Another AC question/issue....

Discussion in 'General Chevy & GM Tech Questions' started by Ape, Jun 18, 2012.

  1. Ape

    Ape Member 100 Posts

    So I've never tried using my AC on my Burb since I got it on 4-30-2011. It had many other issues I needed to address before I worried about the AC not working. The guy I got it from (best friend) had tried to convert it to 134a with the typical small kits you can buy at any parts store. He said it worked for a short time and then he stopped using it due to colder weather. But he said it was never "really" cold like he would've liked.

    So now that I've replaced the engine along with fixing alot of other mechanical issues, I've started working on the small stuff. Mostly cosmetic stuff such as paint and interior things. But since it's almost 100 today I decided to avoid sanding and bondoing and see if I could get the AC working. I bought a conversion kit a long time ago to do just that, so I pulled it out and checked the pressure in the system. The pressure showed as being low, so I followed the intructions and started filling it with the new oil/refrigerant to the reccomended pressure levels while the AC and engine were running. However, I noticed the AC unit kept coming on and shutting off in very short intervals.

    The compressor would turn on for 2 or 3 seconds and then shut off for 2 or 3 seconds continually. All the while the air in the cab of the Burb stayed luke warm. It never blew hot air, but it never blew cold air either.
    So I decided to drive it around for awhile to see if maybe it just needed to get the fluids flowing and burp itself from possible air bubbles.
    Didn't work of course, otherwise I wouldn't be here. :-/

    So here's my question.......The compressor turning off and on continually seems to be the obvious problem in this equation, but I'm stumped on why it's doing that. I don't have an ohm meter to see if it's getting a steady signal, and to be honest electrical is my weak point when it comes to cars. So I probably wouldn't know what would be a good reading even if I had one to check it with. Much less would I know where to use it or what connections to touch with it for checking the signal.
    So aside from buying a new compressor and installing it to see if that's the problem, and not taking it to a shop to spend a bunch of cash having them tell me something that "may or may not be" the issue.......Can anyone tell me if this is something typical for AC system issues? And if so what direction should I go to rectify it.
    If not, does anyone have any advice for obtaining an ohm meter and correctly using it to try and track down the issue?
  2. Ape

    Ape Member 100 Posts

    By the way.....It seems to be holding pressure so far, and I checked the rest of the system for leaks and didn't find any.
    I also know that the compressor bearings are just fine. When I sawpped the engine I spun the compressor wheel a few times and it spun for a VERY long time.
    The clutch also sounds okay to me when it's engaging for the short bursts it engages. No weird sounds as far as clunking, dragging or clicking. Just a smooth spin up that obviously effects the engine rpm with a small 100 to 200 rpm drop before coming right back up to a normal idle again. That seems typical for any AC system start up to me so.........??????
  3. Crawdaddy

    Crawdaddy All hail the Mad King!! Staff Member 5+ Years 1000 Posts Platinum Contributor

    Moved the thread as you wished. Cross-posting is not allowed.
  4. Ape

    Ape Member 100 Posts

    Thanks Crawdaddy.
  5. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    The compressor is cycling because you are low on refrigerant. The compressor is fine, otherwise it wouldn't work at all.

    You can't tell how much refrigerant you have based on system pressures. Even a low system will build enough pressure, but only for a short time so the compressor cycles. The correct way to do this is to take the compressor off, dump the oil out, put the recommended amount of fresh oil in it (somewhere around 4 ounces I suspect), re-install it and replace the dryer and orifice tube. These parts are not expensive, so it isn't going to kill the wallet. Evacuating the system and re-charging it is the ONLY way to know that you have the correct amount of refrigerant in it. Inspect the lines and components for dusty, oily stains to see if you have a leak. The common places to look are the back of the compressor, around the compressor body where the 2 halves of the compressor meet (if you have the long compressor and not the "pancake") and the high pressure valve (The cap on this valve is the primary seal, so make sure it has one on it). Those are the most common places for a GM system to leak.

    Once you have evacuated the system, you are going to have to pull a vacuum on the system for about an hour. This will get rid of any moisture that may be in the system. Next, disconnect the vacuum pump and hold the vacuum on the system for about 30 minutes to see if you have any serious leaks. Next, charge the system with refrigerant. Hook up the can and let the system pull in as much as it will from the vacuum. Now, leaving the can connected, start the engine and turn the A/C to Max. You will hear the compressor begin to cycle on and off in short bursts. The cycles will become longer as you get more refrigerant into the system.

    *NOTE* Keep the can RIGHT SIDE UP! Do not introduce liquid refrigerant into the system by turning the can upside down. It can get into the compressor as a liquid. You cannot compress liquid! Bad (and expensive) things will happen!

    Don't short the pressure switch as many do. Some folks do this to try to force the system to pull in refrigerant as the can will begin to frost and the pressure inside the can will be lower than the pressure of the system. Here's what you do: Get a 1/2 gallon pitcher of the hottest tap water you can get. Float the can of refrigerant in the hot water and it will go into the system quickly. Professional AC machines don't have "pumps", they have heaters to keep the tank from freezing up. Now you know! ;)

    Continue this until you have the recommended amount of refrigerant in the system. Don't overfill it. More is NOT better. In fact, over filling will degrade performance and risk a high pressure system failure. Once you have the correct amount of charge, remove the gauges, cap up the fittings and enjoy the cold!

    I like to use a small can of refrigerant with UV dye in it so that if I develop a leak, I will be able to find it with a UV light.

    ***SIDE NOTE*** DO NOT... EVER, EVER, EVER use refrigerant with any kind of leak sealer in it. It will ruin your A/C system, clog the orifice tube, and goo things up to the point where you will be replacing really expensive parts if you ever want it to work again! If you have added in any leak sealer, you MUST flush the system out before re-sealing and charging it!
    Last edited: Jun 19, 2012
  6. Ape

    Ape Member 100 Posts

    Obviously you know MUCH more about AC systems than I do moog! Thanks for the tips!
    But before I read this reply I did some more work on the system. And the "conversion kit" I have to switch over to 134 has the oil and refrigerant all in one can. And after reading your reply I also noticed that the cans says it also has a sealer in it as well. :-/

    So let me start off by telling you what I've done so far. I've checked over and over again for leaks and haven't found anything. And the pressure was the same this morning as it was last night. So I think I'm good to go in that arena.
    After confirming I have no noticable leaks, I fired up the system again and the clutch on the compressor was doing the same thing as yesterday. On and off in 2 to 3 second cycles. SO I drove it around for about 10 minutes to see if that had any effect and still no change.
    Next I decided to go ahead and add some more oil/refrigerant and see if that changed the rate of the clutch cycle. While doing that I noticed the cycles became closer and closer. However the charge was showing that it was getting really high?!? After the charge showed itself to be in the 60's I decided to drive it around again and see what might happen. After getting back I noticed the compressor was running for 20 to 30 seconds at a time before shutting off for 2 or 3 seconds and then starting again. The pressure still read the same though. But my air was still warm and no where near being cold.

    So I decided to go ahead and add more oil/refrig and bump the pressure up. After bringing it up another 15 pounds (per the can gauge) the compressor stayed running and never cycled. However I still have no cold air coming out of my vents????

    Now that I've read your advice I'm thinking I need to clear the system and try again?????? But I have no idea how I would pull a vacuum on the system. I assume I need some sort of special tool to do so?
    As for the dryer and orifice tube, could they be the culprit as to why I have pressure and the compressor running but still no cold air???
  7. moogvo

    moogvo Epic Member 5+ Years 1000 Posts

    If you want to make sure it is all done right, you can take it to an AC shop to have the system purged and a vacuum applied. I am not sure what they will charge you since I have access to a vacuum pump. As for your question about the tube/dryer... Mmmm. I don't think so, but you never can tell. Feel your lines when the A/C is running. One of them should be frosty while the other one will be hot. You should see water dripping on the ground under the truck on the passenger's side near the firewall. If that is the case, then the A/C is working and you have some other issue. If you put the stuff with the leak sealer in, I would have the system flushed immediately.

    At this point, I would say that it would be best to take it to a shop, TELL THEM that you have leak sealer in the system if you in fact do have it in there (otherwise it screws up the machine and they will not be nice to you!)

    When I have an A/C repair to do on my own stuff, I take the lines loose and run brake cleaner through them and then blow them out with air. Some people will tell you that this isn't good... I have never had a problem with it. I also blow brake cleaner into the evap core and the condenser to make sure all the moisture, oil and contamination comes out, then blow it out with an air compressor line. You would be amazed at what comes outta there! Usually, I get some sort of metal shavings out of it if it is an older system. Get a pack of new seals, about 5 dollars at Advance and re-assemble the system. DO replace the dryer and orifice tube if you go this deep into it. Seal it all up and take it to a shop to have a vacuum pulled on it. You HAVE to do this in order to get the right amount of refrigerant into the system and then get the right pressures!

    ***ALSO*** Ambient temperature will have an effect on the pressures you see on your gauges. You will get higher pressures the hotter it is outside. You will get COMPLETELY different pressure readings if it is 75 degrees outside, as compared to 95 degrees. This is normal operation.

    Depending on the outside temp, with the A/C on Max on a day with temps over 85, the compressor should never cycle. It should stay running all the time. Exceptions are when you are not blowing warm air through the evap core or when refrigerant levels are low. Check your lines and see if one is frosty and the other is hot. Look for the dripping underneath. let me know what you find.

    You will soon find out that there isn't much to an A/C system. It's simple really! You'll say "Crap! That was NUTHIN'!"

    Last edited: Jun 19, 2012

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