Fan Duty Cycle Question

[bigceltic]

No issue with my truck (that I know of!) but rather curiosity (goes with my name I guess!). I added "Fan DC" to my smarty touch screen and noticed when it was hot, and I had AC going, the Fan DC value would jump to 99 (%) and then drop to 15 (%). I keep reading about the "roaring sound" that the fan is supposed to make but I really do not notice it change much at all. How loud is it supposed to get? It was at (supposedly) 99% and yet it pretty much sounded the same as it always does. I tried the test where when the truck is hot and stopped (engine off) I tried spinning the fan - there is resistance and it does not free spin (stops almost immediately). I have no codes (per the Touch) - hard or soft (that I can see). Am I being paranoid, or is there something I should look into?
Thanks,
George

 

[Wayne M.]

Yes that’s a great fan design! The only true way to know if you’ve got a fan issue is a DTC and if you’re having poor AC performance due to poor condenser cooling/ high hi side pressures. Also if you have good enough diagnostics/ scan tool, I think you can see fan RPM.

 

[Ozymandias]

Yes that’s a great fan design! The only true way to know if you’ve got a fan issue is a DTC and if you’re having poor AC performance due to poor condenser cooling/ high hi side pressures. Also if you have good enough diagnostics/ scan tool, I think you can see fan RPM.

Correct, you'll see command and return value of Fan rpm. And they are more or less independent from engine rpm.

 

[Wayne M.]

they are more or less independent from engine rpm.

Because the crank to fan pulley ratio is not 1:1.

 

[bigceltic]

Thanks to all for the quick responses. No AC issues at all so I guess everything is A-OK and I got one of the quiet fans!

 

[AH64ID]

The fan DC will jump to 99% when it wants to increase the fan rpms and as soon as the increase starts to happen it will drop the DC to obtain the desired fan rpms. The fan clutch is fairly slow to react, especially at lower rpms, which is why the DC maxes out so quick. This is why you don't always get the loud fan sound. I've found that fan rpms is a much better gauge to watch that DC.

Also, your fan is a bit more aggressive for AC and ECT than it was stock. The 99% on cycle is stock thou.

 

[Tuesdak]

You are close but not quite asking the right questions. I suggest you set a display, of many, up like I did to monitor AC performance in the thread below. Then watch your fan for going much below 600 RPM on a cold day: it shouldn't or it's worn out. Your AC system will vent over 450psig and OOPSIE no high pressure cut out in the ECM for 2003-2007 5.9's. Link in depth here. Fan don't get going the system blows a pound out the relief valve. So set the Smarty AC Pressure alarm "Beep!" and "red light" at 400psig. Immediately turn down the blower to low or shut the AC off. 430 psig shut AC off as you have zero room left.

https://www.turbodieselregister.com...thermal-dispersant-on-an-ac-condenser.264486/

 

[mwilson]

My temp gauge has to be at 210 before my fan makes a noticeable roar. That only happens on long hills towing the trailer.

 

[Wayne M.]

My temp gauge has to be at 210 before my fan makes a noticeable roar. That only happens on long hills towing the trailer.

Yup, you really have to work the truck hard to tax the cooling system.

 

[bigceltic]

You are close but not quite asking the right questions. I suggest you set a display, of many, up like I did to monitor AC performance in the thread below. Then watch your fan for going much below 600 RPM on a cold day: it shouldn't or it's worn out. Your AC system will vent over 450psig and OOPSIE no high pressure cut out in the ECM for 2003-2007 5.9's. Link in depth here. Fan don't get going the system blows a pound out the relief valve. So set the Smarty AC Pressure alarm "Beep!" and "red light" at 400psig. Immediately turn down the blower to low or shut the AC off. 430 psig shut AC off as you have zero room left.

https://www.turbodieselregister.com...thermal-dispersant-on-an-ac-condenser.264486/

First of all, this has been really cool (pun not intended!) now that I know what to look for and have the proper items displayed on the Touch gauge. I am also glad I listened to Tuesdak and set the alarm before I started my truck yesterday after work. It was 92F outside, and I started the truck and turned on the AC as usual, and I watched the AC pressure shoot up quick and it blew through my alarm value of 400 and I immediately turned the AC off - it hit a high of about 425 before going down. The Fan DC had jumped to 99 and the Fan RPM was climbing but obviously not fast enough. Who knows how many times this may have happened in the past. Now that I am monitoring it, I can keep an eye on it. Thanks so much. Experience like this is what makes TDR such a great forum. Other than that, the fan seemed to work fine and AC pressure was kept in check when stopped for a light or stop sign (pressure would begin to ramp up, fan RPM would increase to 800+ and AC pressure would drop).

Thanks again to all!

 

[Tuesdak]

My memory is rusty, but, what was your fan RPM at idle while the AC pressure was running away? I fought my old fan clutch way too long and would get upper 300 RPM readings coming off the freeway. When It couldn't lock in coming off the freeway I replaced it and recall it wouldn't go below 600 RPM at idle with a new MOPAR fan clutch.

 

[bigceltic]

I will pay attention and record it tonight on the way home and let you know.

Update: Starting up after work, outside temp 93F, started and Fan RPM was 350ish and then the pressure started to rise, hitting a high of 376psi, and fan sped up to 830 and stayed around 15% DC/830RPM. Drove home using AC the whole way, stopped at store, and when I restarted truck, Fan RPM was 837, ECT 191F and it was still 89F outside. Only diff between today and yesterday was that I ran the AC on the way into work today, but did not run it the day before.

 

[Wayne M.]

You’re on the right track, bigceltic. My fan showed no issue whatsoever, but my AC cooling was lackluster on a hot day. I just gambled a fan and that was the issue.
Next advice- DO NOT. DOOO NOOOTTT buy an aftermarket fan clutch. Mopar only!

 

[bigceltic]

You’re on the right track, bigceltic. My fan showed no issue whatsoever, but my AC cooling was lackluster on a hot day. I just gambled a fan and that was the issue.
Next advice- DO NOT. DOOO NOOOTTT buy an aftermarket fan clutch. Mopar only!

So are you saying that my data indicates my fan clutch is on the way out and needs to be replaced? I think so, but wanted to confirm. Thanks.

 

[Wayne M.]

So are you saying that my data indicates my fan clutch is on the way out and needs to be replaced? I think so, but wanted to confirm. Thanks.

That’s what I’m implying.
The issue is that there’s no feedback logic in the fan clutch, to compare, a modern automatic transmission can set a fault for torque converter slippage or incorrect ratio fault for a slipping clutch pack or band. This is because there are speed sensors at both ends of the transmission, unlike the fan. It cannot pick up on slippage.

 

[bigceltic]

That’s what I’m implying.
The issue is that there’s no feedback logic in the fan clutch, to compare, a modern automatic transmission can set a fault for torque converter slippage or incorrect ratio fault for a slipping clutch pack or band. This is because there are speed sensors at both ends of the transmission, unlike the fan. It cannot pick up on slippage.

Ok, thanks. Ordering a MOPAR fan clutch now! Looks pretty easy to install.

 

[User113]

Tuesdak,

I read your post "Results of a Thermal Dispersant on an AC condenser" and looked at the pictures. Your Smarty shows monitoring of AC-P of your 2003 model year truck, but AC-P is not on the "Supported PID's for MY 2003 - 2004." It doesn't show up until the 2004.5-2005.5 list. Is there anything special that needs to be done to monitor the AC-P PID in a MY 2003-2004?

BTW, I really appreciate all the work you did in tracking that information down and sharing.

 

[Tuesdak]

I will pay attention and record it tonight on the way home and let you know.

Update: Starting up after work, outside temp 93F, started and Fan RPM was 350ish and then the pressure started to rise, hitting a high of 376psi, and fan sped up to 830 and stayed around 15% DC/830RPM. Drove home using AC the whole way, stopped at store, and when I restarted truck, Fan RPM was 837, ECT 191F and it was still 89F outside. Only diff between today and yesterday was that I ran the AC on the way into work today, but did not run it the day before.

Just to confirm: 350 RPM IMO indicates the fan clutch is worn/aged out. It's not spinning fast enough when kicked out for the working fluid to get moving in the clutch to lock it in or simply too worn to move. I should have tracked the RPM of my new and old clutch better.

Tuesdak,

I read your post "Results of a Thermal Dispersant on an AC condenser" and looked at the pictures. Your Smarty shows monitoring of AC-P of your 2003 model year truck, but AC-P is not on the "Supported PID's for MY 2003 - 2004." It doesn't show up until the 2004.5-2005.5 list. Is there anything special that needs to be done to monitor the AC-P PID in a MY 2003-2004?

BTW, I really appreciate all the work you did in tracking that information down and sharing.

I had a July production 2003 that would NOT allow high idle without an ECM replacement: Maybe. I recall the 2004 ECM's were different. Regardless I would get hold of Smarty Support and ask them to add this. Point of fact they changed the AC pressure range for me when I pointed out the warning range was set wrong (too low and always red).

 

[Mikey-KE7LBB]

I have a mechanical Ford fan drive on my '09.. It works well, but A/C performance is dismal until the thermostat opens a few times....

 

[bigceltic]

Ok, new fan clutch is in. Not too hard a job at all. At start up (after install engine cold, 58deg outside), now the fan is running at 800+ rpm vs 300-something before. Thanks for all the help, especially Tuesdak, for helping me diagnose it.

Update: Just got back from a grocery run, and the fan is definitely running better than it did before. Low speed was in the 500s rather than the 300s like before. I wonder how long it has been bad. Last summer I had to get my AC repaired (new compressor, etc) to the tune of $1700 - I prob could have replaced the fan clutch years ago for under $500 and may have saved my AC. Live and learn. I will definitely be monitoring it from now on and replacing at signs of trouble.