleaner evaporating off your hand. It absorbs heat energy from your hand when that happens. An ac system uses the same principle. 

The compressor compresses the refrigerant gas.

It goes to the condenser coil where it condenses into a liquid and releases heat.

It then flows to the orifice tube which reduces the pressure.

Then into the evaporator coil where the refrigerant absorbs heat and evaporates back into a gas. This is why the air coming out of the vents is cold. 

From there to the receiver/drier, which absorbs moisture out of the system and acts as a storage area when the system isn't working hard, and then back to the compressor where the cycle starts all over. 

There is a lot of math and engineering that goes into designing the systems, but at their heart, that's how they all work. 

Pressures are pretty critical. Not enough gas in the system and the evaporator coil will be too cold and freeze up or it will evaporate before it gets to the evaporator coil and the system is weak. Too much, and some of the refrigerant is still liquid when it gets back to the compressor. The pressures also change depending on ambient temperatures. I usually use a chart like this to make sure I'm in the ballpark. 

Went through something similar on my truck.  Ended up with a seal kit from the box store (like $20) and replaced the ones that were leaking.  Check the online stores for line costs, much cheaper.  Like box store price of $100, factory of $200 but online for less than $20. 

I bought a cheap manifold gauge kit online to help diagnose.  Couldn't get it to draw a vacuum low enough and ran a bit of compressed air in the line to find the leak. 

Still had issues getting it to vacuum down far enough with a rental vacuum pump and had to pay a shop to extract and fill.  Still probably came out ahead, but SWMBO now has A/C for the Texas summer when she goes on job interviews, so worth every penny.

There are about 300 videos online of people walking through A/C repair and they helped quite a bit in calming any fears I had.

-Rob

Well, I found the leak. Pinhole in a soft line where it rubbed on a corner for 150,000 miles. Ordered the part from rock auto for $68. Access to all the connections looks pretty good once the inner fender is removed. Hopefully I'll be back in business by the weekend. 

Toyman, that description was really helpful. Thanks for that. 

In reply to Toyman01 + Sized and : Well done sir, kudos from the commercial HVAC world.  Extra points for including the PT chart.  

In reply to 11GTCS :

Glad you approved. 

I just got the report from my wife that AC is inop in the van ("it came on for like 30 seconds then wouldn't come on the rest of the drive") 

How do you start diagnosis on these systems? I'm pretty sure I can make sure the compressor kicks on, but after that I think I need to start measuring pressures?

Subbed.

I have wierd problems in the truck with intermittent function  and a leak i cant find in tbe miata.

Gonna try to learn before it gets expensive!

In reply to Robbie (Forum Supporter) :

In addition to the compressor coming on, make sure the clutch on the front of it isn't slipping. My Saab has this problem currently - it engages for a minute or two, starts slipping under any load, gets hot, slips more, ad infinitum. It will eventually kill the bearing with heat (ask me how I know). Beyond that, however, yes, a manifold with high- and low-side gauges will be needed for further diagnosis.

Robbie (Forum Supporter) said:

How do you start diagnosis on these systems? I'm pretty sure I can make sure the compressor kicks on, but after that I think I need to start measuring pressures?

I'm not a certified AC anything, but:

By far the most common problem is that it's low on refrigerant.  A simple way to check this is to open the hood and stand in front of the car when the engine is running and AC is on.  Listen for the compressor clutch to click and the tone of the engine to change as it engages.  Normal running should leave the compressor engaged all (or almost all) of the time.  A system that's low on refrigerant it will kick the compressor on, run it for a few seconds, then kick it off again as the pressure sensor shows a wrong value.  It'll wait for a bit and try again with the same result, over and over.

The right fix at that point is to find the leak and fix it (dye, replace O-rings, vacuum out, refill with the right stuff, etc), but it's pretty common for a small leak to have drained the system over a space of months.  If so then the cheap and easy way is to buy another season's use by throwing a can of refrigerant into it.

In reply to codrus (Forum Supporter) :

That's exactly what my compressor was doing. I put a can of refrigerant in the system to see if it improved or if maybe there was a pressure sensor acting up preventing it from staying on. After adding the can of refrigerant, it would stay on longer, so I was pretty confident it was just leaking out somewhere. Ended up paying a guy $300 for a diagnosis I should be able to do myself. Lesson learned.

I got it in my head that I didn't want to work on a daily driver, but I'd rather do the work than pay that kind of money to have someone else do it. 

Dusterbd13-michael (Forum Supporter) said:

Subbed.

I have wierd problems in the truck with intermittent function  and a leak i cant find in tbe miata.

Gonna try to learn before it gets expensive!

AC is out in my truck, and I can't find the slow leak in my miata either. 

Floating Doc (Forum Supporter) said:

Dusterbd13-michael (Forum Supporter) said:

Subbed.

I have wierd problems in the truck with intermittent function  and a leak i cant find in tbe miata.

Gonna try to learn before it gets expensive!

AC is out in my truck, and I can't find the slow leak in my miata either. 

Man, sounds like we're twins! 

Sorry.....

For the interested: 

Toyman's Step by Step AC Repair

Disclaimer: This is probably not the correct way to diagnose or repair an AC system. It may not even be legal. Proceed at your own discretion. I am assuming you have basic automotive knowledge. If not, get some before you try this. Some of this stuff can hurt you.  Most important, watch out for the spinny bits under the hood. Hot stuff is hot. Some of the cold stuff will freeze your skin almost instantly. You have been warned. 

Step 1. Engine on, AC on max high, doors closed, windows up. Doors closed and windows up is important.

Step 2 through something. Find the AC compressor. Is the clutch engaged and the front spinning? If no, buy a cheap AC hose with a gauge or a manifold set. Connect it and see what the low side pressure is. That's the blue gauge on the manifold. There should be a green zone on the cheap gauge. If it's less than 20 psi, the system is empty or close to it and the low-pressure cut-off switch has shut the system down, go to step whatever below. If the pressure is in the 75-100 psi range and the compressor is not turning, check the voltage at the plug behind the AC compressor clutch. If you have 12 volts, then the clutch is probably bad, test it by the book, and replace the compressor or clutch. If you don't have voltage, check the fuses. If the fuse is good, find the low-pressure cut-off switch. Bypass it with a jumper and see if the compressor starts turning. If yes, replace the low-pressure switch. If no, find the high-pressure cut-off switch and bypass it. If the compressor starts, replace the high-pressure switch. Do not leave the cut-off switches bypassed or run the system long without them! Important things will break if you do that and your repair will get much more expensive quickly. 

Edited to add: Not all systems have a low-pressure cut-off switch. The 635csi I had did not. Neither does the Kia van my son was just given. The compressor will run even with the system empty.

Step whatever: No gas in the system. The gas has escaped somewhere. The trick is to find where it got out. Your ac system has oil in it. If you keep your engine bay clean, trace out your AC lines looking for that oil and the dust/debris it will collect. Check around the connectors and areas the lines run. Check the area at the front of the ac compressor. You are looking for oil slung off the back of the pulley. It will be in line with the belt. 7 times out of 10 you can find the leak that way. Fix it and recharge the system. Times 8 through 10 you will end up dumping some gas in the system. Sometimes you can hear it leaking. Other times you have to dump some UV dye in the system, charge it and see where the dye shows up. Clean your engine bay if you have to do this. It makes finding the leak 100% easier. Edit to add: Many older systems already have dye in them. A check in the engine bay with a UV light may show the leak without adding dye to the system. 

Next step: Compressor is running, but no cold air is coming out of the vents. Whip out your trusty ac hose and check the low side pressure. If it is in the 50+- psi range, check the big line going to the compressor. Is it cold or cool? Check the little line off the compressor. Warning it may be very hot! If so, the refrigerant is probably doing what it needs to. Time to check for blend door movement. You are on your own there. Every vehicle is different and I hate working under the dash. I have come across broken blend doors twice. Neither one was fun to fix, but that was all that was wrong with the ac system.

If the compressor is running and the lines are the same temp, look at the pressure again. If it's around 75-100, the compressor has probably E36 M3 the bed and is no longer compressing. It's time to check the high side pressures, move on to the next step. 

To check the high side pressure, you need a manifold set. They are pretty cheap now. Mine came from the hammer store. Hook them up and check the pressures again. If the low side is a little high and the high side is off the chart 350 psi+, and the system is short cycling, the orifice is probably stopped up. It's a little plastic thing in a line near a line connection. They can stop up with debris. They are replaceable and that may fix the problem. Consult the interwebs to find it. Every manufacture hides them somewhere different.

If the low side and the high side stay close to the same pressure with the compressor running, the compressor is probably worn out or broken internally. As tempting as it is to replace just the compressor, don't do it. Blown-up compressors fill the system with shrapnel. The receiver/drier, orifice tube, and frequently the condenser need to be replaced as well. The rest of the system also needs to be flushed well to remove all the debris. If you fail to do these things, you will be replacing the compressor again. 

As to why the doors need to be closed. The pressures on the pressure chart are only accurate when the cool side of the system is actually cool. Always close the doors and run the system on high when checking pressures. 

That's all I have. I've successfully repaired a lot of ac systems but I'm not a trained ac repair guy. Everything I have learned came from being desperate to have cars with ac and too cheap to pay someone else to fix them. 

I am 100% certain there is a lot more to know. I am 100% certain I have forgotten to mention something. If I remember I'll edit the post in bold italic. 

Edit to add. It is tempting to add oil or stop leak or a magic fix to the system. I have never had a can of magic fix work.

Don't add oil to the system unless you are replacing components or you know the system is low or has been flushed. You can overload the system with oil. This oil usually ends up sitting in the bottom of the condenser coil reducing the effectiveness of the coil and the system. Very important. Use the correct oil if you are adding. Some of the oils used in refrigeration are not compatible with each other. There should be a tag under the hood showing the quantity and type of oil and refrigerant used in the system. If not, search the interwebs or your service manual. You do have a service manual, don't you?

Edit to add: When you buy R134, buy just that. Many of the cans that are available also have stop leak or oil, or dye in them as well. You don't want that. Oils and such should be put in the systems in the recommended quantities. You can't keep up with those quantities if every can has a little something extra in it. I have had my best luck buying R134 from Ollie's Bargains. They usually have it for $4-$5 a can. Parts stores frequently want $15/can. 

In reply to bigeyedfish :

Thanks for starting this thread.  I was going to do one soon as I need to fix my Miata's AC.

In reply to Toyman01 + Sized and :

Thanks for those steps.  That's exactly what I was hoping for.

Another thought to add.

If you are driving spiritedly, redline shifts, WOT, downshifts, rev-matching. Turn off the AC. Not only is it robbing power, but it is also possible to over-rev the ac compressor. They have a max rpm just like the engine. There are lots of tiny parts in them that can break. Most modern cars will shut off the compressor at WOT and high RPMs, but that poor clutch has to reengage every time you get out of the throttle or the RPMs drop below the threshold. Modern compressors hold up better than the old ones did but show a little mechanical empathy and turn the system off.  

In reply to Toyman01 + Sized and :

thank you thank you thank you

Been trying on my expedition.  Its functioning, but not as well as it should be. 

Compressor just keeps cycling on and off. El-cheapo gauge on the low side reads in the lower end of the acceptable "blue" range when compressor is running and is up in the "yellow" range when its off. It will not accept more refrigerant when the compressor is cycled off. 

Was going to try again (and perhaps let it run awhile with windows shut before messing). Would you just keep adding R134a timed with the compressor until its in the normal range?

Or, is it time to punt for a manifold from HF to see what the high side is doing?

I would leave it be, but its used for family trips and with two young kids...

In reply to Apexcarver :

I would splurge for the manifold set. You need to see what the high-pressure side is doing. A stopped-up orifice tube will also cause a short cycle as the pressure trips the high-pressure switch. 

Does it have rear air? Some of those systems hold several cans of refrigerant. My last E series van held something like 60 ounces of R134. Your underhood sticker should tell you.

Letting the system stabilize helps. As the cold side gets colder it will be able to draw in the R134 from the can easier. I also shake the can every few seconds. The cans are liquid R134. That needs to boil off so the system can draw it in. That's why the cans get cold.  Shaking the can encourages it to evaporate, which keeps the can pressure above the low side pressure. 

Don't turn the can upside down. Most systems are not designed to be charged with liquid. The low side port is almost always on the suction line leading to the compressor. Liquid refrigerant does not compress. If you slug it with liquid it can break those little parts in the compressor. 

In reply to Toyman01 + Sized and :

Whats a good way to send you enough money for a sandwich?

This is exactly the kind of stuff i come here for. You should write this up for the magazine. 

Dusterbd13-michael (Forum Supporter) said:

In reply to Toyman01 + Sized and :

Whats a good way to send you enough money for a sandwich?

This is exactly the kind of stuff i come here for. You should write this up for the magazine. 

I agree. That is a really good post.