Got a quick question for the experts. What capacity does my ECM have......say for controlling electric fans? Found some harnesses that have the ECM wires for 2 stage fan control. What bin files are there to be turned on? Thank you in advance!


Randy

 

Not exactly answering the question you asked, but here's some experience (from several vehicles, including some close relatives to the blazer).

In my experience, the mechanical fan does fine for engine cooling, provided your fan clutch is working correctly. I always change the fan clutch with the waterpump on the 4.3 (or on Vortec V8's in GM products).

Sometimes, the stock fan is insufficient for the AC in city traffic. I've added an electric fan (pusher fan) on the front of the AC condenser to address that issue. On anything like a Blazer (Chevrolet S10, full sized pickup, and especially in F body cars with lots of glass and not much radiator or AC evaporator), I just used a single stage, high capacity fan wired with a relay to the AC switch, or to the compressor clutch wiring. On other applications (not GM), I've used a two speed fan, wired the "low" position to a relay with a coolant temp switch added to the intake manifold or radiator plumbing, and the "high" speed wiring controlled by a relay with the Air Conditioning.

 

My take on this is while wheeling in the southern heat(Texas) with A/C on and moving slow the electrics would be better choice over the clutch fan. Yes on road in traffic it will be a giant leap over the clutch fan. Just need to find out if the 95 ECM can control the electrics. Will be asking this on another section for EFI if some there would know.

 

My gut feeling is that the PCM on these vehicles doesn't have outputs to control an electric fan. I looked in GM's parts catalog, and the 1996 PCM fits about twenty different models, each with somewhere between three and ten different trim and engine variants. The one thing every vehicle it fits has in common is that they were equipped from the factory with an engine driven fan with a thermo/mechanical fan clutch. The number of models and variants in 1999 is smaller, but again, none were equipped with electric fans. This PCM fits 4.3L V6 as well as small block and big block gas powered V8's up to the K3500 4WD pickups with the 7.4L (454) gas V8.

I've had a couple decades experience in Florida, southern Georgia and north Georgia (including the metro Atlanta area). I know a little about hot, humid weather. With only two exceptions, every vehicle (of any kind) which was equipped from the factory with an engine driven, mechanical fan, but was "retrofitted" with electric fans and came in with overheating issues to a shop or dealership where I worked either left with the factory fan, clutch and shroud, operating as designed and no overheating issues, or those vehicles left with the retrofitted electric fans, still overheating in stop and go traffic.

If you go with an electric fan, you want to keep the stock fan shroud, and you need a fan that fills the opening in the shroud, has enough volume to match the stock fan blades. The only two I ever got to work were designed as pusher fans, but I installed them with the electric motor between the fan blades and the radiator core. The fan blades completely filled the opening in the stock shroud, and the electric motor was in the same space occupied by the stock fan clutch. You might be able make some custom bracketry for the radiator and shroud in these vehicles to do that, and get an appropriate fan, but it would be expensive (you need way more fan than you think for stop and go traffic), and you'd have to add sensors and relays to control it.

In my experience, unshrouded electric fans will always overheat in stop and go traffic. Poorly shrouded electric fans will always overheat in stop and go traffic.

If the vehicle is overheating with the stock system, repairing the issue with the stock system will always resolve the overheating.

Adding a condenser fan in front of the AC condenser can help an undersized R134 system (R12-R134 conversion, or 1990s era stock R134 system). With the addition of a fan pushing from the front of the condenser, you typically get another 5 to 10 degrees cooler inside the vehicle with the air conditioning in hot weather. BTW, Mercedes-Benz S class sedans had an engine driven mechanical fan for engine cooling with an additional electric fan on the AC condenser from 1979 into the late 1990's. That system is proven and works very well.

Oh, and in case you were thinking anything from the Buick 3800 V6 (also a 90° V6 with some ties to V8 engines) would work, that engine was EDIS (Electronic Distributorless Ignition System) in 1996, and used completely different sensors and wiring. The PCM and PCM connectors are completely different for that engine.

 

I agree, if electric fans were better, all vehicles would have them. With latitudinal engine orientation, you're forced to use electric fans, not because they're better, they are not. Another unintended consequence with front wheel drive. We all found out, at a very early age, that front wheel drive sucks... remember your first tricycle? As Racer_X mentioned, if the factory cooling system is working properly, the engine will not overheat.

 

Being that I'm not a spring chicken.....57 years old....some electric fans are just plain garbage! Yes to both of your answers.....stock clutch fans work exceptionally well. I was station in Florida in the late 70's and early 80's and had all kinds of engine driven fans on every car I owned. They have work well but.......slow and labored driving they don't work as well since that is not what they were designed to do. I'll take the advice and install a new clutch and add a pusher in front of the A/C condenser. I'll see how that works this summer in 100F+ temps we get here while moving slow and laboring the engine while wheeling some trails. Thank you all for your sound advice. Great dialog on this question.

Randy S. Hager
Venus, TX