1990 Corolla radiator fan constantly running

I have just purchased a 1990 corolla dx, 94k miles. It is the 4 door sedan model with automatic trans. I have 14 years experience as a full-time auto mechanic. However, this electrical fan problem is eating my lunch as electrical problems in general are not my 'cup of tea'.

Shortly after buying the car, I drove it and realized it had an overheating problem. I thought "It should be easy to fix" - haha ! :Mrgreen: Anyways, here's the scoop on it so far.

The coolant wasn't circulating. So, I threw in a new t-stat. Still, no circulation. So I diagnosed the radiator with a partial blockage. So, I threw in a new radiator. Then, plenty of circulation. But, it was still overheating.

The radiator cooling fan wasn't coming on. I powered it up manually to the bat. And it was bad; so I replaced it with another used fan from a similar corolla. (Not sure what year because my coworker grabbed it from a junkyard-bound corolla for me before it went to the junkyard).

New fan motors for these cars are approx. $100 aftermarket and much more from toyota as you know. I'm trying to save as much money as possible - the radiator and t-stat (as well as other parts such as wheel cyls, brake pads, cv boots, etc. Are starting to add up) and cost me more money than I anticipated to get the car drivable. Money I don't have.

Anyways, now the overheating problem is gone. But, both fans (a/c condenser fan and the radiator fan) run non-stop. As soon as I switch the ignition key to 'on' -without even starting the car, both fans come on. After starting, they stay on. They don't shut off until. The key is switched to 'off' This happens when the vehicle is cold and sitting all night or after it has been driven. It makes no difference.

As I know this is a problem and the fans will eventually burn out - just like the original one did from running continuously. I took a look at the wiring circuit and it shows 3 relays, a radiator fan switch, a/c high press switch and so on. I went to the wrecking yard and found all 3 relays which were good and swapped them with the ones on my car - no change. I replaced the radiator fan switch - no change.

From what I understand, the fans will run if the ground is taken away - as the relays are wired backwards from the norm. They are wired normally closed through the a/c switch and rad. Fan switch. When either of these switches open, the fans are supposed to turn on. However, both of these switches are closed and the fans are still running? :

Any suggestions as what to check- much appreciated in advance.
Sunday, July 9th, 2006 AT 2:54 PM

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Update :

I believe that I overlooked the a/c pressure switch. When I jumped across the switch - the fans stopped. Off to get another switch. I don't know why I didn't try that before - that's why I don't do much electrical work :mrgreen: :lol:
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Sunday, July 9th, 2006 AT 4:17 PM

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