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Thread: Relay clicking every 3-4 seconds when AC is on

  1. #1
    Member smcguiga's Avatar
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    Relay clicking every 3-4 seconds when AC is on

    I install the relay upgrade kit a few weeks ago and now notice that when I have the AC on MAX, I hear clicking from the fuse/relay compartment every 3-4 seconds. Sometimes it happens the same time the compressor engages and I hear the click behind me coming from the engine compartment. I hear the click from the fuse/relay area every 3-4 seconds or less. Its hard to drive and determine which one it is, but I don't recall hearing it before the upgrade kit. Is this normal? If so, which relay would likely be engaging this often?

    --Steven

  2. #2
    Senior Member Gregadeth's Avatar
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    You may be low on refrigerant. That would cause the AC compressor to cycle on and off.

  3. #3
    Delorean Guru
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    The upgrade kit included an uprated circuit breaker for the fans. You were probably cycling on the old circuit breaker and now you are cycling on the low pressure switch. Sounds like you are a few ounces low on refrigerant.
    David Teitelbaum

  4. #4
    Member smcguiga's Avatar
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    Thanks for the info. So what is a normal cycle frequency for the compressor? The compressor seems to be cycling around every 7-10 seconds, while the relay inside the car doesn't exactly coincide with the compressor, so I was confused as to what its doing when it doesn't seem to cause anything to go on and off every 3 seconds. My main question was just the loudness of the relay *CLICK* and identifying which relay it could possibly be since the old ones weren't as loud.

    According to some invoices from DMCFL, they show 134A refrigerant, so I'm *guessing* that it was switch over "properly" at some point in the past. The air blows cool, but not REALLY cold, but I've kinda come to expect that from 134 vs 12.

    --Steven

  5. #5
    AKA "The Goat" Michael's Avatar
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    I was always under the impression that a proper "cycle" was around 7 seconds on, 2 to 3 seconds off. At idle it may be longer and this was with r12. Again it's been awhile, I have my pressure switch set to not cycle since it doesn't get cold enough to freeze up the evaporator (which is what the cycling is all about in the first place). You have to be careful though messing with the pressure switch because if you ever do run low in refrigerant it could harm the compressor. I am right on the edge of cutting off.

  6. #6
    Senior Member Rich's Avatar
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    Quote Originally Posted by smcguiga View Post
    Thanks for the info. So what is a normal cycle frequency for the compressor? My main question was just the loudness of the relay *CLICK* and identifying which relay it could possibly be since the old ones weren't as loud.
    The A/C cycle frequency depends on the refrigerant charge, the ambient temperature and whether the rest of the system is working OK.

    Get it to a shop or get a good set of A/C gauges on it. The shop or your gauges will tell you if it needs refrigerant. After it's topped up the cycling frequency will be what it will be.

    As far as the relay noise, it is what it is and you'll probably just get used to it. If you wonder which relays do what there's a relay diagram HERE
    March '81, 5-speed, black interior

  7. #7
    Member smcguiga's Avatar
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    I have the diagram, the weird thing is, when the relay clicks, I can't tell of anything that is changing...the radiator fans are running, then cabin fan is running, the compressor is engaged and I hear click....click...every few seconds. I would understand if this click coincided with the compressor cycling, but it doesn't. It also doesn't seem to click as often at idle. I will check the refrigerant level and just keep testing to see if I can at least determine which relay it is.

  8. #8
    AKA "The Goat" Michael's Avatar
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    Depending on who worked on it last, some vendors will setup the fans to stay on when the mode switch is set to the AC compressor selections (cool, max, bi level, defrost). I believe the factory setting (again don't quote me on this) is the fans will only run when the AC compressor runs, so if the compressor cycles every 7 seconds, so do the fans and that was taxing on the electrical system so some people set the fans to constant on when the mode switch is set.

  9. #9
    Senior Member Bitsyncmaster's Avatar
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    Check that you put the correct circuit breakers in the correct circuits when you did the upgrade. The 40 amp breaker should be in the cooling fan circuit (one with only two wires).
    Dave M vin 03572
    http://dm-eng.weebly.com/

  10. #10
    Member smcguiga's Avatar
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    Well i feel pretty silly now. It is the cooling fan relay. I had the cabin fan on low and could hear the radiator fans turning on and off. I don't understand why they are cycling so quickly though. It seems like just a few weeks ago they would turn on and stay on while the AC was running. The compressor is cycling at a normal 7-10 seconds rate. One time they were on for 1 second and then came on again for 1 second about 5 seconds later. Odd behavior...

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