Been noticing my radiator cooling fans have been running at unusual times

[econ]

Normally the fans will kick on at about 220* then turn off at 200*.

Lately I have been noticing them coming on at about 190*. Other temps too.

One time the fans were running after I shut the engine off, key removed. This is when I really started paying attention to this issue.

Then, now that I am paying very close attn to the fans, I noticed that the AC compressor clutch was engaging/disengaging on it's own. On for 3 seconds, off for 10 seconds. Something like that. And the fans were coming and going too but not exactly at the same intervals as the AC clutch engagement.

I thought to myself, OK, the AC issue is causing my fan issue perhaps since the fans come on when the AC is on.

Any idea what is causing this?

[econ]

Does the AC clutch engage when defrost is on yet outside temp is above a certain temp? I did do have this on when its warmish outside.

Any other situations where the AC clutch engages when I have not set the HVAC knob to AC?

BTW, not noticing any cool air out the vents. I simply hear the engine RPM drop in response to the AC clutch engaging and once this caught my attention I shined a flashlight at the compressor and watched it closely to confirm my suspicion.

[Mouse330]

Get the A/C pressures checked, Sounds like you need a charge

[bsn]

The AC clutch will cycle-that's normal the fans should be on anytime the clutch is engaged and will stay on if the engine temp is high enough. I assume on a Camaro if the engine is warm enough the fans will run with the engine off as many other cars do. I doesn't sound like you have a problem.

[acammer]

There are a few posts in here that get close to the truth, but maybe don't hit it right square on the head. Let's clear that up.

Attached are all the relevant fan tables for controlling the fans. It's important to note that the Fan Desired % vs ECT (coolant temp) table is not stock, it is modified to suit a 160*F thremostat and keep things as cool as reasonably possible.

As you'll note, the fans can be "triggered" by either engine coolant or AC pressure meeting a given threshold that translates to a desired percentage of fan speed (tables 18030 and 18031. Now, that desired percentage works when you have a nice variable speed fan - but we don't, just high and low, so it gets translated into a "state" (0,1,2) by table 18040. Then, that gets translated to turning on and off relays that run the fans on table 18045.

The relay control scheme can be confusing as well - some assume the fans are controlled independently, but that's not strictly true. In state 0, everything is off. In state 1 a single relay closes, which completes a circuit to allow current through both fans, in series, which results in the "low" fan speed. In state 2, two more relays close. The second relay breaks the series connection between the fans, and grounds the first fan. The third relay provides power to the now divorced second fan. With each fan now driven in parallel, rather than series, the speed increases and you get "high" fan speed. Sounds complicated, but the result is that you get at least 1 fan running on high if you should have a failure of a fan or a relay in the system.

So, what's going on with the OPs car running the fans when the engine coolant isn't hot? Well, it sounds like he's running the defrost, which does run the AC pump in order to dry the air for the best results in clearing the window. This creates pressure in the AC system, and as that exceeds 1,100kpa, it kicks the fans on low to bring air over the condenser. So, it sounds like it's working exactly like it should.

Originally Posted by Mouse330

Get the A/C pressures checked, Sounds like you need a charge

Actually, if the A/C pressure is low (needs charged) then you won't get the necessary pressure to trigger the fans at all with the AC system.

Originally Posted by bsn

The AC clutch will cycle-that's normal the fans should be on anytime the clutch is engaged and will stay on if the engine temp is high enough. I assume on a Camaro if the engine is warm enough the fans will run with the engine off as many other cars do. I doesn't sound like you have a problem.

Right on - I agree, it sounds like normal behavior.

[Mouse330]

The A/C clutch cycling on and off every 3 seconds is not normal. If the refrigerant level is low may cycle on and off rapidly to try to maintain the desired temperature. If the high side pressure is too high the compressor may shut off to prevent damage can be caused by a faulty pressure sensor, a blockage or a malfunctioning expansion valve. A faulty pressure switch can cause the compressor to cycle on and off rapidly. The pressure switch is responsible for shutting off the compressor reaches a certain level, IE high pressure. For example when the A/C cycles on the fans would be commanded on but if the high side pressure goes up to usually 400psi(Over charged, blockage, malfunctioning pressure sensor) the pressure sensor will shut the system down and the fans would be commanded off.

[acammer]

Originally Posted by Mouse330

The A/C clutch cycling on and off every 3 seconds is not normal. If the refrigerant level is low may cycle on and off rapidly to try to maintain the desired temperature. If the high side pressure is too high the compressor may shut off to prevent damage can be caused by a faulty pressure sensor, a blockage or a malfunctioning expansion valve. A faulty pressure switch can cause the compressor to cycle on and off rapidly. The pressure switch is responsible for shutting off the compressor reaches a certain level, IE high pressure. For example when the A/C cycles on the fans would be commanded on but if the high side pressure goes up to usually 400psi(Over charged, blockage, malfunctioning pressure sensor) the pressure sensor will shut the system down and the fans would be commanded off.

That's a good call - I breezed right over the short cycles. If it's really 3 seconds on, 10 seconds off, that does seem like may be on the high side, but may not that much depending on conditions. I recall 3 cycles/minute as acceptable - this would fall just inside that "acceptable" range if it is in fact 3 on, 10 off. That also does sound like low freon behavior. I am by no means an A/C systems expert, I have just enough ability to charge a system when it's empty.

It's getting warming, I think A/C performance will quickly turn into a good indicator for the overall health of the system - but maybe it's worth some actual diagnostics.

To be fair, I haven't been able to hear the A/C system on my own car in many, many years, so I have little idea how my own car behaves. The fans I'm obviously in tune with, the A/C system not so much, it works, so out of sight, out of mind. Again, good call mouse330, I read right over that.