I have been using a SPAL fan-pwm v3 for a long time. I've been using the stock temperature sensor (the one that signals the ECU, not the one for the temperature gauge).
The problem I started having was sometimes the fan controller would get into some kind of error mode where the status LED would flash rapidly. I looked up the error codes in the FAN-PWM manual and there wasn't a code listed for this behavior (just rapidly flashing, no pauses between flashes).
I called Spal customer support and they told me that they were having problems with the software in the FAN-PWM so they removed the flashing of different error codes. My FAN-PWM was one of the newer models with the updated logic so that if there is ANY error (whether it's over-current, voltage too low, broken circuit with temp sensor, etc.) it will just flash the status LED rapidly, so there is no way for you to tell the different problems apart <img src="/forums/images/graemlins/angry.gif" alt="" />
I actually replaced the FAN-PWM thinking maybe it was bad, but the new unit has the same problem.
A couple times I didn't notice the LED flashing (didn't put it up high enough on the dash) and my engine started overheating. Scary, I could have killed my engine because of this problem.
I rewired everything and replaced the fan with a SPAL fan that draws less current. Problem still wasn't fixed. Checked the voltages supplying the unit, they don't seem too far out of spec. Only thing I can think of at this point is maybe the stock temperature sensor is sometimes flaky, which confuses the FAN-PWM making it throw an error, or else maybe the FAN-PWM unit gets too hot under the hood sometimes and goes into an error mode. Honestly though I am just guessing at this point. It is frustrating.
So, basically, long story short, this FAN-PWM works at least 95% of the time, but when it fails, it is dangerous as it can cause the engine to overheat while stopped in traffic if you don't notice it. If I notice the error code flashing, I can simply turn my engine off and back on again, then the FAN-PWM works fine! Crazy thing.
So since it is no longer 100% reliable, but works well MOST of the time, and I need this car to be reliable for my pregnant wife to sometimes drive, I came up with a failsafe system that would engage the fan in case the SPAL fails.
I ordered one of these, a SPAL temperature switch that turns on at 195 degrees and off at 175 degrees:http://www.jegs.com/i/SPAL/063/195TS/10002/-1
I will wire this up to a simple relay so that when this temperature switch kicks in, the relay switches.
Then I will splice the relay into my FAN-PWM wiring harness so that when the relay is NOT turned on, the fan is powered by the FAN-PWM unit. When the relay turns on, the circuit with the FAN-PWM is broken, and the fan will be powered straight off the battery (with a fuse inline).
This will bypass the FAN-PWM when the engine gets too hot and turn the fan on.
It blows my mind that the FAN-PWM wasn't designed to just run the fan anyway when it hits an error condition. It seems like that would be the logical failsafe they would program into the unit... If something goes wrong and you're flashing an error code and you don't know what to do, at least run the damn fan so the car can't overheat and destroy the engine!
Anyway, done ranting. I am going to wire it up this way, for now, but it's tempting to just strip out the FAN-PWM unit instead, and run ONLY off of this simple temperature switch. I could easily wire in an extra bypass to engage the fan when the AC compressor is on, too. The only thing I'd lose is that the FAN-PWM has programmable temperature thresholds, and can run the fan on "low" when it doesn't need to run full speed.
I used to think all that was nice but at the end of the day, the most important thing is that the damn fan better spin when the engine gets too hot.