Hey guys,
I have a 89 Integra that has a cooling fan problem. The engine gets close to overheating at idle and the fan never comes on but gets cooler as you start driving. I tested the fan by connecting it directly to the battery and it runs fine that way. From what I've read so far, (please correct me if I'm wrong) the Coolant Temperature Sending Unit sends the signal to the Cooling Fan Relay to turn it on? Is the sending unit the one with one wire or two wires? Also there are three relays next to the radiator, how do I tell which one is the fan relay and how do I test it? The system has been bled to make sure there is no air in the system. Thanks for your guys help in advance.

 

Anyone reading, here's what I've found so far:

The two sensors I mentioned in the post are as follows:

1. Coolant Temperature Sending Unit - One Wire - sends temperature info the the gauge cluster - simple test is to see if the gauge is working in the cluster, going the right direction and not showing its cooling down when it should be warming up.

2. Coolant Temperature Sensor - Two wires - sends info to ECM for engine management - Simple test is to check the resistance across the two terminals on the sensor using a digital multimeter, first with Engine cold and then after about two minutes of running it. Switch the multimeter to 2000 or 20k reading. The resistance with it cold should be around 2000 ohms and after two minutes of running it it should be significantly low, approximately around 700-800 ohms, lesser is good too. Here's are some links where I got some of this info:
http://www.topbuzz.co.uk/maintenance/cts/cts.htm
http://www.wonderhowto.com/how-to/vi...nsor-267190_2/

Also, another way to check, given that your car runs fine and the only problem you have is overheating due to fan not coming on, is to unplug the sensor connector and try to start the car. It will either not start or start very poorly. Well as long as it does that you know the sensor was working and sending info to ECM to keep the engine running. DO NOT run the engine without it for more than 3-5 seconds. Its a simple test to confirm that the sensor when plugged in does its job.

So this rules out both the sending unit and the CTS. Now back to the relay part. I've got three clustered together next to the radiator, need to figure out which one is the radiator fan relay. Thanks in advance for any help you can provide.