newtonf57

Hey Everyone,

New to the site here and I'm hoping you can help me out. I have used the site for a lot of information during this swap but this is the first post.

Let me first say I'm not at all a novice to wiring or electrical but this one's got me blowing steam. Here's the nonsense I'm dealing with.

1991 Camaro w/ 2003 Tahoe 5.3; 700r4; Full gut of stock wiring from the Firewall connector forward; self performed harness rework and custom fuse/relay block.

Fan 2 is enabled in the PCM under both the fans and A/C Recirc section. Relay control functions properly at set temps and when commanded via HP Tuners.Everything works flawlessly with this swap except for the electric fans.

Symptoms: Fan 1 and Fan 2 will both blow their separate 30A fuses when the PCM trips the corresponding relay, but ONLY if the engine is running when they are turned on....

Tests performed so far:
Fan (1 or 2) direct to battery feed - Runs, no issues
Fan (1 or 2) turned on via HP Tuners, Engine Off - Runs, no issues
Fan (1 or 2) turned on via HP Tuners, Engine ON with Alternator control wire disconnected - Runs, no issues - With fan running at this point, plug Alternator control wire in, system voltage comes up, fan speeds up, does not blow fuse.
Fan (1 or 2) turned on via HP Tuners, Engine ON with alternator control plugged in - Blows fuse immediately
System voltage with engine running is 14.20 volts, so I'm not over powering the system.
I have quadruple checked every wire from the custom fuse block I made all the way to the fans - no issues found. No rubs on the insulation, no shorts, no anything.
Multi-Meter reading *AC* voltage at the back of the Alternator is reading 27.9 volts with the engine OFF and 30.1 volts with the engine ON. So I have about 2.2 volts of AC Power sneaking through, likely a weakening diode in the rectifier circuit, but not enough to cause the symptoms in my opinion. (Why it reads 27.9 with the engine OFF I have no clue other than the battery may be low in the Multi-Meter)

Fans are both Derale 18212 with Amp Draw specs of High Speed 21, Low Speed 15. Both fans are wired for High Speed only and the instructions recommend a 30 amp fuse.

I should be pulling 21 amps through a 30 amp fuse on a 35 amp relay and everything should be fine.

Verbal Relay Schematic:
Pin 85 - PCM (-) Trigger
Pin 86 - Key (+)
Pin 87 - Battery (+)
Pin 87a - Not Used
Pin 30 - Fan Fuse (1 or 2 respectively)
Fan Fuse the goes straight to its respective fan

Can anyone advise on what I seem to be missing??????????

Spartan7

iTrader: (7)

I imagine you're probably popping the fuses from the initial current draw when the fans come on. Try a 40A fuse temporarily and see if it solves the issue, or put a meter in series that can handle the current and see what it's pulling.

My second thought would be a bad voltage regulator in the alternator that is allowing a higher than normal spike on engine startup.

newtonf57

I had thought the same thing about the initial current draw but ruled that out because they will fire and run fine if the engine is off. So the 30 amp fuse is clearly holding the kick of them starting. I will give it a shot with a 40 just to see.

​​​​​​it is doing it after the engine has been running and warmed up, not on initial engine start. And like I said, the voltage is reading 14.20 steady so I feel like the regulator is functioning properly.

RockinWs6

Use a analog or digital logging meter to log the voltage when the fuses blow.

newtonf57

Voltage goes from 14.2 to 14.1 for a split second as it blows the fuse. Have not been able to get a 40 in there yet to see if it holds it.

wssix99

iTrader: (5)

I'm thinking this must be a short or wiring problem with a device that is energized only when the engine is running. If there was a problem with the fan, the fuse, etc. it would express itself at any and every time. (Supply voltage would not make a difference.)

newtonf57

I agree but why would it not blow with the engine running and alternator unplugged?? You would think that would pinpoint the alternator as the issue but its obviously charging with a system voltage of 14.2 so it can't be shorting anything. And I think if it was the alternator it would have blown when the fan was running and I plugged the alternator back in but it didn't, it just sped the fan up when the system voltage raised from the charging system.

fastassls1maro

iTrader: (22)

i would try a 40amp fuse just to see. Its possible its only blowing the fuses after its been running due to the warmer temps in the engine bay causing a higher resistance on initial startup.

newtonf57

I'm gonna pick up some 40s or some 30 amp slo-blows and see if that alleviates it. Should know in a couple of hours.

1 FMF

iTrader: (1)

multi-meter AC voltage reading - disregard this, you cannot use a sub $x00 multi meter in this fashion to determine AC ripple voltage. It does not work that way.

If you have time and a few bucks rig up an inline fuse and power each and only each fan directly from battery with a 30, 25, 20, 15 amp fuse to determine what the inrush current might be, when you stop blowing a fuse then you have reasonably ball parked that value. once the fan is running you can use a multi meter on DC amperage connected inline or in series to measure current draw of the fan.

you guys seems to suggest if the alternator has system voltage higher that the fans would be drawing more current. That is not true. The fan electric motor {once running under constant load} will consume a given wattage (of power). W = volts * amps.
At battery voltage of 12.6 volts, going by numbers in first post it seems like a fan draws around 250 watts at high speed = 21 amps. At 13 volts the fan would draw 19.2 amps, at 14.5 volts 17.2 amps. The alternator could have system voltage at 16 or 17 volts and the fans should work just fine- you'd have other problems before you had problems with the fans, so i would discontinue any effort troubleshooting the alternator unless you have a check engine light and DTC related to it even if it has 1 or 2 failed diodes and there is an AC ripple voltage in the system.

my guess without seeing it first hand is you have an incorrect relay or have it installed wrong or wired wrong. GM runs the oem fans using 3 relays and the PCM grounds either 1 or both relays to operate the two electric fans, both relays grounded = high speed where each fan sees full power on its + wire, and both fans' ground wires in the electrical sense go to ground but it's not a direct connection to ground!

just 1 relay grounded results in the ground wire from one fan passing through a relay and becomes the power wire to the second fan or on low speed, then the fan 2 ground wire goes to ground resulting in the fans running in series which gives you low speed fan operation. I suspect it is here that is causing your problem, a relay is switching a fan hot wire that you think is going to the fan but you are switching it to ground causing a direct short.

I've attached a pic of the oem wiring of the fans for the LS1 1998-2002.
is the wiring for a 2003 tahoe 5.3L different? I don't know, I assume it is not.

i have the 2002 GM service manual, and don't quote me on this but i thought i remember reading somewhere that if high speed fan operation is desired that the pcm does not ground both wires to the relays simultaneously. i thought i remember it does 1 wire first for only a second or two to get both fans going low speed then grounds both wires for high speed, was something to do with reducing initial current draw which would cause a brief system voltage drop and they do this to prevent that. this would be in the pcm programming that i don't think you can change. so even though you have stuff wired for high speed only, what might be happening is the grounding of just 1 relay is putting a power wire to ground that you don't think is happening - you would need to tie together wires from pin 33 and 42 dark blue and dark green together to prevent this, and doing so will cause a DTC related to the radiator fans in the pcm. or disconnect pin 33 dark blue from pcm and manually wire that middle relay dark blue wire to ground instead of going to pcm to force an always high speed fan condition - this is if you are still wired close to oem diagram.

newtonf57

The OEM diagram is completely outnof play here due to the fact that the 03 Tahoe ran a mechanical fan only and had zero provisions for the electric fan. I had to add the wires to the pcm connector for fan 1 and 2 relay trip. When I say both fans are wired for high speed I simply mean that my aftermarket fans are capable of high and low or just high speed wiring. I have the fans wired so that they are high speed as soon as they are fed power. I just took low speed out of play on the fan end of things.

The fans are already independently fused at 30 amps each. I'm not trying to run both through a single 30 amp fuse.

I picked up some 14 ga fusable link and I'm going to try that instead as it would be capable of handling a higher surge amperage as the fans kick on.

I agree with your statement on the amperage being less at a higher voltage. Wattage is the constant, and amperage and voltage are the direct and opossite reacting variables. What I am wondering is, will the fans have a higher SURGE amperage at the higher voltage because the fan motor is going to be "reacting" harder to the inrush of 14.2 volts as opposed to 12.6.

RockinWs6

You have a analog meter or a logging digital meter. You won't be able to see the split second voltage rise on a regular digital vom. Its possible the voltage is going sky high causing a huge current inrush blowing the fuses. Are the fuses time delay or slow blow etc?

If you are blowing 30amp fuses you should be able to se something unusual on the volt meter. Also read the voltage at the fuses! not at the battery etc. Example if there is a short in the circuit and you are logging the voltage at the fuse see a huge voltage drop as the 30 amp fuse blows. If the voltage goes high as the fuse blow then you are drawing high current.

Again a regular VOM is useless to see these voltages. till the VOM responds the event is over.

newtonf57

Its a logging digital meter. Voltage going from 14.2 to 14.1 was at the fuse.

For the time being I have bypassed the fuses and am running straight from relay to fan. They are functioning 100% this way.

I am running ATM fuses and cannot get a 40 locally. I am going to install the 14ga fusible link tomorrow evening and make sure they still work. If they do, I'll run them like that permanently. I don't see any reason that wouldn't be protection enough considering the relays have a 120amp breaker in front of them as well that's running the whole fuse block assembly I made. Thoughts?

newtonf57

The 30s were not slo-blows. I forgot to answer that in the last post.

RockinWs6

........................

RockinWs6

OF COURSE IT WILL BE HIGHER IF THE VOLTAGE IS HIGHER!


Before you try to help someone, Someone needs to help you!


THE HIGHER THE VOLTAGE THE HIGHER THE CURRENT, please disregard 1 FMF

newtonf57

I appreciate your help WS6, but before you call someone out, you might want to make sure you're right. See attached. It's basic ohms law calculations. Enter voltage and wattage and resistance and amperage are automatically calculated.

RockinWs6

Look I know this is the net and everyone chimes in but listen carefully. If the motor draws 10 amps at 12 volts at 24 it will draw 20amps!

1 FMF

iTrader: (1)

http://www.electricaleasy.com/2014/0...-dc-motor.html

so depending on the actual type of electric motor in your Derale 18212 fans,
if the armature of the motor (i.e. fan blades) are stalled then technically yes a higher input voltage to the motor would result in higher current draw on first startup. Once the motor is spinning then current draw is reduced, and it's anyone's guess as to how the manufacturer accounts for this difference in their published numbers. It's been a while since i messed with DC motors but like article describes there's a starting circuit in most to limit inrush current, if these motors are cheap being auto aftermarket they may have no such circuit which is to stay if you physically held the fan blades stationary and fed the motor power it would be a simple I=V/R calculation and a continually higher than expected current and the motor would burn up since it expects to start rotating immediately.
I suppose, ballparking motor resistance at 0.5 ohm, that at a rated 12.0 volts it would be 24 amps, and real world at 14.5 volts it would be 29 amps.
you would need to get an accurate measurement of the electric motor resistance, and that of your electrical system. I suppose it might just be enough, if armature resistance is lower than 0.5 ohms and electrical system could be higher than you think- if you measure 14.2 volts at battery terminals but alternator could be putting out 14.6 volts at its terminal to make up for voltage drop in the system and you are seeing closer to that 14.6 volts versus 14.2 at radiator fan.

also my point of oem control starting fans in series on low speed, inherently reducing inrush current, tends to favor my memory of why they do it... because they use a less expensive DC electric motor not having any kind of starting circuit... and the 1 OEM fuse for powering both fans was 40A expecting the two fans to start in series.

1 FMF

iTrader: (1)

yes you are correct regarding his fan motors, I struck out my text above.
I was looking at it wrong, thinking power consumed would not change but for a fan motor such as this it would - higher voltage resulting in higher current and faster spinning fan.