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Thread: A/C clicking noise

  1. #1
    Senior Member Peripatetic's Avatar
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    A/C clicking noise

    Today was the first blue sky weekend day that also wasn't freezing. It was also the first day I drove my car where the air-conditioner was needed so I turned on the air conditioner to bilevel and cranked the temperature it all the way to blue, and the vents never blew cold. Instead every five or so seconds it would click. I noticed that the voltage meter would go up slightly until it would click again and drop to the halfway spot and repeat.

    I did a search for other A/C threads and didn't see any that matched. Does anyone know what's wrong and how to fix it?
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  2. #2
    Motors about after dark Michael's Avatar
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    You are probably hearing one of the relays clicking either for the fans or you are hearing the compressor cycling which is normal for it to engage for approx 5 to 7 seconds, click off for a few seconds and repeat. If the AC is blowing cold then it sounds like everything is OK.

    If not blowing cold then time to break out the gauges and start the flowchart of diagnostic procedures. I can tell you the voltage should not take a drastic dip with the compressor on. Minor fluxuations are OK but not major movements.
    Last edited by Michael; 04-17-2016 at 12:52 AM.
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  3. #3
    Senior Member Bitsyncmaster's Avatar
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    Your voltage is changing because when the AC compressor turns on the battery load goes pretty high with the cooling fans, compressor clutch and your blower running at the same time. If you saw the voltage changing at highway speeds you have a problem that needs to be fixed. If it was only at idle speed you have a weak alternator or weak battery.

    Your probably low on refrigerant in your AC system since your not getting cold air and rapid compressor cycling. But you need to get the AC gauges onto the system to verify what is wrong.
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    Quote Originally Posted by Bitsyncmaster View Post
    Your voltage is changing because when the AC compressor turns on the battery load goes pretty high with the cooling fans, compressor clutch and your blower running at the same time. If you saw the voltage changing at highway speeds you have a problem that needs to be fixed. If it was only at idle speed you have a weak alternator or weak battery.

    Your probably low on refrigerant in your AC system since your not getting cold air and rapid compressor cycling. But you need to get the AC gauges onto the system to verify what is wrong.
    Dave,

    What "amount" of change might you consider acceptable, and how much might be too much?

    I ask because I've always been able to see the voltage needle move, or shudder, or dip, to some degree, when engaging an additional load on the electrical system. Granted, some of the observations have been idling in the driveway, but I know on my own car that I will see the volts drop when the fans kick on. It's one way to know they are on it seems, by checking whether the needle has come down slightly from where it normally is when they aren't running.

    I used to be able to see just a slight dip in volts when I hit the brakes, until changing those bulbs out to LEDs. I've read about others seeing the same thing.


    Sept. 81, auto, black interior

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    Senior Member Bitsyncmaster's Avatar
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    Your car should be drawing less then 70 amps with everything turned on so your alternator should be able to supply that and then some with your engine RPM above idle. Now right after you start your car the battery may charge at 40 amps or more for a few seconds until it restores the power lost from using the starter.

    I have the DMCH 130 (140) amp alternator and even at idle I get no drop when the AC is on. But my fans don't cycle because of my "fan relay", my fans are also low power and my idle speed is 850 RPM and bumps to 950 RPM when the AC compressor goes on.
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    How does the 70 Amps translate to what I see on the voltage meter? Omitting for a moment any formulas or theories, what should I see on the volts gauge then? I can understand there might be some gauge inaccuracy from car to car, so perhaps it isn't exactly the same value read off it if we compared different cars, but relative to where the needle normally points when driving, are you saying it shouldn't move at all when additional loads are added or removed? I would find that hard to believe if that was the case.


    Sept. 81, auto, black interior

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    Senior Member Bitsyncmaster's Avatar
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    The alternator has a voltage regulator which may be set to 14.5 volts at ambient air temp of 70 deg F. So it should not drop that voltage until you exceed the amp specification of the alternator. The alternator it specified at a high RPM so you won't get the full current at idle.

    Now the voltage regulators do sense ambient temp and change the voltage regulation to keep the battery at full charge. Colder the voltage is higher than a warmed up summer time ambient temp.
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    Quote Originally Posted by Bitsyncmaster View Post
    The alternator has a voltage regulator which may be set to 14.5 volts at ambient air temp of 70 deg F. So it should not drop that voltage until you exceed the amp specification of the alternator. The alternator it specified at a high RPM so you won't get the full current at idle.

    Now the voltage regulators do sense ambient temp and change the voltage regulation to keep the battery at full charge. Colder the voltage is higher than a warmed up summer time ambient temp.

    If you are going to troubleshoot the A/C you shouldn't be jumping around to another system like the charging system. You most likely have a leak and are low on refrigerant. The clicking noises you hear are either the relays and/or the circuit breaker. Make sure you have installed the uprated relay kit. if you have a Ducey alternator you should replace it.
    David Teitelbaum

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    Sounds like it's a little low on Freon. I assume you have all ready switched over to R134 Freon so you can either buy a refill can with hose or a can with dye in it with hose. About $40 or less. They come with a small gauge that works well enough for the one charge you're doing. It should stop turning off and on almost immediately and stay on almost constantly as long as there is a demand for cool air i.e. your outside temps are in the 80s and above.

  10. #10
    Senior Member Peripatetic's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    Your voltage is changing because when the AC compressor turns on the battery load goes pretty high with the cooling fans, compressor clutch and your blower running at the same time. If you saw the voltage changing at highway speeds you have a problem that needs to be fixed. If it was only at idle speed you have a weak alternator or weak battery.

    Your probably low on refrigerant in your AC system since your not getting cold air and rapid compressor cycling. But you need to get the AC gauges onto the system to verify what is wrong.
    So the next day it blew cooler air, not specifically cold, but tolerable with the outside temperature at 80┬░ish. At idle the battery gauge went down one notch. At highway speed everything was fine. I was worried that it would drop too much and at longer lights I turned the AC off.

    The weak battery is likely, according to the Previous Owner's binder the battery is at least 8 years old. So, new battery and freon is on the shortlist.

    Thanks everyone!
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