Electric Cooling fan Wiring

[hhoelle]

I have a 2001 Yukon XL with the Red and Blue connector PCM and added electric cooling fans controlled by the PCM. I inserted a wire in terminal 42 of connector C1 (Blue) for the control of one of the two fans with A/C off. That will handle one relay. My research with a 2001 Corvette (same PCM) connector C2 uses terminal 33 for the other relays. My PCM uses that terminal for TCC Brake Switch Signal. The PCM has the ability to control two fans according to the OS. Does anyone know which terminal it uses to control the second set of relays? I have to believe if the OS has the ability to control two fans then there should be a terminal that controls all the relays. I did this to get away from the clutch fan that is so noisy and to shut off the fans at highway speeds as they are not needed. The fans are currently installed and cooling just fine as I used the A/C clutch apply signal to trigger the other relays. The only issue is when the a/c turns on only one fan operates the other one turns off and as long as the A/C compressor is on the fan stays on even at highway speeds. Has anyone added electric fans and knows which terminals control the relays? Thanks

[2xLS1]

C2 (red) 33 on those models usually controls Auto Air Recirculation operation. The System Tab>A/C>Recirc Option gives you the ability to reassign that pin to Fan 2 operation. You will lose the Auto Air Recirculation feature when you do this.

[hhoelle]

Thanks 2xLS1 I will look at that and see if I can reassign it. Recirculation is important in Florida so may have to think a little about that Though. Will try my a/c without recirc. For a few days to see how it works. Appreciate the info.

[2xLS1]

A/C air recirculation will still work with the dash button. This is an Automatic Mode that is being disabled.

[lpfeifer1980]

Great info. This helped a lot.

[1364838952]

I sure wish you would post back and tell us what you did to resolve this. I just e-fanned my '02 Silverado-411 PCM with Red/Blue connectors and I cannot get the fans to run correctly. I DID change the A/C Recirc to Fan #2 in the tune, and installed the fan control wires into the correct pin locations 42 & 33. 2nd fan (passenger side) comes on as soon as you start the vehicle and stays on. The 1st fan (drivers side) does not come on with A/C, or at any other time as far as I can tell-unless it is cycling while I'm driving and I am just not aware of it.

OP, please let me know what you did to get this resolved. I'm desperate here!

[2xLS1]

Describe what harness you are using? If you bought an aftermarket one specifically for an 02 then they are usually designed for only fan 1 wire going to the PCM and fan 2 wire triggered off the AC compressor clutch 12v.

[IARLLC]

Also, there are two different recirc switches used up until 2002. The factory recirc switches in rigs with auto AC switch at a higher pressure than the recirc switches in manual AC rigs. Both are set to only switch to recirc (which in your case is #2 fan) when the AC high side pressure is pretty high.....so if the one fan is enough to keep the pressure below that level you don't get the second fan (or the higher fan speed if wired together). For the 99-02 systems with auto AC I have installed the recirc switch from manual AC rigs to get it to cylce the fan at a lower pressure. Even still, this does not satisfy some and they go for the F-body OS or simple temp switches.

[1364838952]

My truck is an '02 silverado, but I'm running a FACTORY 2001 Silverado PCM & wiring harness. So ALL factory harness (still has the after cat o2 wiring, and also the EGR wiring, but none of that is being used. I am also running the GM fan wiring harness and relay/fuse box that came from the vehicle that I got the fans out of.

I found a post that talked about running a relay to create a (-) to trigger the 2nd fan for the A/C. My only concern with that is that if I do it that way, that fan will run any time, or all the time, that the A/C compressor is on. That means even at 60+ MPH, the HIGH speed fan will be running, when in fact it most likely will not be necessary. I've heard people talk about using a pressure switch on the A/C system so that the 2nd fan is only triggered when the A/C system reaches a certain pressure. If anyone can shed any light on how to do that, I would appreciate it.

Also, if anyone can tell me why my 2nd fan, passenger side, runs as soon as you start the engine, and it never stops, I would appreciate it.

I can trigger both fans separately through my VCM scanner controls and both fans come on, and off, with the controls so I know I have the wiring, and relays, installed correctly.

[2xLS1]

It is probably the 01 OS causing it. It is a problem with the 99-00 and some 01 OS that won't control the fans correctly. The fix is to switch to a 02 OS. There is a long thread somewhere here discussing it. I don't believe you can trigger the fans with AC pressures unless you are using a 03+ P59 with the blue/green connector and the 03+ pressure sensor.

[1364838952]

I read something similar stating that my PCM had to be reflashed with the OS from an 01-02 Camaro in order for the fans to run correctly. Can anyone confirm if that is correct? Does the Camaro use some type of A/C pressure switch that I would now need to wire in? I'm not worried about the cost, I just want it done correctly.

Thanks everyone!

[1364838952]

I think I've figured out a way to wire the fans such that BOTH fans will come on when the A/C is on, but only 1 fan will cycle on & off for engine cooling when the A/C is off. Further, NEITHER fan will run when vehicle speed is over 45-or whatever arbitrary MPH I select and put into the tune. I can also leave my A/C recirc wire hooked up as I will not need the additional pin for the PCM.

[1364838952]

For those interested, here is what I propose. Just run 1 fan off the PCM, and then for the 2nd, or high speed fan, I will use a relay to trigger it. The relay will be wired such that it will not activate the fan until the A/C compressor is active, and then only when the 1st fan is active. Here is the wiring for the relay. Let me know if you see any problems with this set up.
87 tied to vehicle ground
30 Trigger wire supplying ground signal to Fan 2 relay control
86 12V+ wire from A/C system (only hot when A/C is on)
85 Negative (-) relay wire from Fan 1 control.

Using the relay this way means that fan 2 will never be active unless A/C is on.. It also means that Fan 2 CANNOT, and WILL not run unless Fan1 is running. Fan 1 will come on as soon as the engine hits the programmed temp. Under cold start conditions, if the A/C is turned on, the fans will not come on until the PCM turns on fan #1. I guess this would be okay as the A/C condenser is going to create enough heat to get the engine temp up faster. Do you guys see any reason why it would not work this way?

Or, should I just flash my computer with a different operating system, and go that route? Which, in your mind, would be the most effective, most reliable, method?

[IARLLC]

Some of the idea seems good except for no airflow over the condenser until warmed up. That will blow up a compressor especially as you go above idle.

Using the "recirc" pressure switch cycles at a preset pressure (how much depends on whether you use the recirc switch from a manual AC rig or an auto AC rig). This can be combined with coolant temp control in a few ways.

[1364838952]

Could you please elaborate on how to use "recirc" to control the fan. My understanding is that "recirc" was just a method used to keep the A/C system from over-heating and had NOTHING to do with engine cooling, or fan control.

If you are saying that the "recirc" option found under HP TUNERS>SYSTEM>A/C>HARDWARE>RECIRCULATION FITTED>ACRECIRC can be used to control a fan, I'd sure like to know, or understand, how to do that.

Everything I'm reading is telling me that the OS must be changed as my current OS was not set up to control 2 fans and as I'm figuring out, does not correctly control the fans. I have read that an 01-02 Camaro OS should be used. If anyone has any experience changing to an F-body OS to fix this problem, I'd sure like to hear from them. I don't want to license an F-body OS just to figure out after the fact that it won't work either. I have heard that the F-bodys utilize an A/C pressure switch as well that may be necessary to get the F-body OS to work.

There is always another way to utilize the relay and that is to just set it up to run 1 fan anytime the A/C is on.. The downside to that is that it will run the fan even when cruising down the road at freeway speeds when it's not necessary.

Can anyone confirm if GM allows the electric fan to come on even at freeway speeds? Maybe I'm over-thinking this and I should just wire it up to run regardless of speed.

[2xLS1]

I would just flash a 02 Silverado OS and run the fans normally. I've done plenty like that. Then you get 2 fans running both low speed (fan 1)and 2 fans running high speed (fan 2)with coolant temps. If you need additional fans running with A/C then wire in an additional relay to supply grounds to the fan control wires triggered off the AC compressor 12V. You may need to set the diagnostics for the fan relays to no error reported if you apply grounds to the signal wires before the PCM does based on coolant temps. I have a lot of customers running around with just the coolant temp triggers on the 99-02 trucks with no issues.

[IARLLC]

The use of the recirculation pressure switch to signal fans is what 2xLS1 was writing about in several posts above. It is also described in several other forums. As 2xLS1 mentioned, you can still switch on recirc manually even if you use its pressure switch for fan control.

[1364838952]

Recirc pressure SWITCH...? What is a recirc pressure SWITCH..? Maybe this is where I'm getting lost. I'm familiar with the "Recirculation Fitted" tab in the tune where you can change it between AC RECIRC and FAN 2... Is that the "switch"? If so, I've already found that and changed it to "Fan 2" and it makes ZERO difference. I've also already removed the old A/C RECIRC wire from pin 33, and replaced it with the fan control GROUND for fan 2. Still no worky.

I'm going to move forward with changing the operating system. I will post back and let you guys know how it goes. I have a strong feeling I will find success with changing out the OS. For what it's worth-converting to Efans is a huge pain in the ass. I've now changed alternator, charging wire, radiator, electric fans with harness, had to manually adjust the throttle blade screw to bring idle air counts down, and then had to do RAF tuning again, and now OS... Definitely not worth the hassle when my old mechanical fan was not giving me any issues at all.

[2xLS1]

And the reason I said to use a Silverado calibration is that almost all 02 Yukons, Tahoes, and Suburbans are flex fuel. Your 01 is not. A Silverado calibration is going to be the closest to your 01 Yukon XL. I would avoid using a F-body calibration in a truck platform. Load your Yukon calibration as a compare file and use the copy differences tool to convert all the tables to match your vehicle. One thing though is you won't be able to put your 01 VIN in the 02 Calibration with HP Tuners ao if you need the VIN in the pcm to match your vehicle for emission testing then that is going to be another problem.

[1364838952]

I apologize for the confusion. I'm not the OP.. I just started adding to his post. I don't have a Yukon. I actually have an '02 Silverado.

My current OS is 12208322. I just looked up an '02 Silvy w/6 ltr. and 4L80E and it has the 12212156 OS which is what the F-bodies use! I see your logic! Thank you very much for that! I already have a 6.0, and a 4L80E, so that might be the best path.

Now, I'm off to learn how to change Operating Systems... Wish me luck!