looking for help with 99-02 series parallel fan control

[oldred95]

Here is what I have done so far. 99 Silverado 5.3 4L60E and so on with 2005+ electric fans wired in series parallel operation. I already have the series parallel option checked in EFI live as well as "Fan #2 Control" selected at G0106. With this I have fully functioning low and high speed fan control based on engine coolant temp. The fan control based on AC pressures however is a different story. Currently the way it operates is there is no fan operation (based on AC pressure) until the high side reaches 350 psi at which time the low speed fans turns off and when it drops to 250 psi it turns the low speed fans off. Low speed is the only fan operation allowed in this setup due to the fact that the 99-02s don't have the 3 wire variable AC pressure sensor and added logic within the PCM to enable high speed fans based on pressure.

Bare with me. This is my solution. What needs to be done is enable low speed fan operation anytime the PCM receives an AC request signal from the HVAC control head at C2 pin 17. The reason for this is it would prevent unnecessary cycling of the fans like you would get with if you were to use the AC clutch relay control at C2 pin 43. Now then there would have to be logic written into the PCM to tell it to look for an AC request signal on C2 pin 17 and once it receives it to turn the low speed fan relay on via C1 pin 42. This would give you low speed fans anytime the AC button is on as well as low speed fans based on coolant temp.

For high speed there would need to be logic written so the PCM looks to C2 pin 11 (AC recirculation switch normally open switch closes at 350 psi and opens at 250 psi) and produces an output to the high speed fan relays at C2 pin 33. This would have to be added in conjunction to the coolant temp based logic thats already there so that you would end up with low and high speed fan control based on both coolant temp and AC system status and pressure. On top of all of that it would still need to be able to turn the fans off after a given speed, say 45 mph. This would provide the most correct operation of the fans based on the limited data available to the PCM. The question is can this be done and if so by who?

[Mr. P.]

Yeah frustrating to say the least. The PCM can only trigger efan activation on the pressure read from the A/C system; since pre-2003 trucks have the old A/C controls (uses a high-side switch, not a sensor) then the PCM has no idea what the pressure of the refrigerant is - the '03+ trucks DO use a sensor, so the PCM does know exactly what is happening in the A/C compressor and hence trigger fan activation from pressures read from the high-side sending unit.

Using the A/C Request as your trigger wire - sure that would prevent efan cycling; I built a set of efans for a friend on a 2000 S-10 LS swap, and it worked well. Whenever the A/C was 'on', the low-speed fans were on; when the engine ECT got above 192, the high speed fans were triggered by the PCM.

The only workaround to the problem we have found (and implemented successfully) was to also wire the low-speed efan relay trigger wire to the A/C compressor relay - i.e. the thinking is, when the A/C compressor is running, you need the low-speed fans running (and yes the efans will cycle with the compressor); we then let the PCM control high-speed efan activation based on ECT. It's less than ideal in that you will have efans running while driving more than 45-mph (when the A/C compressor is running) but it will keep air flowing over the condenser instead of venting R143 all over the motor when idling through town at lower speeds. For a 'complete' solution, you might also consider wiring the efan high-speed relay to the A/C recirculation door, so that when the climate control is on Max-Cooling you get high-speed efans, but I've never done that for anyone (yet!).

Mr. P.

[turbo_bu]

This is probably a stupid question, but how do the fans normally work in say a Camaro with A/C? Do they work exact the same as what's in the truck OS which oldred95 is using? I am very curious in this as I am swapping a 2001 5.3 / 4L60E into a 56 Chevy and debating on whether or not to leave it as a truck OS or switch it to a F body (Camaro).

[Mr. P.]

This is probably a stupid question, but how do the fans normally work in say a Camaro with A/C? Do they work exact the same as what's in the truck OS which oldred95 is using? I am very curious in this as I am swapping a 2001 5.3 / 4L60E into a 56 Chevy and debating on whether or not to leave it as a truck OS or switch it to a F body (Camaro).

I unfortunately cannot answer authoritatively on the f-bodies (other than pulling up the shop manual and reading it!) because I have not worked on any; my entire automotive hobby has been on the GMT-800 (Gen-III trucks), I've worked on tens of them. If I were me in your shoes, what I would defiitely use is the controls from a 2003-2006 GMT-800 (Silverado, Yukon, SS, Denali, Tahoe, etc) because:

1) should be cheap and easy to find in a boneyard
2) physically fits your powertrain perfectly
3) lots of 5.3 calibrations available, you should be able to flash a factory 5.3L truck tune to it and get it to start/run perfect as-is
4) the PCM and OS support the 'contemporary' full-featured GM climate control system, with high-side A/C sensor (instead of switch)
5) fully-featured control of E-Fans
6) supports electronic DBW throttle
7) easily tuned if you want to mod the motor, and/or add forced induction - lots of tuners in the tuning community to help with your project (versus Gen-IV harness/PCM)
8) fully-supported by EFILive (and HPT as well)
9) hint - 2003 trucks came with full-return fuel system, 2004+ OS's will have 'ramped' IFR for returnless fuel system (do you want to run one or two fuel lines up from the fuel tank to the engine compartment, or external regulator, or forced induction, or stock?); all-wheel drive Escalade, Silverado SS, and Denali trucks do not have traction control in their OS's, 2WD truck OS's *will* have traction control (do you want TC button/switch on your car's dash? you might, or might not...) I would not choose to use an OS from a 4x4 truck.

Of course the other consideration is the actual mounting of the wiring harnesses, and where you will choose to mount the PCM and underhood electrical center - the F-body harness might be laid-out in a way making that package much easier to 'integrate' into your Chevy. I have no problem popping the hood to see a truck layout (electrical center & PCM hanging on the driver's fender) but you may want a much cleaner presentation underhood and the harness from another vehicle might fit better without taking a week to completely undress/reroute/solder/re-tape the harness.

The service manual lists a schematic for the 3-relay series/parallel efan setup in the F-bodies, so those PCMs & climate control systems must also fully support that functionality as well; the other difference is that they would not require the electronic DBW throttle body. Sorry to not have more real f-body experience to offer.

Mr. P.

[joecar]

On the F-body the fan#1 and fan#2 controls run the three series/parallel relays independently of A/C recirculation...

I am not familiar with A/C recirculation; what exactly does it do...? does it share a control signal with the fan#2 control...?

[turbo_bu]

Mr. P.

Thanks for the detailed summary on what to use / reasons why for the truck OS's. Right now, the donor that I have is complete with 512K PCM and wiring harness from an 01' 1/2 ton with 5.3 4L60E. Thus, my initial question on whether or not leaving it as a truck OS is better than full flashing it to an F body OS. At this point, I would rather leave it with the same PCM since I already have it and the harness. Converting to a 2003+ version might be better in the end, but I wanted to make sure I understood the tradeoffs before I made any changes to what I have.

I do have access to a 98' set of F body shop manuals. I will have to give the AC section a quick read and see how it is supposed to operate. I will have to hope that what it has is the same way the 99-02's operate.

[Taz]

In a custom / swap application you can use a truck based tune - if you swap in the system segment from a Camaro tune - which should run the fans properly with AC.

See the thread below ....

http://forum.efilive.com/showthread....h-fan-with-a-c

This option won't work well in an OEM application (i.e. the 1999 Silverado described in post #1 above). If you swapped in the Camaro system segment into this truck - certain truck features would probably become non-functional - the park / neutral and gear position indicator systems immediately come to mind.


Regards,
Taz

[Mr. P.]

... I will have to give the AC section a quick read and see how it is supposed to operate...

The climate control system is key, and a bigger issue than I first thought in my first LS-swap. 2003 is an important year for GM trucks in regards to their Delphi controls, because that year the climate control systems on GM trucks changed, and Delphi completely integrated A/C compressor control into the PCM. The climate control in pre-2003 GM trucks implement an A/C high-side pressure cut-off switch; when refrigerant pressure in the system gets above a certain set-point, the switch literally interrupts current to the A/C compressor clutch. In 2003+ GM trucks, the wiring harness & PCM changed because that climate control system uses an actual pressure sensor - so the PCM now knows exactly how much pressure is in the high-side of the refrigerant system and it consequently controls A/C clutch activation as well as Efan activation.

If you use the harness/PCM you have, you will need to either (1) use a clutch fan, or (2) wire the low-speed fan relays to energize when the A/C compressor is activated, or (3) program a stupid-low ECT set-point (like -20 degrees!) so that the efans are on all the time - this will guarantee that air is flowing over the A/C condenser when teh A/C is running. Option #1 is not swap-friendly, Option #2 works well but you will needlessly have fans on when driving over 45-mph, Option #3... you may as well hard wire the fan relays to the ignition switch. In my own LS-swap, we put a [free!] 5.3L in a 2000 S-10 (similar PCM and harness you have), I made the efan kit for it and we ended-up using Option #2 and it's worked fine - we also were able to get a local residential A/C shop to make us a couple custom hoses to graft the compressor out of a 2001 Silverado to the A/C plumbing in the S-10, worked a f'n treat (which is good in Texas summertime heat!).

I would encourage you to shop around, we can get a suitable late-model truck PCM and harness for $250-350, and likewise you can sell the one you have as well to offset its cost - for under a couple hundred bucks you can start with a much more functional engine & climate control system. BUT yes you can make what you have work alright as well, just wanted you to be aware of all the options.

[oldred95]

Here is what I ended up doing.



By setting G0903 to 50 degrees F anytime the coolant temp is above that and the AC is on the fans will turn on low after a 10 second delay. The reason for the delay is to keep from making a sudden load on the engine and causing a dip in idle speed. Just the compressor coming on pulls it down enough and even with the fans in series (low) it pulls enough to be noticeable. None the less this seems to be working good and it pulls more air then the stock clutched fan could at idle. I still have high fan on with high coolant temp which I verified tonight after a 15 minute heat soak after 30 miles of driving. The coolant temp on startup was around 225 and the high fans came on, pulled it down to 215 and then the low fans took care of the rest. Most importantly after 45 mph all fans are off so there is no excessive draw on the alternator or unnecessary wear on the fan motors.

[n8huntsman]

Sorry for posting in an old thread but I've read some stuff that seems contradictory. On the 99-02 models, does G0911, G0912, G0918, and G0919 (AC pressure trips) actually do anything? I've read that on the 99-02 models there is a pressure switch rather than a pressure sensor, therefore, I don't see how it would really know what pressure it's at. What am I missing?
Thanks