5.9Excursion

I got all the lines done. Two pressure sensor bungs in the line. They use the same fitting (ford/dodge). I do not have it working yet. I ran into a problem getting the fan to speed up.

It appears (based upon some testing I did) as though the ECM does not look at the pressure sensor readings until the ECM knows the AC is running. Normally, this is done by turning on the switch in the cab which inputs to the dodge PCM and then sends a PCI bus signal to the cummins ECM to tell it to engage the AC clutch. However, I don't have a dodge PCM at all, so I can't speed the fan up?

I need to figure out how to speed up the engine fan before I charge up my AC system or the pressure will just get too high and dump the freon out...

jtharvey

Hmmm....maybe I'm being overly simplistic with my thoughts on how to make it work. I've been doing a lot of reading and talking over the last day and have an idea on how to make it work.

What I'm thinking is to take the extra bung and put a simple Hobbs switch in there. and, if I understand correctly how the fan works, if you ground one of the wires, the clutch locks up. Use the Hobbs switch to ground that wire. That way, the fan is not running unless necessary, like when the pressure starts to rise close to blow-off. Then, there would be no need for any of the Dodge switches, sensors, or controls for the AC, if I am thinking correctly.

What I don't know though is at what pressure the blow-off valve starts to dump so a Hobbs switch could be chosen that's of a value below that valve. Or, what the threads are in the bung and the best (any) place to get a Hobbs switch like that.

What do you think?

5.9Excursion

My next step was to just splice into the fan clutch control wiring, I actually already made a test connection with t-taps in all the lines. I believe the fan clutch has 12V, 5V, ground, PWM signal, and speed signal. I assume the speed signal is used by the ECM to determine current speed and to set codes if it is not what it expects. The PWM signal is coming from the ECM to control the amount of lockup. It is probably a 0 to 5 V signal, however I haven't checked yet.

It's going to be around 100 degrees today with around 90% humidity, heat index is rediculous. Just miserable out...

I may be able to try some testing today and report back. I'll see if I can alter the PWM signal and determine if the fan speeds up or not.

Keep in mind, the fan needs to increase speed based on tranny temp too (you lose this when you don't use a dodge PCM)...

jtharvey

I'll be curious to see what you find out from testing. It's going to be a few weeks before I have the engine in the truck and would be able to do some testing of my own.

I was just thinking of tapping into the fan clutch control wiring, even if it sets a code. I don't think the code would cause any problems, it would just be in the computer. I may just set it to a switch on the dash until I get the pressure switch thing figured out, if that will even work.

Trans temps are not something that I'm terribly worried about. I've got a huge cooler from a 6.0L Ford up there and with a fully built trans, things stay pretty cool. When the truck was still running, I rarely saw trans temps over 150* and I don't know that my Powerstroke fan has locked up more than a few times over the past 5 years. I do have an Autometer gauge to monitor it, so if temps started to rise I could simply pull over and if it started to become a common problem, I'd look into a way to having the fan locked up on high trans temps too. However, this Cummins will be putting out about 200 HP more than my Powerstroke was, so there will be more stress on the trans.

Anyhow, the trans temp thing is something I'll worry about later if it becomes a problem. Right now, I'm more concerned about getting my AC working, since I'm trying to get the truck running for a vacation in the middle of September and having AC on that trip would be nice.

jtharvey

A couple other thoughts I have. The Ford's 7.3 fan clutch is not electronically controlled, it's a thermal unit, so it had no way of knowing the AC was on. If the AC system didn't have any control over the Ford fan, why does it need to have control over the Dodge fan?

Also, my main concern with the fan is to keep the system from overpressurizing and starting to self vent during low speed, low airflow situations. Now, if the factory Ford pressure sensor is in place and functioning properly, wouldn't it shut off the compressor if it sensed it was too high and keep the system from self-venting?

5.9Excursion

Dodge fans were thermal units as well up to 02. One idea is to just use an 02 or earlier fan and ditch the wiring. You will get a code, but I don't know the significance.

I am using the entire ford setup to control and run the A/C, so yes high pressure should turn off the compressor to prevent self-venting the system...

jtharvey

I talked to an ASE certified guy who knows quite a bit about the Ford AC system, and I think I'm just going to run it for now, witout any fan control and see what it does.

He confirmed that with the Ford setup intact, the compressor will shut off and not begin to self vent. The only downside is a possibility of decreased cooling during low speed, low airflow. However, he also seemed to think that with the fan having only electronic lockup and it still being a viscous fan, it should pull enough air across the condenser at idle and low speed situations that there won't be a problem. I guess I'll find out.

5.9Excursion

It does move some air even at idle speeds...

I do know that with my aftermarket convertor and upgraded transmission, even with a deep pan, tranny temps (measured coming out the hot side of the tranny) can get smokin' hot on a hot day during town driving (no locking the convertor)... up to 220...

Driving down the highway on the same day w/ the convertor locked is 140 to 150...

jtharvey

Wow, that is pretty warm. I'm wondering if it's a difference between a built 48RE and my built 4R100? However, the shift programming I had with my 7.3 had the converter locked most of the time, even driving around town, and I'll probably program a similar shift stratgey into the PCS.

I'm not changing anything but stall speed on the converter during this swap...and I don't even know which way it's going. That's up to Brian at BTS. Trans, cooler, etc...will all be the same. My plan is to get the truck running with my current converter and drive the truck to Arkansas where the BTS shop is located, and let him do the converter swap there.

Back on thread topic...it's good to know that the fan does move some air even at idle.

5.9Excursion

Yeah, don't leave a rag laying on the radiator support if your fan shround isn't a tight fit

Where is your tranny temp sensor located?

I originally tried to setup my PCS to run locked from 2nd on up, but due to harsh shifts I had to wait until 50 mph in 4th to engage it. I've gotten the clutch engagement down to a positive feeling, but the 2/3 and 3/4 shift while locked was harsh...

jtharvey

LOL...thanks for the tip about the rag. I'll try and remember that one.

The trans temp sensor is located directly in the side of the trans. I asked if there was a better (ie, hotter) location for it, and have been told where it is now will see the hottest fluid. My Autometer gauge also agreed with the factory trans temp sensor when I read it with Auto Enginuity, although I don't know where it's located internally in the trans.

Have you tried dropping line pressure on the shift, if that's even possible? I've been told the PCS is pretty powerful, but have yet to dive into the actual programming of it. You may be able to drop line pressure overall slightly to ease the shifts too.

5.9Excursion

That's possible on a 4R100 but not a 48RE. The only way to change line pressure is via an adjustment bolt in the valvebody. PCS has the ability to program it in, however it just won't work with the ATS standalone valve body...

jtharvey

Gotcha. I did not know that. I see why you have decided to leave the converter unlocked until 4th then.

Mcmopar

Interesting read guys.

jtharvey

I ran by another AC shop today and talked with a guy there for quite a while about this whole setup. He pulled up his service info at the shop and from his wiring diagrams it appears that the ECM on the block is what controls the Vistronic fan setup, which we already knew. But, his diagram also shows that the signal from the Dodge transducer/sensor in the A/C line goes to the ECM on the block as well.

His thought was that if you used both the Ford pressure sensor - to tell the clutch when to activate, and the Dodge transducer in a second bung, hooked up to the engine harness, that the ECM would control the van speed when the pressure in the A/C system goes up. Which makes sense to me. Otherwise, why else would the AC controls be on the engine harness and not the chassis harness?

Right or wrong, I don't know. That's why I'm throwing it out there for discussion.