How loud is the A/C radiator fan supposed to be?

Is the fan on the passenger side behind the radiator typically loud?

Background...

Yesterday I thought it was time to check up on our 2007 Prius's A/C, as it has been hot lately and best to detect if these are going out well before they fail completely. On entering the car its internal temperature was 102F (it had been sitting in the sun with the windows all down an inch), the outside air temperature was 91F (both on the climate control and with the instant read thermometer in the shade) and the National Weather site said humidity was 41% at the nearest station. Stuck the thermometer in the right center vent, set A/C to "Max Cool" and Recirculate, medium blower speed, and went for a drive. After a short time (2 minutes? didn't time it) the thermometer dropped down to 46F, and then it wandered around in the 46-48F range, probably depending on speed, angle of the sun, and other variables. More than 40F below ambient, so "OK" function by that common measure, although I suppose it could have been lower. After a while pulled over and stopped in the shade, put it in Park with the parking brake on and let it continue to run. Air temperature (on the dash) still read 91F and the vent dropped into the 44.6-45.1F range, which is 2-3F lower than in the sun. Cabin temperature was measured in the shade with the thermometer, and was 73F. That's OK for me, a little hot for my wife. It was probably hotter while driving but I didn't think to measure it then.

Here's the thing, after a short time (30 seconds?) in the shade it sounded like the motor had restarted, but the dash didn't show that. So I took a look under the hood and the noise seemed to be coming from the fan behind the radiator(s) on the passenger side. It didn't sound like a fan in distress (no scraping, rattling or bearing sounds), just a loud fan (as if moving a lot of air). Never noticed that sound before, but in retrospect, it might have accounted for some of the times I thought the motor was running but it wasn't showing up on the MFD. If there was a fan on the driver's side it was either whisper quiet or not running. I'm pretty sure it was the fan and not the compressor (same general area) as the compressor was presumably running the whole time, and once that fan started it didn't stop until the car was moving.

Can Techstream turn on each of the front fans separately? If yes next time we get a cool day I will see if they are both that loud.

 

Interesting. The sound seemed to be coming from the passenger side, not equally from both sides. I guess the driver's side fan might be out. I usually test fans in a situation like this (hard to see) by gently poking them with the dangling end of a zip tie. If they both make the same frequency ticking noise then they are moving at the same speed, even if one fan is louder than the other for some other reason. No ticking, well, dead fan. I would expect the Prius would throw a code if one of the fans was out, but maybe not.