I'm trying to trouble shoot my radiator fans that get turned on as soon as I turn the key to the ON position and stay on. Relays have been tested and work.
Looking at the wiring diagram I kind of stumped at what the diode does (just above the circled pressure switch). And where abouts is it located so I can go check it out. I've already checked under the fuse box and its not there.
My car has A/C

My first port of call is the water temp sensor, on the side of the radiator.  If this has failed, or if the connector is off, the fans come on and stay on.  A fail safe situation, I guess.

Hi Sprigs,
 
I had the same problem (and I think a few other people on here as well).  The problem was to do with the A/C circuit which occurred when I got my A/C fixed as auto-electric guys had wired something incorrectly which provided power to the fans all the time - I can't actually remember which part of the circuit, i'm thinking the A/C amplifier?
 
I'll check my receipts and let you know.
 

dennis the menace

My first port of call is the water temp sensor, on the side of the radiator.  If this has failed, or if the connector is off, the fans come on and stay on.  A fail safe situation, I guess.

sprigs

I'm trying to trouble shoot my radiator fans that get turned on as soon as I turn the key to the ON position and stay on. Relays have been tested and work.
Looking at the wiring diagram I kind of stumped at what the diode does (just above the circled pressure switch). And where abouts is it located so I can go check it out. I've already checked under the fuse box and its not there.
My car has A/C

I have exactly the same problem, ie. thermofans running full speed at all times when the ignition is on.
I too have checked all the relevant relays and found no problem, but I haven't checked anything else. It could be a problem with any one or more of the following:
- the diode you mentioned (maybe)
- the A/C amplifier
- the sensor/switch in the radiator
- the A/C pressure switch

I don't know where the diode is, or the A/C pressure switch, so let me know if you find those.
 
I'm keen to hear of any further progress you make! The last time I looked into it (testing the relays) was about a year ago, and I haven't bothered to look at it since then.

hmm currently my car is fitted with the radiator from a wreck I purchased to fix my car which happened to have no A/C. Turns out they use diff senors/switches depending on whether the car is equipped with a/c. So installing the proper sensor might fix this.

Robk - the pressure switch is located just behind the power steering fluid reservoir.

sprigs
hmm currently my car is fitted with the radiator from a wreck I purchased to fix my car which happened to have no A/C. Turns out they use diff senors/switches depending on whether the car is equipped with a/c. So installing the proper sensor might fix this.

If you're talking about the thing in the radiator, I guess that would explain why it is sometimes referred to as a switch and sometimes referred to as a sensor.
Do you know the relevant part numbers?
 

sprigs
Robk - the pressure switch is located just behind the power steering fluid reservoir.

Thanks!

I only know the part number for the sensor that goes into the radiator (88625‑17011) and it costs about $50+shipping from lithia toyota parts, quite expensive though and it may not even fix the problem if i decide to get it.
Well read up something interesting supposedly the a/c and non-a/c cars are wired up the same except that the non-a/c car had a bypass plug attached where the amp or pressure switch is. I might give that ago since I'm currently using the non-a/c sensor/switch but I lose my a/c in the process if I get it to work, I do remember my dad testing the pressure switch plug, that plug has 4 pins and he bridged two of them and got it to run in low speed. Theres no info on that pressure switch plug and the 93 bgb shows a 2 pin (wtf?) but hopefully I have something there.

Apparently my a/c amp's internals have shorted, which means i need a new one.

Hmmm, that sucks, that's probably the most expensive of all the parts that could cause the problem. At least that explains the problem for you though!

yeh sucks bad according to lithia toyota the amp cost $130+shipping, i guess i could just do w/o air con, till i find a second hand one.