That’s how I did my 02. It’s been fine for years.
Electric Fan Conversion Question
- Thread starter Dantheman-2003
- Start date
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You won’t be able to do it exactly the same as the 05-up because your wiring harness isn’t the same. Do the best you can and don’t stress over it is my suggestion unless you want to find an 05 harness for the entire front end of your truck and take forever to switch it over and hope everything still works afterwards.
Tonyrodz
Resident Resident
What would happen if you disconnect the ac compressor during the cold months? Then it wouldn't trigger the fan to come on once the defroster was turned on. When I was younger I used to unplug the compressor during the cold months with no drawbacks.
ScottyBoy
Full Access Member
In most climates, it would be just fine. But in very humid climates, like here in Louisiana, the AC compressor comes on to help the defroster to decrease humidity, and it that actually helps a LOT. But in drier climates, you will most likely not see any issue.
Another option would be to wire in an toggle switch on the AC trigger wire on that fan relay. Turn it off in cold weather, but then you will have to remember to turn it back on in warmer weather. I just left mine alone, and the only real drawback I've noticed is that sometimes in colder weather (belowe freezing) my truck takes a LOT longer to warm up.
Matthew Jeschke
Full Access Member
@ScottyBoy makes perfect sense about the AC Compressor clutch. If I have to tear apart the AC system again I'll add that pressure sensor maybe lol
My friend has a 2005 Silverado. I asked him if I could look under his hood and he didn't even give me an answer. He kind of looked at me weird
My friend has a 2005 Silverado. I asked him if I could look under his hood and he didn't even give me an answer. He kind of looked at me weird
ScottyBoy
Full Access Member
I remember reading in a thread over on Performance Trucks about adding a pressure sensor and then reconfigure the computer software to recognize it and everything. So it can allegedly be done, but in my opinion it's not worth the hassle. Like I said, I have been daily driving my 2001 like this since 2010, so that's 15 years now and it's been doing perfectly fine except for VERY cold days, which honestly doesn't even happen that often in Louisiana. And with you being in Arizona, I'm guessing you would not have very many sub-freezing days as well. The ONLY difference between the harness you have and a completely stock harness in a 2005 is the AC trigger. Yours is now triggered by the AC clutch wire, (so anytime the AC compressor is enagaged, one fan wil be on) and a 2005 is triggered by the ECM, and the ECM triggers it when it senses the AC pressures are above a certain threshold. Both harnesses are triggered exactly the same as far as the temperature. When the ECM senses that the coolant temperature is above a certain threshold, it triggers both fans to come on at low speed. But if one fan is already on because of the AC, then the other fan will turn on at high speed, therefore having both fans on at high speed. When the AC is off and the coolant gets up to temperature, both fans are wired in series, so they come on at low speed.@ScottyBoy makes perfect sense about the AC Compressor clutch. If I have to tear apart the AC system again I'll add that pressure sensor maybe lol
My friend has a 2005 Silverado. I asked him if I could look under his hood and he didn't even give me an answer. He kind of looked at me weird
Also, if you haven't already upgrades your alternator, I highly suggest that you upgrade to a more powerful alternator. I upgraded from a 130a to a 145a, and I still sometimes see a sharp voltage drop for a second when the fans kick on. But that usually only happens at idle. At higher engine rpm's, I don't notice any voltage fluctuations. I also added a smaller alternator pulley to help the alternator spin faster, which helped marginally but not a lot. I bought it on Ebay for like $15 shipped, so at that price it was worth it l guess.
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Matthew Jeschke
Full Access Member
I got everything wired up... @ScottyBoy Did you intend the AC clutch signal wire be fed through the supply / power side of the relay to the compressor clutch? I hooked it to the control / trigger wire for clutch relay and it doesn't work... Otherwise I can short the relay and the fans go on.
I can also command the fans on from the PCM (although not individually, as I see only the low temp fan is wired up in harness). I just cannot command on the fans when the AC turns on.
BEEN UPDATING MY NOTES AND SAVING THEM HERE AS I FIGURE THIS OUT.
Studying schematics for the 2005 Tahoe. I think I may have a less expensive way to do this...
The pressure sensor is a voltage divider. It's giving a fraction of 5V proportional to the pressure. Not sure what the impedance of the sensor is, but probably doesn't matter. I'll try a 100k ohm potentiometer
PCM Pinout
C1 pin 45 (Gray) is the 5V reference (Supply voltage)
C2 Pin 14 (Red/Black) is the signal being read (divided voltage)
C2 Pin 80 (Black) is the reference ground
I can connect a potentiometer in there and figure out which voltage commands on the fans. Only thing is, I'm not 100% sure but assume the PCM looks at the AC clutch being commanded ON AND not JUST the pressure. Otherwise, we're back to needing a relay.
If this works a couple cheap resistors can be used in lieu of the relay... additionally, I'm assuming you only used the low temp fan trigger from PCM as you had to splice the two fan relay triggers together to use the relay method w/ AC clutch.
Found sensor on Rock Auto. It's a three pin confirming schematic above. I think those wires are dedicated to just that sensor (the reference power is not shared with any other sensors?).
I hooked up a pot to spare PCM in my lab and it worked as I'd thought. Additionally, given HPT looks like the PCM does discern Pressure sensor from AC clutch command signal. Tomorrow I can try it in the vehicle with the potentiometer.
I'm guessing 50% divider say two 50kohm resistors (2.5v) will work fine but don't have the scalar / multiplier for voltage to PSI on the sensor.
This webpage says 0V is 0PSI and 5V is roughly 430PSI.
Stock settings for pressure AC refrigerant pressure command on in PCM from 2005 chevy tahoe.
DTC0530 Less than 100mV or greater than 4.9v for 5 seconds trips code.
This indicates the divider may have a resolution of 2%... 1:500
It'd be nice to have one of the sensors available to measure impedance.
PCM PINOUT 2005 versus 2001 Tahoe:
5V Reference
C1 pin 45 (Gray) 2005 5V reference (Supply voltage) for AC pressure
C1 pin 45 (Gray) 2001 Fuel Tank Pressure sensor
C1 Pin 46 (Gray) 2005 Fuel Tank Pressure 5V reference
C1 Pin 46 (Gray) 2001 Throttle Position Sensor 5V reference
SIGNAL
C2 Pin 14 (Red/Black) 2001 UNPOPULATED
C2 Pin 14 (Red/Black) 2005 is the signal being read (divided voltage)
REFERENCE GROUND:
C2 Pin 80 (Black) 2005 Reference Ground AC Pressure
C2 Pin 80 (Black) 2001 Fuel Tank Pressure Sensor
C2 Pin 64 (Dark Green) 2005 Fuel Tank Pressure Sensor
C2 Pin 64 (Dark Green) 2001 Fuel Tank Pressure Sensor
I need to find out if low reference and 5v reference lines have to be paired. Not sure if they're isolating those lines to reduce noise (is what I'd do if I designed the PCM).
It does appear as though they do splice the reference lines though. Not ideal but really probably not to big an issue.
I can also command the fans on from the PCM (although not individually, as I see only the low temp fan is wired up in harness). I just cannot command on the fans when the AC turns on.
BEEN UPDATING MY NOTES AND SAVING THEM HERE AS I FIGURE THIS OUT.
Studying schematics for the 2005 Tahoe. I think I may have a less expensive way to do this...
The pressure sensor is a voltage divider. It's giving a fraction of 5V proportional to the pressure. Not sure what the impedance of the sensor is, but probably doesn't matter. I'll try a 100k ohm potentiometer
PCM Pinout
C1 pin 45 (Gray) is the 5V reference (Supply voltage)
C2 Pin 14 (Red/Black) is the signal being read (divided voltage)
C2 Pin 80 (Black) is the reference ground
I can connect a potentiometer in there and figure out which voltage commands on the fans. Only thing is, I'm not 100% sure but assume the PCM looks at the AC clutch being commanded ON AND not JUST the pressure. Otherwise, we're back to needing a relay.
If this works a couple cheap resistors can be used in lieu of the relay... additionally, I'm assuming you only used the low temp fan trigger from PCM as you had to splice the two fan relay triggers together to use the relay method w/ AC clutch.
Found sensor on Rock Auto. It's a three pin confirming schematic above. I think those wires are dedicated to just that sensor (the reference power is not shared with any other sensors?).
I hooked up a pot to spare PCM in my lab and it worked as I'd thought. Additionally, given HPT looks like the PCM does discern Pressure sensor from AC clutch command signal. Tomorrow I can try it in the vehicle with the potentiometer.
I'm guessing 50% divider say two 50kohm resistors (2.5v) will work fine but don't have the scalar / multiplier for voltage to PSI on the sensor.
This webpage says 0V is 0PSI and 5V is roughly 430PSI.
A/C Pressure Sensor Function
How do automotive A/C refrigerant pressure sensors work? How to test A/C refrigerant pressure sensors.
www.freeasestudyguides.com
Stock settings for pressure AC refrigerant pressure command on in PCM from 2005 chevy tahoe.
DTC0530 Less than 100mV or greater than 4.9v for 5 seconds trips code.
This indicates the divider may have a resolution of 2%... 1:500
It'd be nice to have one of the sensors available to measure impedance.
PCM PINOUT 2005 versus 2001 Tahoe:
5V Reference
C1 pin 45 (Gray) 2005 5V reference (Supply voltage) for AC pressure
C1 pin 45 (Gray) 2001 Fuel Tank Pressure sensor
C1 Pin 46 (Gray) 2005 Fuel Tank Pressure 5V reference
C1 Pin 46 (Gray) 2001 Throttle Position Sensor 5V reference
SIGNAL
C2 Pin 14 (Red/Black) 2001 UNPOPULATED
C2 Pin 14 (Red/Black) 2005 is the signal being read (divided voltage)
REFERENCE GROUND:
C2 Pin 80 (Black) 2005 Reference Ground AC Pressure
C2 Pin 80 (Black) 2001 Fuel Tank Pressure Sensor
C2 Pin 64 (Dark Green) 2005 Fuel Tank Pressure Sensor
C2 Pin 64 (Dark Green) 2001 Fuel Tank Pressure Sensor
I need to find out if low reference and 5v reference lines have to be paired. Not sure if they're isolating those lines to reduce noise (is what I'd do if I designed the PCM).
It does appear as though they do splice the reference lines though. Not ideal but really probably not to big an issue.
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Matthew Jeschke
Full Access Member
After some study the low speed and high speed fans is fairly simple in concept. Low speed connects fans in series (voltage divides proportionally to motor load / size).
High speed switches the ground connection order (middle relay), establishes a connection to positive voltage (fan right) Coolant Fan Relay 2 (left)... This reconfigures the motors to be in parallel, each receiving full alternator voltage.
I'm going to try and rig this up so there's no low and high speed mode. I drive off road in extreme heat and definitely need the high speed mode. Right now as configured the harness works but only uses high speed when AC is turned on.
Unfortunately, I cannot reconfigure the PCM to accommodate the high speed pin. It's pin is populated with something else on the 2001 Tahoe.
I'm not sure how to do this w/ risking blowing up my PCM... as the trigger wire for the AC clutch relay is in the harness from @ScottyBoy is tapped onto the supply line for the AC clutch fused at around 140Watts. On a side note, maybe worth trying to put a resistor in series with the relay in harness to limit current on that line. Could be dumping a fair amount of current through the coil on the relay (typically the relays like 250mA if that, I've not measured draw with relay in parallels to AC clutch power). If I splice that into the same line as the trigger wire for the Low speed fan from PCM then I created a ground path from much more powerful circuit (AC clutch circuit) through the PCM which could easily fry it.
I may just delete the AC clutch relay all together... AC won't cool as well till engine is up to temp but should work fine / not hurt anything. Then splice blue 473 to 335 D-green above so I get full fan power when fans are commanded on instead of only when AC is commanded on.
Another thought is a thermostat switch. I could just put a thermostat switch on the radiator for say 215F and splice that into the high speed relay.
This is a bit jankier than I'd hoped for unfortunately.
Studying differences between 2005 Tahoe and 2001 in HPT.
If I compare the PCM harnesses C1 and C2 the correlate with the terminology above. I think what happens if if you change these settings it reconfigures those pins and executes the logic for the pressure sensor.
My 2001 Tahoe
The 2005 Tahoe
I went out and loaded up a tune with the "Recirculation Fitted" set to Fan #2... I think I had some success! When using the scanner I commanded Fan #2 on and the recirculation door moved! This tells me that you can get control of Fan 2 from my 2001 Tahoe. However, it may require sacrificing "recirculation" functionality of HVAC and or coupling the fan and the recirculation door.
2005 C2 Pin 33 High speed Fan mode
2001 C2 Pin 33 Recirculation Actuator Control
Beyond that there appears to be a bit more to the recirculation mode I maybe sacrificing if I switch that setting. I'm not sure what C2 Pin 11 "High pressure recirculation switch" is about.. is that the defog / defrost function of the AC?
I can also of course command on fan one and the fans turn on (low speed).
Analog Cycling is a AC that operates on discrete (on / off) pressure switches to control the pressure in the line set.
Serial Cycling is an AC that operates off of specific high side pressure to control pressure in line set.
Pretty sure I cannot get away with changing the one setting to Serial Cycling so getting the PCM to control the fans off line pressure probably not happening. Maybe more grief than worth it to convert the signals of analog to be compatible with serial cycling controller paradigm.
RANTING... Why on earth did they EVER design this PCM with AC controls in the engine controller. *Facepalm* got to be the dumbest thing I've ever seen other than perhaps controlling cooling fans which double as condenser fans. GM could have done this WAY easier with a discrete line to the PCM to request fans on or even some wizardry on the fan relay trigger, maybe I a serial communication but that seems like overkill.
High speed switches the ground connection order (middle relay), establishes a connection to positive voltage (fan right) Coolant Fan Relay 2 (left)... This reconfigures the motors to be in parallel, each receiving full alternator voltage.
I'm going to try and rig this up so there's no low and high speed mode. I drive off road in extreme heat and definitely need the high speed mode. Right now as configured the harness works but only uses high speed when AC is turned on.
Unfortunately, I cannot reconfigure the PCM to accommodate the high speed pin. It's pin is populated with something else on the 2001 Tahoe.
I'm not sure how to do this w/ risking blowing up my PCM... as the trigger wire for the AC clutch relay is in the harness from @ScottyBoy is tapped onto the supply line for the AC clutch fused at around 140Watts. On a side note, maybe worth trying to put a resistor in series with the relay in harness to limit current on that line. Could be dumping a fair amount of current through the coil on the relay (typically the relays like 250mA if that, I've not measured draw with relay in parallels to AC clutch power). If I splice that into the same line as the trigger wire for the Low speed fan from PCM then I created a ground path from much more powerful circuit (AC clutch circuit) through the PCM which could easily fry it.
I may just delete the AC clutch relay all together... AC won't cool as well till engine is up to temp but should work fine / not hurt anything. Then splice blue 473 to 335 D-green above so I get full fan power when fans are commanded on instead of only when AC is commanded on.
Another thought is a thermostat switch. I could just put a thermostat switch on the radiator for say 215F and splice that into the high speed relay.
This is a bit jankier than I'd hoped for unfortunately.
Studying differences between 2005 Tahoe and 2001 in HPT.
If I compare the PCM harnesses C1 and C2 the correlate with the terminology above. I think what happens if if you change these settings it reconfigures those pins and executes the logic for the pressure sensor.
My 2001 Tahoe
The 2005 Tahoe
I went out and loaded up a tune with the "Recirculation Fitted" set to Fan #2... I think I had some success! When using the scanner I commanded Fan #2 on and the recirculation door moved! This tells me that you can get control of Fan 2 from my 2001 Tahoe. However, it may require sacrificing "recirculation" functionality of HVAC and or coupling the fan and the recirculation door.
2005 C2 Pin 33 High speed Fan mode
2001 C2 Pin 33 Recirculation Actuator Control
Beyond that there appears to be a bit more to the recirculation mode I maybe sacrificing if I switch that setting. I'm not sure what C2 Pin 11 "High pressure recirculation switch" is about.. is that the defog / defrost function of the AC?
I can also of course command on fan one and the fans turn on (low speed).
Analog Cycling is a AC that operates on discrete (on / off) pressure switches to control the pressure in the line set.
Serial Cycling is an AC that operates off of specific high side pressure to control pressure in line set.
Pretty sure I cannot get away with changing the one setting to Serial Cycling so getting the PCM to control the fans off line pressure probably not happening. Maybe more grief than worth it to convert the signals of analog to be compatible with serial cycling controller paradigm.
RANTING... Why on earth did they EVER design this PCM with AC controls in the engine controller. *Facepalm* got to be the dumbest thing I've ever seen other than perhaps controlling cooling fans which double as condenser fans. GM could have done this WAY easier with a discrete line to the PCM to request fans on or even some wizardry on the fan relay trigger, maybe I a serial communication but that seems like overkill.
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ScottyBoy
Full Access Member
You are WAY overthinking all of this. Are you really willing to sacrifice you AC circulation function JUST to have the PCM trigger the fans, and not the AC compressor trigger the fans?
Yes, the temp relay commands them on at low speed. But low speed is more than enough to cool just fine in most situations. Thats how GM designed it to function, and it's been working just fine on every GM truck since 2005 that came with electric fans. You only need high speed when it's warm or hot outside. And of COURSE if it's over 75 or 80 degrees you will have your AC running. The AC compressor will trigger them to run at HIGH speed. I have been daily driving my truck with it wired like this 2010 or 2011 and it's been working just fine. And trust me, these brutal Louisiana summers are NO joke. It gets pretty hot down here, regularly in the triple digits in July and August. And my fans have performed flawlessly and kept my truck cool and my AC blowing cold. EVERY single harness I have sold with an extra relay spliced in for the AC compressor clutch wire has worked the same way. Others like Rocketman and everyone else with a 00-02 can confirm that their fans work the same way and they work perfectly fine like this. If the AC pressures are high enough to trigger the fans on a 2005, then the compressor WILL be running. Thats why it's FAR easier to just tie into the compressor clutch with on a 00-02 trucks instead of a ton of extra wiring and programming to get it to work.
But if you really want all the headaches of completely rewiring your truck to have the computer trigger the fans, instead of the AC triggering the fans, then go for it. Let us know how it all turns out in case anyone else wants to end up doing all of that.
Yes, the temp relay commands them on at low speed. But low speed is more than enough to cool just fine in most situations. Thats how GM designed it to function, and it's been working just fine on every GM truck since 2005 that came with electric fans. You only need high speed when it's warm or hot outside. And of COURSE if it's over 75 or 80 degrees you will have your AC running. The AC compressor will trigger them to run at HIGH speed. I have been daily driving my truck with it wired like this 2010 or 2011 and it's been working just fine. And trust me, these brutal Louisiana summers are NO joke. It gets pretty hot down here, regularly in the triple digits in July and August. And my fans have performed flawlessly and kept my truck cool and my AC blowing cold. EVERY single harness I have sold with an extra relay spliced in for the AC compressor clutch wire has worked the same way. Others like Rocketman and everyone else with a 00-02 can confirm that their fans work the same way and they work perfectly fine like this. If the AC pressures are high enough to trigger the fans on a 2005, then the compressor WILL be running. Thats why it's FAR easier to just tie into the compressor clutch with on a 00-02 trucks instead of a ton of extra wiring and programming to get it to work.
But if you really want all the headaches of completely rewiring your truck to have the computer trigger the fans, instead of the AC triggering the fans, then go for it. Let us know how it all turns out in case anyone else wants to end up doing all of that.
THIS^^^^^
