cooling fan modes and a/c
 

I have a 22 CX-5 with the 2.5 and about 3000 miles. I have noticed when idling with A/C on the RPMs fluctuate about every 8 seconds between 750 rpm and 500 rpm. I tracked it down to cycling of the radiator fan. The fan has two modes, low and high. When the RPMs drop to 500 I can hear a click and the radiator fan kicks up to high speed. After about 8 seconds it clicks again and RPMs return to 750ish as the fan returns to low speed. Is this normal operation of the system? I am used to cars going to high fan when the A/C is on and staying there. This seems like it would wear pretty hard cycling this much.

Everything these days is driven by trying to reduce fuel usage, so running the fan less often fits right in with that goal. Pulling a slight bit more juice to start the motor is gained back many times over during the period when it's not running.

AFA as the impact of more frequent start-ups of the motor, that would also be a trade-off against the reduced wear while the fan is off, and I'm sure that lots of lab analysis has been done in the past to determine exactly how that works out. And hopefully the manufacturer of these fans has been required to make whatever component choices are available to reduce wear as a result of the more frequent cycling. I guess time will tell on that.

Thank you for your response. So this behavior is normal? My main goal is making sure what mine is doing is indeed normal.

Yes, it's operating as designed.

I would at least have your battery load tested and perhaps if the service is free and also do a amp load test. The fans should NOT be consuming a load on the battery or your charging system enough to lower the RPM range on your model MAZDA unless there is a problem with the fans themselves or the ECU.

The MAZDA ECU will detect the extra voltage draw of the high-speed fan (alone) and increase the RPM NOT drop it.

I am not commenting on the AC compressor engagement and ECU Fan control but the fans alone.


Fans have multiple speeds depending on AC and other engine operation have been in ECU programs since at least 2000. Most fans do not have any difficulty in going it designed life span switching between low and high speed. The fan speed has a few functions other than simply the AC usage. IN the ECU there is a complex cycling program which is mainly set for temperatures of the engine, transmission and AC and even in some platform the ambient sensor input


Regarding performance calibration in the ECU I will often adjust the control ranges of the fan to personally fit the cars operating environment which is more custom and not universal as it came from the factory.