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Electric Fans on 2002 1500HD with Proper A/C Control

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Old 08-09-2018, 04:08 PM
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Default Electric Fans on 2002 1500HD with Proper A/C Control

All,

So I'd first like to reference the following post for the inspiration in starting this whole process.
https://www.gmfullsize.com/threads/i...y-2001.229730/
For reference my truck is a 2002 Chevy Silverado 1500HD. Being a 1500HD I already had the wider radiator needed to fit the 2005-2006 electric fans. I know depending on the vehicle these are going into you may need a different size radiator, but all of that is covered in numerous other locations on the internet so do your own research before buying parts.

Now, there are some differences in what I did vs the above link. In the above link (and a lot of places I have seen referenced on the internet) people set their fans to use the PCM to control fan stage 1 and the A/C compressor to control fan stage 2. This is done for a couple of reasons: 1. The output pin C2-33 is used to control the recirculate door on the 1999-2002 trucks. 2. The 1999-2002 trucks only have a A/C high pressure switch wired to the PCM instead of a A/C high pressure sensor like the 2003+ trucks. This prevents the PCM from controlling the speed of the fans based on A/C load.
So, lets discuss the two things to overcome here:
1. The output pin C2-33 controlling the recirculate door. This has been covered in various locations around the internet, but the main reason this exists is to allow the PCM to force the HVAC system to go into recirculate mode whenever the A/C high pressure side gets too high from insufficient cooling air flow over the A/C condenser. While there is still a chance this could happen with the electric fans, this is a much lower probability since you will have quite a bit of air flow over the condenser even at idle with the electric fans. I will give the disclaimer that I am from a northern state where we rarely break 100*F, so you folks down south are on your own. For me (and a good portion of people on the internet) this isn't a concern and this pin should be re-purposed to control the 2nd fan stage without any issues.
2. Only having a A/C high pressure switch instead of a A/C high pressure sensor. This is one I have not been able to find a direct confirmation from anyone anywhere on the internet so as far as I can tell I am the first to do this (or at least document the work where everyone can see it). What you need here is a 3-wire pressure sensor from a 2003+ truck and the associated wiring from the sensor to the PCM. Putting in this sensor will require programming changes to activate it. The reason we are able to make this sensor work is because the F-body cars came with a A/C high pressure sensor and the same 411 PCM as the 1999-2002 trucks and thus the code for it to work exists in the PCM when properly setup. However, one oddity is that the F-body cars came with a variable displacement A/C pump and thus didn't have the A/C low pressure cycling switch like the trucks. In the F-body the compressor would be commanded on and then a swash plate in the compressor would vary compressor flow to maintain a constant low side pressure. On the trucks 1999-20?? there is a fixed displacement pump which thus needs a low side pressure switch which cycles the compressor to keep everything from freezing up. Luckily for us, this switch is hard wired right in series with the A/C compressor clutch control so there is no programming differences, the low pressure switch takes care cycling the compressor, the PCM just takes care of commanding the compressor to run (at least as far as I can tell).


Programming:

To make this work some changes will need made to the PCM above and beyond the typical cooling fan tweaks everyone does. For all of this work I used as much as the default settings as I could from a 2005+ truck settings file. I figure GM put all the R&D time and money into coming up with these numbers so they are the best place to start. Below is a summary of the settings changes:
1. Set the cooling fan on/off temps, compressor on/off pressures, on/off speeds, minimum run times, etc. for fan stages 1 & 2 per the 2005+ settings file. Do note there is an on/off speed (set at 30 and 35 MPH respectively) which turn the fans off above a certain speed as once you are moving and have airflow you really don't need the fans. From what I have read on the internet and the fine print in most of the tuning software this setting only relates to the A/C system commanding the fans, not the engine temp. If your engine temp is above the 'on' temp the fans will run regardless of speed. I believe this is why GM's 'on' temperatures seem a bit high when compared to the engine thermostat, this way you don't have the fans running while driving down the highway unable to get below the 'off' setpoint.
2. Set the type of fans fitted to the vehicle to "2 Fans" or whatever your tuning software calls this setting.
3. Change function of the Re-circulation Output on the PCM to "Fan #2" or whatever your tuning software calls this setting.
4. Under your idle airflow settings you need to include a small bump in g/s of airflow for when fan 1 and 2 start. I once again used the same numbers as a 2005+ truck. This will have your truck bump up the engine just a bit when the fans start to compensate for the load. If you don't, chances are that the computer will compensate for the load anyway, but this is right (OEM) way to do it.
4. Change the type of A/C system on the vehicle from "Analog Cycling" to "Analog". This is the part where we are stepping into uncharted territory a bit. I hope later in the post to get into why I selected this choice and why I believe it works, but for now let's just go on faith. Do note that depending on your tuning software this option may or may not exist. Based on my research HP Tuners and TunerCat OBDII (which is now sold under the JETS name or as part of a Roadrunner kit from Moates) both support this parameter. I was unable to find this setting anywhere in an EFI Live file, for those folks I assume you will have to do a segment flash of the System from a F-body and then attempt to configure everything back to a Truck with all the settings. I'm just guessing here based on my internet reading, I have no idea for sure, so good luck for you EFI Live guys.

My tuning software for this was TunerCat OBDII as I bought it years ago when it was the only tuning package for the 1998 trucks. Since then the licensing was sold out to JETS, but TunerCat is still providing updates. The TunerCat software interface leaves a bit to be desired compared to HP Tuners and EFI Live, but it seems to have all the tables of the big guys if not more, thus allowing me to make all the necessary changes. I used HP Tuners and EFI Live to review various Stock config files as part of my research into getting this all set up right.


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Old 08-09-2018, 04:08 PM
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Physical Installation:

Well, the fan relay harness I used was an OEM one from a 2005-2006 Suburban which fit right up like it belonged there just like the previously mentioned inspirational link. When routing the harness under the battery tray and along the bottom of the radiator the existing 1999-2002 split loom is too small to fit in the additional cooling fan wires. Also the clips which secure the split loom aren't able to take any larger split loom anyway so I just did like most people have done and zip tied my new fan wiring to the old wiring. Oh, I should point out that to keep the harness looking nice I sprung a couple dollars on Amazon for some "harness tape" this is a roll of approx 1" wide black PVC tape that doesn't have any adhesive. You use it to wrap the wires up nicely to keep them together and then secure the end with electrical tape. This is the same type of stuff the factory harnesses use and it results in a harness that isn't full of sticky electrical tape adhesive goo whenever you need to get back into the wiring. Well worth it. I don't think I need to go much more into the fan harness portion of the installation as it has been covered numerous times throughout the internet. My ultimate goal here was to make this harness installation as close to stock as possible. I even got the underhood fuse panel cover from a 2005-2006 truck as it has a little panel above the fan relays to allow access to the fuses and relays without having to remove the entire fuse panel cover.
As for the A/C high pressure sensor, the sensor will thread right on in place of the old switch. The port on the A/C system has a little schrader valve on it so all you get is a little puff of r135a when you remove the switch, no need to evacuate the A/C system. On the 2003+ trucks the sensor sits right next to the AC compressor and the wiring is part of the engine harness, on the 1999-2002 it is up by the radiator support and the wiring looks to be part of the body wiring. What I did find is that even with the different routing, the wire length turns out to be about the same so I didn't need to solder or crimp any PCM or sensor pins, just remove the wires from the junkyard harness and route them into my truck. I abandoned the old pressure switch wiring in place. I routed the new wiring from the sensor down to the harness running underneath the radiator (same harness the cooling fan routes along side). I wrapped these wires with the "harness tape" to keep them together, and since these wires were so small I was able tuck them into the existing split loom along the bottom of the radiator. When I got over by the battery tray it was kind of a bitch to fit this inside the existing loom so I just ran a chunk of new loom through there that had the fan wiring and A/C high pressure sensor wiring in it. Once I got up by the fuse box, I routed the sensor wiring and the two fan control wires over to the PCM doing the best I could to keep the wiring inside the split loom and wrapped up to keep it looking nice and together.
Get the 145A alternator. I put this on my truck years ago when putting electric fans on was the big thing. At the time the availability of the fans was limited and the prices were too rich for my blood. Still I was able to get the alternator for cheap back then so I started with that upgrade and never got any further (life and funds and such). You will need a slightly different length serpentine belt for the 145A unit as well. Don't cheap out here on the alternator, these fans draw 10A at stage 1 and a whopping 40+A at stage 2. The fans I have now are the older design where one fan is 5 blades and the other 7 blades. This is due to a mixup with the ebay vendor who was supposed to be sending the higher end ones which run 7 and 9 blades respectively. By my math the 5&7 blade units draw 500-600 Watts depending on what voltage you use to do the math, the 7&9 blade units are mentioned numerous times on the internet to be 700 Watts. I'm in discussions with the ebay vendor to either return these fans for the fancier ones or just discount what I have and call it good. The 5&7 blade units still move a lot of air.


Wiring Connections:

1. The Low Speed fan wire (Dark Green) was connected to C1-42.
2. The High Speed fan wire (Dark Blue) replaced the re-circulation pin in position C2-33. I just taped up the old pin and tucked it inside the factory harness.
3. The A/C high pressure sensor signal wire (Red/Black) connected to C2-14.
4. For the +5V sensor reference wire (Gray) you can't use the same pin as the F-body as that pin is occupied by the +5V feed to the fuel pressure sensor. After quite a bit of digging, I couldn't seem to come up with a spare +5V pin anywhere in the PCM. I could have just spliced my wiring onto another pin, but I didn't even know if this science experiment was going to work so I wanted something that was going to be easy to remove when it all went to crap. For this I chose to rob the +5V feed to the EGR (I removed my EGR years ago so these pins weren't feeding anything but a couple dangling wires anyway). The +5V signal for the EGR position is C1-48.
5. For the low reference signal wire (Black) I was in the same boat as the +5V reference, I couldn't find a damn spare pin anywhere. Once again, the EGR gave up his pin location for the greater good, this time it was position C1-23.


Final Comments:

I haven't had much time to do any exhaustive testing of the configuration so there is a possibility that there are other issues I have not discovered. Thus far all I have done is start the truck, fire up the A/C and make sure it causes the fans to come on. With the fans running on low with the A/C on full blast I disconnected the command to the fans for a little bit so the compressor would build up a bit of pressure on the high side and then plugged them back in. The computer ran the fans right to high speed and kept them there for the minimum on-time duration before dropping back to low speed. I scanned the truck with an old AutoTap I had laying around and it reported a value for the A/C high pressure sensor which seemed to vary depending on air flow. The AutoTap is kind of a piece of crap because it only displays the A/C high pressure sensor reading as 0-5v with no actual pressure scale, hell I can figure out that with a damn multimeter, but what else can you expect from 15+ year old software. The good news here is that the PCM reports a voltage number suggesting that it is taking in the sensor reading and using it to control the fans. I have not driven the truck nor have I even brought it up to operating temp since doing this install, however I do not anticipate any issues in that regard as that part of the installation is well proven territory.


Appendix:
A -- A/C Type Descriptions:

In the HP Tuners software under System->A/C there is a setting called Type Fitted. This setting configures the PCM for the type of A/C system being used. Based on my limited research these are the following settings and descriptions:

Serial - Used when the command to turn on the A/C compressor comes over the class 2 data bus and there is a A/C hihg pressure sensor being used. This is what the 2003+ trucks use.
Serial Cycling - Same as Serial except that a A/C high pressure switch is used.
Analog - This is what the F-body cars use (also various years of the Savannah vans). This is where the command to turn on the compressor comes from a hard wired PCM input and there is a A/C high pressure sensor being used.
Analog Cycling - This is what the 1999-2002 trucks use. This is where the command to turn on the compressor is hard wired to the PCM and there is a A/C high pressure switch used.
Passive - No idea WTF this is used for.
Not Fitted - Same here, no idea.

B -- Attached Schematics:

I have attached some of the GM schematics I have marked up to represent my installation. My truck has the automatic climate control, thus I used those schematics to document my work, but for this application the manual climate control differences are of no consequence.

Questions/comments? I'll try and answer what I can, but I am not on the forums much so I can't guarantee how good my followups will be. Also sorry for no pictures, never been much good at taking pictures to document my work.
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Old 08-09-2018, 04:08 PM
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Old 08-09-2018, 04:09 PM
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Old 08-10-2018, 05:01 PM
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Looks like a good resource, definitely going to watch for your results.

It almost sounds like you could take the EGR harness and extend it to the pressure sensor to tap into the reference voltage/ground. That might save running the pressure sensor harness around and moving/tapping into the EGR pins on PCM.

Once you get everything sorted maybe you could do an overview video, highlighting your harness routing and adding the switch, etc.
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Old 08-10-2018, 06:47 PM
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This is awesome info!! Back when I first did e-fans I despised the idea of the fans running when I'm going down the interstate at 70mph with the AC on and always on with the ac on regardless of whether it is needed. I also got an OEM harness, put in the larger rad, etc. Having read tons about 99% of aftermarket controllers failing I ended up getting two Dakota Digital parts to somewhat solve the issue. One of the devices connects to the OBD data lines, the other is their fan controller. The data box lets you control the speed at which the fans will not run, and lets you set the temperature points for low and high speed operation. The one I tried to wrap my head around was that other dang pressure sensor down low by the rad. I tried to find an appropriate trinary switch with the right pressure settings and never did find just what I wanted. Here I am several years later and doing so major work and wanting to revisit this and here you go and post a good working solution to get them working as OEM should. I also not have the full EFI Live kit so looks like I'm going to have to try and figure that end out is all.

I also never knew about the alternate fuse cover with the movable flap! I always thought it was sort of goofy that the relays and fuses are trapped under the cover requiring removal of the fender brace and removal of the entire fuse block cover to get to them. Any idea of the part number for the alternate cover? I need two..... also about to do this same to my Hummer H2 which is still on a clutch fan. Also just spotted a member here is making a custom cap for the front of the water pump. https://www.performancetrucks.net/fo...-plugs-552234/ I'm ordering two full sets.

Back when I did mine on the GMC I did get a new AC Delco 140A alternator and also went ahead and got the beefier fusible link (and then doubled that up with the original too). I also got the 5/7 blade fans for the GMC. When I did the process mine had the 28" rad so I got a new rad and went ahead and got a new overflow tank, flushed the cooling system, etc while I was at it. One last thing I did on the GMC is a added a 4 position rotary switch and extra wires to the relays so I'd have manual control if desired, or if the Dakota controller failed. That is "off (which disables them totally which might be good if fording deep water), auto, low, high". I've already ordered the new fans for my H2, I did get the 7/9 blade ones for that.

Anyways thanks for all of your well put info. I did a write up on mine way back then but I dont think many wanted to do to that effort.

Edit to add - any part numbers you might still have would be awesome! For me anyways I want to be sure of the underhood fuse box cover and possibly that harness for the pressure switch. Not too worried though. I found the pn for the switch in the docs you posted and found a pigtail for that connector I could use but I prefer OEM when possible.

Last edited by MixManSC; 08-10-2018 at 08:47 PM.
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Old 08-12-2018, 11:40 PM
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No idea on the part number for the cover. I just got mine in the junk yard. Didn't even know there was a different cover until I got to ripping all the parts out and saw the cover happened to have a second hole in it. Of course the rig I was ripping apart didn't have the lid for the cover, so I had to find another vehicle to raid for those parts.

So far the A/C setup seems to work fine. The A/C system hasn't had any need for the fans to run at high speed. I did go and play with it a little more tonight to make sure the A/C system is working as one would expect. Keep in mind I don't have the scanning software to actually know what the high side pressure actually is, all I can do is make wild *** gut assumptions. When doing this test it was a rather cool evening, I'd guess 70*F. So, here's what I did.
1. With the truck partially warmed up (thus the engine temp low enough it doesn't want the fans) I turned on the A/C full blast. The fans did NOT immediately start. It took probably 20 or so seconds for them to start. Given the ambient temps, I would suspect it took that long for the high side pressure to reach the low speed turn on set point.
2. For these ambient conditions the truck would have ran the A/C forever on low speed, so I had to kick it up a notch. I unplugged the little 2-wire connector that feeds the low and high speed command signals from the PCM to the fan harness (only really present if you got the complete OEM harness). Having this disconnected stopped the fans completely. I left this disconnected for probably 30-40 seconds while the A/C was blowing. During that time the A/C discharge temps in the truck remained cool. What should be happening during this time is that without any airflow over the condenser the high side system pressure should be climbing. After 30-40 seconds I re-connected this wiring allowing the fans to start running under whatever speed the PCM determined based on conditions. At this time the engine was close to operating temp, but still well below the high speed temp. When I reconnected the wiring the fans went right to high speed and stayed there for quite a while, around the minimum high speed run time set in the PCM.
Based on this, and short of having a scanner to read the actual high side pressure, I believe this is conclusive evidence that the A/C high pressure sensor is controlling the fans for both high and low speed.

What I do know from today is that my stomach is too soft for the factory temperature settings. High speed fan turn on isn't until 235*F!! So I took the advice of a colleague who has been doing some more tuning and brought all the fan set points down by 10*C. Now the high speed comes in at 217*F. That might be a bit too low now, but I don't like the temperature needle buried further over than what the clutch fan ran and the fans still just puttering along on low. On the plus side, the A/C system blew ice cold through the whole process.
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Old 08-14-2018, 09:53 AM
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Hopefully if I can get the time and get this sorted I'll have some more data. Working on mine very soon as I mentioned and I do also have a Tech2 which "should" allow me to monitor the temps and pressures exactly as the computers are reading them. I also have a full EFI Live setup so that will let me tweak things in the tune as needed. Hopefully I can get it all figured out. One thing I've not been able to locate online is the full harness for the trinary pressure switch but I can get a short pigtail for that which I'll have to extend.
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Old 08-14-2018, 10:08 AM
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I can't find the harness listed on their website anymore, but a month or so back these guys https://www.bp-automotive.com/ had a listing that included the pressure sensor and wire harness for it (sensor connector, length of wire, PCM pins, etc). I've also read good things about these guys, https://www.eficonnection.com/ maybe they can make you up the parts you need for a reasonable price.

One hangup you will run into with EFI Live is that they don't allow you to change the type of A/C system from the software. At least not that I can tell from looking around in the software. My understanding from what I have read is that you have to do a segment flash of the "system" section from a Camaro (which has the right A/C system) and then try and overwrite that with all of your "system" settings from your current config. The challenge here is that if there are "system" settings that differ between the Camaro and the Truck which EFI Live doesn't have mapped then you may not be able to set those things back to what you want leaving you with some non-functional configuration.
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Old 08-14-2018, 02:47 PM
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The A/C update kit from BP Auto is in the "Fan Harnesses" category on their website. https://www.bp-automotive.com/produc...ac-update-kit/
I had found their site before and didn't understand what that kit was for. Your post has put that info together now.

Definitely interested in what you find, as I have EFILive also. If you want to tap into the A/C sensor transducer, and monitor voltage via multimeter, you could probably create a formula to calculate the pressure, or even by logging the EGR voltage with HPtuners/EFILive/etc (if you have it through EGR) and then applying the formula, you may be able to tell.

I think EFI Live has the A/C High pressure PID you can log, but for 99-02, which didn't have the sensor it doesn't do anything. It may actually show data if you set it up right with the sensor installed.
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