sprigs
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Radiator fans Wiring diagram help
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 
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dennis the menace
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Re:Radiator fans Wiring diagram help
2012/10/21 13:26:17
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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.
Past-President, MR2 Owners Club Qld "There is a fine line between hobby and obsession."
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MIDN1T3
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Re:Radiator fans Wiring diagram help
2012/10/21 14:55:52
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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
1990 SW20 MR2 N/A with 1994 Gen 3 GTS 3S-GTE swap.
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robk
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Re:Radiator fans Wiring diagram help
2012/10/21 16:13:48
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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.
post edited by robk - 2012/10/21 16:58:57
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sprigs
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Re:Radiator fans Wiring diagram help
2012/10/21 21:04:08
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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.
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robk
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Re:Radiator fans Wiring diagram help
2012/10/21 22:33:52
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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!
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sprigs
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Re:Radiator fans Wiring diagram help
2012/10/23 01:17:14
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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.
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sprigs
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Re:Radiator fans Wiring diagram help
2012/10/27 21:38:43
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Apparently my a/c amp's internals have shorted, which means i need a new one.
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robk
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Re:Radiator fans Wiring diagram help
2012/10/27 22:24:33
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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!
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sprigs
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Re:Radiator fans Wiring diagram help
2012/10/27 23:00:46
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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.
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robk
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Re:Radiator fans Wiring diagram help
2012/10/28 01:26:19
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Oh, only $130, I thought it would be a lot more.
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cogs
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Re:Radiator fans Wiring diagram help
2012/10/28 02:20:48
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The A/C amp internals are all discrete components and it can be repaired. Mine was wrecked by an incompetent A/C mechanic trying to get a stupidly overgassed compressor to fire up by blindly pumping 12V into any connector that seemed A/C related. The fault ended up being a transistor connected to pin 10 that switches the no. 1 and 2 fan relays. A simple fix and 5 years later is still working. PM me for more info if you're interested.
BTW, the diode you mentioned is there to short out back-EMF from the relays (a high reverse voltage created when they de-energise) that would otherwise damage the transistor in the A/C amp. I think it's taped to the loom somewhere near the heater box. You don't need to find it to test it - with the relays and A/C pressure switch unplugged you can connect a diode tester to the coil connections on one of the relay plugs.
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sprigs
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Re:Radiator fans Wiring diagram help
2012/10/28 13:43:31
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robk - sorry the exact online saving price is $135.28, the msrp is $173.08 cogs - whoops 'shorted' was probably the wrong word to use more like fried! Behind the circuit board where those little black chips are, there's a small area there where a few of them are burnt out. I'll post up a pic when I can, dam battery went flat on the camera. Burnt out area is behind that circled resister.   
post edited by sprigs - 2012/10/28 15:35:59
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robk
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Re:Radiator fans Wiring diagram help
2012/10/28 16:45:11
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Where exactly is the A/C amplifier? Maybe I should pull mine out and have a look regardless of what else I check. All I know is it's under the dash somewhere.
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sprigs
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Re:Radiator fans Wiring diagram help
2012/10/28 18:59:17
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Not too sure myself but if i have to guess it just turns on/off diff parts of the air con system (inc rad fans) based on the signals it gets from the sensors/switches in the system. Its located on the passenger side, behind the heater bulk (sh!t a$$ location). Its attached to a bracket which is screwed onto the heater bulk, just unscrew the two screws, once you do that try to loosen it and disconnect the harness via feel because its quite tight down there. Once you get it out you can just unclip the top and slide the circuit board out. 
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