I'm blowing Fan #2 and Fan #3 relay. Got any ideas on what's causing it?

I guess it's possible to shorted motor like for a fan or something could burn up a relay That's what the relays for I think is to protect the motor and the device from a short or what have you or a direct short to ground or something like that The relay won't kick in or it'll kick in and burn up I would tend to take the old relays that I took out and replaced first the blue ones or whatever color they are from the Toyota and if you look carefully you can pull that top off the relay flip it over look at the pins you'll see the little stake points The new ones are plastic You can just pry them with the plastic spluges slide the top off Do you see any burnt issues of the original relays that you replaced at AutoZone and just because you plugged them in and they worked doesn't make them correct there is a diagram on top of the relay plastic that shows the pin out and the markings and what actually goes on with the relay It is possible they weren't actually bad they might be doing their job You put in a relay that wasn't exactly right from someplace that sells auto parts and it put the fan on doesn't mean the fan is necessarily good or any of that I've seen this happen before I am not an all-out electrical guy so I don't make these switches lightly. Given the fact that you had them working for a couple of days I remember your original post and now they're not working again I would be looking for the original relays and if I didn't have them I would go to another car that I can take them out of not just keep buying more relays from places I would want to get the originals that I know belong in the car and they are plentiful and they don't have to be new because these are very rare to go bad actually I don't think I've ever replaced a set on a generation 2 Prius at all the relays for the fans or the ABS or any other relays so in my world I would want to find out why the relays are believed or I'm being led to believe are bad and if I had the originals I could open them up and see any funny business anything turning blue overheating whatever. But yes bad motors like a fan motor it's remotely possible it could suck a relay dry and lock it up if it was failing heavily definitely something you want to check of course if the fan motor was failing that heavily I would expect to see smoke excessive heat possibly noise coming from the offending electric motor.

 

Yes but not YOU personally.
Given your admitted lack of knowledge here,
I suggest that a shop visit would be in order.

A fan drawing high current might cause that.
A fan that is jammed and not turning might cause it too.
YOU should be able to check them for free movement......with everything OFF of course.

Note: Your car is almost 20 years old.
How much longer do you think it will be cost effective to keep it ??

 

I would take the relays out and test them, before jumping to any conclusions about "blowing" them.

Relays aren't there to 'protect' stuff, that's what fuses are for. The only job of the relays is to turn the fans on and off when the controls say to.

The coil in a relay is unlikely to 'blow'; it's made to see a full 12 V across it whenever the car wants it on. It's perfectly happy that way.

The contacts in a relay can get pitted or stuck together, maybe faster if a short in the motor circuit draws high current, but you'd expect to notice that blowing a fuse. There are fuses, and those are there to protect stuff.

I would look for something else going on in the circuit.

 

Would AutoZone Menards or O'Reilly's. Even have the right relays that we're talking about? He just walked in and got handed two more I don't even know if he has the original and the fan started working. To be honest with you I don't think I've ever replaced a relay in a factory Toyota setup since I've been driving Toyotas since I don't know 70 something like that I have swapped them out from another car to another car but usually the relay had nothing to do with anything It was just to see usually as a bad motor or component or something like that not a bad relay. I mean there's a lot of manufacturers that make fans for the aftermarket must be a reason for it I guess they do go bad

 

In some circuits (speaking in general terms) there are capacitors attaching the switched contacts on the relay. Resistance elsewhere in the circuit combined with that capacitor creates an RC time constant so that the voltage goes up (or down) slowly. If such a capacitor failed it might result in pitted or fused conductors in the switch, and short lifetimes for replaced relays. That said, I have no idea if that method is used anywhere in a Prius.

Here is a video demonstrating the concept:

 

Why does Tom type like that? LOL

 

Maybe Sam can ask to make this a sticky to advise all 2004 Prius owners.

 

Yes when your person sitting in the driver seat ready is the car turns the AC on preferably not an auto mode put it on low put it on high fan recirculate air conditioner light lit up but not necessarily an auto compressor running you verified by touching the compressor whatever hearing it and at the same time all that commotion started you should now feel air coming from the fans blowing onto your hand that should be sitting in front of your air box about 4 in below it The place where you put in your air filter If you can't feel air blowing across your hand you have a problem You need to find out why The fans shouldn't be running slow or any of that nonsense they should be running what I would call full tilt and you should hear that fan noise It will sound like a box fan that you normally stand on the floor or in the window of your house if you ever done such a thing sounds like air moving with two of those fans working and they're about 12 in 14 in in diameter so they're no slouches but when they start to go bad they start to not spin it speed not moving much air and not cooling the gas and so your compressor is pumping hot uncooled gas trying to get it ready to do its thing and make cold again well it doesn't do such a good job when it's hot.

 

Pretty sure he's not typing, just using speech-to-text and never fixing anything.

 

BINGO.

I think somebody mentioned that earlier.

 

It is not funny.
It is because he is lazy and inconsiderate.
Try the "ignore" function.

 

Fans that won't move at all are either seized (at the motor) or wedged (at the blades). If the former usually all you can do is replace it. If the latter you may be able to find whatever is jamming it and pull it out. Visibility into these fans is pretty poor when they are in their normal operating position, to look for an obstruction either a mirror on a stick or an inspection camera with a flexible probe will be needed. Even with those the obstruction could be hidden within the fan guard. If you come to the conclusion that the fan is toast, and cannot see the obstruction, try forcing the blade to move by tapping it forward or backward in the direction it should spin. (In such a way that there is no possibility of punching a hole in the radiator!) With luck that could break the obstruction free and the fan could spin again. Without luck the blade will break. It is true that if the fan was removed and inspected you might be able to see the obstruction with it out of the car, but if you have already gone to that much work it would make more sense to put in a new one anyway, given the age of the failed one.

There are a couple of videos on youtube showing Prius fan replacements. It doesn't look like a lot of fun as there isn't enough clearance to just pull it off with the radiator in place. People either tilt the radiator towards the front of the car or remove it to make enough space to get the fan out.

 

There's all kinds of ways to skin that fan cat spax and Hayden I'll have options for most any car that had an electric fan or you can just go grab a used off of the like similar car at the junkyard I'm not sure what the pancake motors cost from Toyota new or if you can buy them that way whether you have to buy the whole fan assembly or you can buy the motor and the impeller separately just depends on Toyota itself. Usually when my fans go bad I use the two brands mentioned above because then I'm replacing a whole fan assembly and all of that I usually remove the shroud and the bracket and strap the fan right to the radiator but some people don't like to do that so there's that.

 

Yes. The system is designed so that BOTH turn on at the same time. Initially they should turn on low speed when you select A/C (fairly quiet). If needed, both should turn on high (fairly loud) when engine temperature gets hot enough.

If one fan is seized then the cooling system can't work properly. Period.

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