You're right, darn it. Since the '96 model year, everything is supposed to be standardized among all manufacturers of cars sold in the U.S. I looked it up in the Chrysler service manual and you have the correct description.
Now that we're in the same circuit, understand that it is physically impossible for a relay to overheat, ... Except for one uncommon condition. The coil that activates the movable contact is designed to run on 14 volts which is system voltage when the alternator is running and charging the battery. The only way that coil can overheat is if it is partially shorted already. We can eliminate that because you already replaced the relay.
The second and more common cause of overheating is resistance in the circuit. Just like water flowing in a garden hose, there is a pressure drop at any restriction, as long as water is flowing. Voltage is electrical pressure. Resistance is that restriction. The goal is to have no resistance anywhere in the circuit except for the load which is the fan motor. If the contacts in the relay are burned or pitted there will be a little resistance between them. That resistance drops a little of that 14 volts so not all of it appears at the motor. The important part is when there is voltage, (lets say 1 volt), dropped across the contacts, and there is current flowing THROUGH the contacts, there is power dissipated at them. Voltage times current equals power which is heat. Heat buildup in the contacts promotes more burning which increases resistance and causes even more heat buildup. It's a vicious cycle. The cure can involve sanding the contacts clean and smooth but obviously replacing the relay will also take care of that problem.
But, ... Along with that, there's one thing you didn't change and is just as likely to cause the problem. That is burned terminals on the relay where they plug into the socket. Look at the old relay's terminals to see if two of them are blackened. If they are, replace the terminals in the socket too. Squeeze them a little tighter if necessary so they make a solid connection.
A tight fan motor will slow down and draw higher current which will aggravate the condition. Partially shorted windings in the motor will also cause an increase in current even though the fan spins freely. Now that you have a new motor installed, the current flow might be down to normal, but overheated relay terminals will still cause trouble and continue to get worse.
If by some chance you don't find overheated terminals, something else has to be drawing heavy current if the new relay continues to get hot. I can walk you through a test procedure to measure the current, but I've never had to do it myself so I don't know what a normal value is. The motor is protected by a 30 amp fuse, so taking the safety margin into account, I'd expect to see around 20 amps. To test it you'll need an ammeter that can measure at least up to 20 amps DC.
Friday, June 3rd, 2011 AT 4:16 AM
