2005 Prius Radiator Fan does not go into high speed

1. Was the car in a front-end collision prior to your noticing this issue?
2. If so, check the direction of the air flow when the fans are blowing. Is air blowing towards the engine (which is correct) or towards the front grille (which is incorrect)?
3. Both fans should turn on when the air conditioner compressor is running. If the compressor is not running, then one fan should turn on once the engine coolant reaches a sufficiently high temperature. That is based upon readings from the engine coolant sensor located in the cylinder head, which provides engine coolant temp info to the engine ECU.
4. Consult techinfo.toyota.com to obtain the electrical wiring diagram so you can see how the engine ECU and air conditioner amplifier control the two fan motor speeds.

 

how are you determining fan speed?

 

If you consult the electrical wiring diagram, you will see that there are three fan control relays, named Fan #1, Fan #2, and Fan #3.

1. In order for the two fans to run at a slow speed (where the two fans are connected in series from 12VDC to ground), Fan #3 is activated while Relays #1 and #2 remain open. Since the two fans will operate at slow speed, it appears that Fan #3 is good.

2. Shorting the radiator temp sensor will activate Fan #3, so both fans should operate at slow speed.

3. In order to get Fan #1 and Fan #2 to activate (where each fan will be connected from 12VDC to ground, hence will operate at high speed), one of three things has to happen:

a) the pressure switch on the air conditioner refrigerant line has to turn on
b) the air conditioner amplifier has to activate the two fans
c) the engine control module has to decide the engine coolant is hot enough to warrant the fans running at high speed

4. Check the 30A RDI fuse by removing the fuse and using an ohmmeter to verify continuity.

5. If that fuse is good, remove Fan #1 and Fan #2 relays. Make the Prius READY and turn the air conditioner on. The two fans should not run since the two relays are removed. Short the terminals 3 to 5 which are the switched terminals on Fan #1 relay to see if one fan will run at full speed. Then, remove the short and short the terminals 3 to 5 on Fan #2 relay to see if the other fan will run at full speed. Remove the short, then short terminals 3 to 4 on Fan #2 to confirm that both fans run at slow speed.

With either relay, make sure you do not short terminals 1 and 2 together, which are the relay coil terminals. Use an ohmmeter on the relay to identify the coil terminals vs. the switched terminals. The coil terminals will measure ~100 ohms or thereabouts.

6. If you can get both fans to run at full speed by shorting the relay terminals, then there may be something wrong with the junction connection between the two relays and the wires that provide connections for the three items 3a, 3b, and 3c.

7. If you cannot get the fans to run at full speed then there is some obscure problem with the relay wiring. Hopefully you won't need to get this far.

 

P1 pressure swish is at the AC sight glass.

Turn AC to max cold with high fan speed and then unplug it.

If the fan speed drops fans were already at full speed (and that switch is OK). Don’t leave it like this for long.

If the fan speed didn’t change. Then either you have bad swish, or pressure just wasn’t high enough to need full fan speed, or you have some other electrical problem. Then you can bridge the two wires in this connector. If fan speed now increases you have bad swish, or pressure just wasn’t high enough to need full fan speed. If it still doesn’t increase you have some other electrical fault.

 

I didn’t realize pressure switch has double function. Unplugging it will turn the AC off because of the low pressure switch that is connected to pins 1 and 4.

Connect the pins 2 and 3 colors light green and white with black stripe and you should get the fans to full speed. It shouldn’t really matter which white with black stripe you connect the light green wire. Disconnect the connector and bridge them from the front side. If you then get the full speed, that you haven’t gotten when you should, you just need new pressure switch.

If you didn’t get fans running by bridging, disconnect the 12V battery for 10min or so to clear the codes you caused. And then we can get back to trying to find problem with wiring, relay, or fuse. Or if you decide to get it to somewhere they don’t get confused by those codes.

 

I actually think that switch connected to pins 1 and 4 is a low pressure switch as well as a high pressure switch. So if the refrigerant is either under- or over-charged, the circuit will open.

I agree that it would be a good test to try bridging the wiring harness connector to see what happens with the radiator fan speed. If that pressure switch turns out to be the problem, the OP needs to have the switch replaced by his local Toyota dealer or an independent competent to work on the Toyota hybrid air conditioning system - since the refrigerant will need to be removed from the system prior to the switch being unscrewed.

 

You will need place that has equipment for high voltage hybrid AC. Independent hybrid specialist or Toyota dealer will probably be the best option.

 

Shouldn't the switch be tested based on the pressure in the system? Based on the above comments, it seems like the OP might be about to replace a switch he doesn't need to. What if the high side pressure isn't high enough for the switch to turn the fans on to high?

Avi

 

Now, I have some questions:

1. Has anyone ever messed with the refrigerant?
2. How was the fact that the refrigerant level is correct determined?
3. What was the high side pressure at when the switch was tested?

Thanks,

Avi

 

The OP says the AC "works great" when the car is moving, which implies that the refrigerant level is reasonable. However, as you suggested, it would not hurt to have the low and high side pressures measured before the switch is actually replaced, to verify that the switch is the problem vs. insufficient refrigerant charge.

 

Is it really that hard to find a shop that knows how to fix the A/C on a Prius in Los Angeles?

 

Fault in Radiator fan (not condenser fan) or short in wiring. But if the fuse was blown jumping the pressure switch wires should only make condenser fan run at full speed, radiator fan wouldn’t run at all.

 

It is hard to tell the difference. He might have heard only the condenser fan run at high speed and thought it was both fans. The only time I've had to replace those was when a fan motor was defective. I've seen them still work but draw too much current. Usually the car was in an accident and had the fan hit the radiator.