Question about Heating & Cooling

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I have a 2000 chevy blazer 4 wd. the ac does not work. We bought a recharge it from advanced auto and checked how much freon was in the truck. It was reading low, so we added some to the specifications given on the package. However, the air still blows out really hot. The thing under the hood that has a belt around it for the ac cuts on and off quite frequently. When we were measuring the freon, as it cut on and off the levels we were reading would go from 55 psi to 0 back up to 55. We live in Florida and its way too hot to not have the ac working. How can we fix this?

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  • christinajco May 03, 2010

    the compressor continuously cycles on and off. the pressure starts at 55psi, the compress clutch engages and the pressure drops to zero(0). As soon as it hits zero, the clutch disengages and pressure returns to 55psi, then the clutch re-engages and on goes the process. The belt turning the compressor is a serpentine belt, and the air coming out of the vents never differs from just hot.

  • christinajco May 03, 2010

    Well that doesn't give me a clue...just says to give someone all my money.
    i am mechanically inclined, just don't know about troubleshooting automotive a/c units.

  • christinajco May 03, 2010

    I thought that we weren't supposed to add more freon when it hit the max of 55 psi?

  • christinajco May 06, 2010

    Thanks so much! You were right.

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  • Master
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Hi Florida, sounds like you have a leak in the system some where. This is called short cycling on the low pressure switch, on off, on off. I am surprised that the charge you added did not do the trick. A normal charge is around 22oz. give or take. The unit under hood is the compressor which has a built in low pressure switch and as you add freon to it the clutch on the front of it will engage to start to pump freon through this system. When the clutch engages is when the pump starts and the gauge will pull down. When off it should build pressure which explains the 0 to 55 p.s.i. You don't have enough freon in this unit or it would engage and keep running. If the system was flat on freon before you started, you will need about 2- 12oz cans. Check around the fittings for signs of oil as this is what a leak will show. You can add more freon to keep the pressure up and use a mixture of soap and water to spray down fittings, hoses ect to see if you can locate a leak. You do have a leak or it would not be short cycling on the low side. Its just telling you I need more when it goes on and off like this, it has to stay on and that takes a full charge. Try adding more to see if it will continue to stay on. If not, I would have to point you to a service shop to find this leak. Special tools are needed in most cases. I am hoping you are just still low on charge. Please keep me posted and I will do my best to help you on this. Just wanted to say I have a daughter in the U.S.A.F. there in the great State of Florida. Good Luck and keep me posted.
Sincerely,
Shastalaker7
PS, If you spray down with soap and water, a leak will blow bubbles at you.

Posted on May 03, 2010

  • 1 more comment 
  • Robert Horton
    Robert Horton May 04, 2010

    Hi, no I am sorry if it sounded as though I wanted you to give all your money away at all. I am trying to save you money and get you some cooling. When you first tap the can and start the charging process, the clutch will engage and start pulling the freon from the can. This is the low pressure side you are charging through. Pressure as you charge can go over 55 p. s. i. as it empties the can. No, I would not put more then 2- 12 0z cans of the R-134a refrigerant in. What I am trying to explain to you is that if you have added lets say that amount and it continues to short cycle on its low pressure switch and the gage drops back to zero and continues to short cycle, you have other problems that may need a certified tech. I am sure that if you had the vacuum pump, manifold set that you could solve this problem. What happens when you have a small leak and the a/c is on, the compressor starts to pull in non - condensables into the system, air and moisture when it gets low enough to **** it into the place that is leaking as the low side pulls in. This causes the system to not compress the freon as air and moisture cannot be compressed. It has to be removed. It is very good that the compressor, low pressure switch is working. So, if the gage is at zero at this time when the a/c is on after you have added the charge and the compressor is short cycling, number 1 is you no you have a leak. The leak has to be found and repaired. System will need to be evacuated and recharged to function properly. I know the set up you have, can, blue hose and a gage. As you add gas the pressure can exceed 55 very easy, depending on the outdoor temperature as you charge. If you have any freon in the system at all, with it off you will have pressure on the gage. When its turned on again, the pressure will start to pull down on the gage to start the cooling process. If it gets to low, it trips/opens the low pressure switch to keep from burning out the compressor. As you have described to me what is going on, is the unit has a leak and you needed to add freon. You did the right thing. I just want you to know that if there is no change in the system after you have added enough freon, you have air in the system and it will need to be leak checked, evacuated, and recharged. You say its blowing hot air and no change. The only advise I can give you if you want to tackle this on your own, is to rent or buy a set of manifold gages, and a vacuum pump to do this. You can buy these at harbor freight tools. Attach the red hose to the high side and blue to low, and yellow to the pump after removing any freon you may have. Start the pump and open both valves on the manifold set.You will see both gages pulling down. You want to run this for about 45 min. Close both valves and watch the needles for movement up. If it holds and not moves, stays put, you will have a very, very small leak. If it starts to climb and loose its vacuum, you have a large leak which you will need to pressurize the system and try the soap test on the condenser coil and all fittings on the low and high side until you locate and repair. If you can't locate it with the soap test, we have to add dye and use a uv light to locate or a electronic leak detector. Once you have solved the leak problem you can vac the system and recharge and be on your way. I am just trying to go into some detail to help you, but to do this your self, you will need to rent or purchase these items to do the job. The problem started when the unit ran out and started short cycling and pulling in air. If it had maintained enough freon to run but not cool well, you could have got away with what you did but it was to late. Now you are up against this. Either way you will have to purchase these tools to do the job. It will cost you some money, I have no other way to tell you this and I know its a big pain. I do this everyday, mainly commercial a/c and refrigeration and know its a pain to leak check any unit. It may be in the evaporator coil which is sealed against the fire wall. I just want to be honest and upfront with you. I wish you all the best, I do. You can keep me posted if you like as I would like to know the outcome of your labor. Please let me know. Good Luck, Sincerely,
    Shastalaker7

  • Robert Horton
    Robert Horton May 08, 2010

    Thank you for the outstanding rating!! I am glad I could be of some help to you. Have a cool summer.
    Shastalaker7


  • Robert Horton
    Robert Horton Jun 05, 2010

    It's not the serpentine belt. IF it were slipping you would no right away. It drives all of the pulleys for the componants that need it . The clutch plate on front of the compressor is what engages the compressor to pump refrigerant through the system for cooling. The compressors job is to pump freon to the txv to meter freon into the evaporator coil which is where the cooling starts and back to the condenser coil where it gives off heat it has picked up to the cooler surrounding air. Basic fundamentals, it doesn't make things cold, it removes heat. Any time any a/c cycles on and off, a central system or the clutch, its low on charge is all, cycling on the low pressure switch.
    Shastalaker7
    PS Great answer Thundergod


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That is the A/C compressor and what is cutting on and off is the A/C compressor clutch, when power is supplied to it, the clutch engages the pulley to the compressor, so the compressor begins to operate and do it's job. When the A/C is off, the pulley is not engaged to the compressor. I would check the power at the plug to the compressor clutch for steady power. If not you may have a bad pressure switch or relay. I would say most likely the A/C clutch is bad. They can be replaced without having to discharge the system.

Posted on May 04, 2010

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I hate to be the one to give you the bad news, but, the air conditioning systems used in todays vehicles is far too complex for an untrained person to successfully repair all but the most minor problems such as low gas charge (which you already tried). Additionally, the freon sold in stores often often contains "sealers" that can do serious damage to the professional equipment used in shops and can gum up your system.
Especially in a state such as yours where A/C is almost mandatory, there are many competent shops that can help you. In the long run, though repairs are often expensive, it will actually save you time and money.
On a professional gauge set there is a high and low pressure gauge. Both need to be read and understood to even have the first clue as to what the problem is (you are only reading low pressure)
Electronic controls also need to be tested.
Bottom line is, invest the money....it's worth it. Can't be more honest than that!
Good Luck

Posted on May 03, 2010

  • Richard Scordino May 03, 2010

    OK...here's your other option: Go to a local community college and take a course in air conditioning systems, get a system manual for your vehicle, a set of real gauges, an evacuation pump so after opening up the system you can bring it into a vacuum to purge air and moisture so the repair works.
    After you have done that (at an expense of $1000 or more) you have half a chance of doing that repair at home. Any tech that works on A/C does all of the above before ever picking up a wrench. Why? Because that's what it takes!
    Sorry I couldn't be more helpful.


  • Richard Scordino May 03, 2010

    Perhaps you didn't grasp what I told you. I've been in the auto business close to forty years and have training in A/C systems. I know many techs that can build exotic engines and transmissions who cannot do A/C work. They do not have the training or the equipment to do that work, yet all have tons of mechanical aptitude.
    Diagnosing from here, by "remote control" without any gauge readings other than a low side reading from an inexpensive likely inaccurate gauge on a can and no electrical testing at all, is like a doctor that knows he needs an MRI to give a diagnosis for a complicated internal problem but instead givng directions on how to do a diagnosis using nothing more than guess work. In that case, the patient would likely die.
    In your case you will spend a ton of $ chasing a problem based on nothing more than suggestions that cannot be supported because there was no valid testing done. The end result is you parting with a ton of $ and eventually either having a shop try and fix not only the problem, but whatever you did to it, or, you giving up and driving around sweating all day long.
    I said what I said to help you avoid that.


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You need to replace that belt. It's slipping so it's not spinning up the compressor that actually makes the air blow cold (using the freon). Go to an authorized service for this.

Posted on May 03, 2010

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