Relay clicking every 3-4 seconds when AC is on

[smcguiga]

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

[Gregadeth]

You may be low on refrigerant. That would cause the AC compressor to cycle on and off.

[David T]

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.

[smcguiga]

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. :hmm: The air blows cool, but not REALLY cold, but I've kinda come to expect that from 134 vs 12.

--Steven

[Michael]

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.

[Rich]

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 (http://www.specialtauto.com/delorean-parts/relay-compartment-references.html)

[smcguiga]

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.

[Michael]

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.

[Bitsyncmaster]

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).

[smcguiga]

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...:confused0:

[smcguiga]

Yeah...has to be low on coolant, the faster I go the quicker everything is cycling...makes sense now that I've had some sleep and operating on with a fresh brain. At idle its acting normal, compressor isn't pumping as fast. As I accelerate the cycling becomes more frequent. It does seem to occur with the compressor now that I've done more testing. :slap:

ON the same note, the voltage drops from 13 down to around 9 when the compressor and fans engage. As soon as I accelerate things go back up to 13+. While driving I can see the meter drop ever so slightly when the compressor and fans engage. Time to upgrade the alternator???

Dave, After I charge the A/C, I think it might be time for your solid state fan relay. That'll cut down on the cycling and get rid of the annoying CLICK. :)

--Steven

[Bitsyncmaster]

Dave, After I charge the A/C, I think it might be time for your solid state fan relay. That'll cut down on the cycling and get rid of the annoying CLICK. :)

--Steven

Yes my fan relay is silent and will keep the fans running as long as your cycle is less than 20 seconds.

[dn010]

ON the same note, the voltage drops from 13 down to around 9 when the compressor and fans engage. As soon as I accelerate things go back up to 13+. While driving I can see the meter drop ever so slightly when the compressor and fans engage. Time to upgrade the alternator???



I have an alleged 120 amp alternator, ground bus, high flow low amp fans and mine had a nasty voltage drop when the compressor kicked on as well.

[Ron]

"Mod that keeps the cooling fans on when the AC is on" discussion moved to HERE (http://dmctalk.org/showthread.php?17556-Mod-that-keeps-the-cooling-fans-on-when-the-AC-is-on-***Split***).

[CFI]

If you switch to a dual circuit breaker setup for the radiator fans, do you need to change the breaker amperage? Can I run two 40 amp breakers or since the system is now split in two is it a better idea to run two 20 amp breakers?

[Ron]

Two 20A.

(FWIW- A popular mod to eliminate the fan fail relay uses two 25A fuses.)

[CFI]

Two 20A.

(FWIW- A popular mod to eliminate the fan fail relay uses two 25A fuses.)

Thank you

[Ron]

:thumbup: