StngStlkr

I searched through a lot of fan related threads, but most of them were related to the fans coming on late or not at all. I seem to have the opposite problem.

I noticed the other day that the fans kicked in at high speed (both fans, AC on) way before 185*F. Today, I turned the car on in the garage with the hood open (to verify both fans were spinning - they were) and the coolant temp pulled up in the DIC. They kicked on in high gear at 154*, spun for about 15 seconds, then went off. They came on again a few more times between 154* and 183*. Once the temp hit 183* they kicked on and stayed on. Eventually, the DIC indicated the temp had climbed to 185* so maybe it was just catching up to what the thermostat was indicating?

If I turn the AC off, the fans shut down. To me, it seems like something in the AC system is indicating they need to run.

I pulled codes, and the only one currently showing is B0367H (right actuator). I recently cleared B0516H (VSS), but it hasn't come back.

I did find this old thread that mentions the ECT and VSS being used for some of the fan control inputs:

What temp does the cooling fan turn on?

The car runs normally, temps stay normal, but I really don't want the fans running when they shouldn't be and shortening their lifespan.

I also checked the radiator, and it was pretty clean. There was a little debris at the very top, and I vacuumed that out. Coolant has about 4 years/28,000 miles on it.

Smoken1

If I turn the AC off, the fans shut down. To me, it seems like something in the AC system is indicating they need to run.

This is normal. They will shut off with a/c on after you are over 35mph

ArtClassShank

A/C will force fans on to get flow across the condenser. It's the main reason your vents continue blowing cold while stopped. Side effect is, the car will run cooler in stop and go with A/C on. If I'm using A/C and commuting through town, car runs sub 220F. If I'm windows down, A/C off, car will bounce between 228-235.


Better to test your theory with A/C off entirely, that's a more true way to ensure your fans are coming on when they're supposed too. If the car has any sort of tune on it, fan temperature parameters were likely changed.

StngStlkr

You're right. I probably should've phrased that differently. What I was getting at is that the fans did seem to operate correctly when I turned the AC off. In that, they shut down because the coolant temperature wasn't 226+.

I just got back from stop and go traffic and sitting in a parking lot. The highest the temp got on the DIC was 221* (and that was after pulling in and sitting for a few minutes). The fans did cycle on and off quite a bit while sitting and driving (hitting 35mph+ a few times). Maybe it just seems off because I haven't driven the car all that much recently. I had been driving it mostly in the early morning or at night when the outside temps weren't quite as high. This week, it's been multiple trips in the heat of the day. I just don't remember the fans cycling on right after starting the car from it sitting overnight (could be a relay issue?).

I will try testing the fans with the AC off to see what they do. That's definitely a good idea. To my knowledge, the car was stock when I got it so I don't think there's a tune on it.

foggy

With AC on, the fan are on low until 35 mph then they go off...
BUT, that setting can be over ridden by the head/system pressures that
your hi/low AC pressure sensors see. So, they could jump to hi speed if
head pres dictates. It's kinda weird if they come on high speed at idle IF
you just turn on the compressor.. It take a bit to build pressure.
Maybe your AC system needs a little attention

StngStlkr

That's what I was thinking so I went in search of AC head pressures, etc.

Here's what I've come up with:

The PCM enables the fans differently for A/C input, and coolant temperature. The PCM will enable the fans to low, when the A/C head pressure is above 219 psi, and enable to high when the pressure is above 225 psi.

From Here: Cooling Fans Won't Come On

Then, I found this:

The reason we use 212 psi as a base reading on the high-pressure side is that it is the average reading you will have at 85 degrees if everything is working properly. With systems using R-134a refrigerant, the high-side pressure usually will equate to 2.2 and 2.5 times ambient temperature. That means on an 85-degree day, you should expect to see high-pressure gauge readings between 187 and 212 psi.

From Here: Corvette Air Conditioning

So, based purely on AC head pressure hitting 219psi (the minimum for spinning up the fans), the ambient air temp would need to be between 87.6 and 99.5. I know my garage gets hot, but that hot? Maybe. Right now, it's about 93* outside, and with the heat the car gives off after being parked I could see the inside of the garage equaling that temp for a while.

StngStlkr

Just to follow up, I ran the car today with no AC (it probably stayed cooler than I did), and the fans seemed to work properly. I couldn't get it up to 235*+ (and I tried) to see if the fans would kick on high speed, but they definitely kicked in at 226* and dropped the temps back down in short order.

I pulled the top cover off the radiator & condenser to get a better look down between them. I thought maybe there would be a plastic bag stuck to the back of the condenser, but it looked fairly clean. Mostly just a thin layer of dust/dirt sort of the consistency of drier lint. I don't have a magic wand to blow compressed air and move that stuff out, but I did cut a section of old garden hose and was able to vacuum off quite a bit of the looser material.

For now, I think if there is an issue (which I'm not 100% sure of), it has something to do with AC pressure. The car is running properly in terms of ECT according to the DIC, and the fans seem to run as expected with the AC off.

I did come across this chart in another post:



Right now, outside my garage it's 86* with 70% humidity. Inside, it may be 10-15 degrees warmer (west-facing garage in FL). If I'm reading/applying that chart correctly, the AC pressure in my system could be 225+ which I believe would trigger the high-speed fans.

Update: Started the car this morning after parking it overnight (after driving it home AC off & cleaning the rad/condenser). The AC was off and no fans came on. Turned the AC on and drove it to work, about 15-20 minutes (ambient temp 82, hum 85%). Got to work, parked it and let the temps rise. Low fans kicked on at 185 and then high speed kicked in at 194 and started really dropping the temps. My best guess at this point is that the heat in my garage is keeping the AC pressures high enough to spin up the fans in a short time after starting the car. In a weeks I'll be moved into a new place that should allow for better heat dissipation. I'll be curious to see if it keeps the fans from spinning up so frequently.

lionelhutz

Its definitely ac pressure related. You've got it exactly right. My system ran low fan with ac then started going to hi fan and wasn't cooling as well either. The orifice tube was plugged. But, at higher ambient in your case it could be normal.