Radiator fan always on, won't turn off unless unplug battery

If your talking about coolant temp sensor, maybe something wrong with sensor? Any applicable trouble codes? Some of the national brand auto stores will check codes for free.

Some makes and models if you unplug that sensor, there will be a default mode and the computer will turn on radiator fan. If you turn on ac, the fan may run.

It could be a leak, check your radiator for any leaks, also check upper and lower radiator hoses, water pump, etc. But you said the fan doesn't kick on even when it's reading "hot". So I would look into that more. route the wires and locate the plug, make sure it's plugged in, or reseat the cable by unplugging, and replugging it back in. You could also unplug the negative cable on the battery terminal for a few seconds in attempt to reset the ECU (computer).

check the fuse and the relay ,, unplug the fan, and use a jumper to the battery to make sure the fan is working, if it is,, then its going to be a bad fuse or relay

The first thing I would check would be the temperature sensor that sends a signal to the relay to turn the fan on. Of course make sure you have plenty of water in the radiator or the sensor won't work at all. I have seen anti-freeze come through the sensor and corrode the wires shorting them out. So it could be broken wires, unplugged wires or a bad sensor. I am not sure exactly where the sensor is at on the Pacifica but your local parts store could show you. It is usually in the intake or cylinder head.

you need a new radiator fan relay, under $50 at rockauto.com

So youre saying the fans are coming on and going off like they should, have you changed your thermostat and be sure to burp the system getting out all the air bubbles. And the check engine light will not always go out on its own, most times manually clearing it or disconnecting the battery is the only to go if you dont have a generic scan tool

I would presume you are meaning an electric fan that has two fans together. Both fans dont always run at the same time. One is a high speed fan and the other a low speed fan together in the same shroud. Engine temp determines if and when they turn on. *****CAUTION!!!!! Fans can turn on any time the key is in the on position even if the engine isnt running. Do not put your finger in the fan or handle them unless the Neg (-) battery terminal is disconnected.*****

Removal & Installation

1. Disconnect the negative battery cable.
   
2. Drain the engine coolant into a suitable container.
   
3. If necessary for access, remove the air cleaner, mounting stud and duct.
   
4. Remove the upper fan mounting bolts.
   

On some vehicles, such as this 1998 model, remove the upper fan mounting bolts

1. Unfasten the retainers, then remove the upper radiator panel.
   

Unfasten the upper radiator panel fasteners, then remove the panel

CAUTION When draining the coolant, keep in mind that cats and dogs are attracted by ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old. To avoid being burned, do NOT remove the thermostat housing cap while the engine is at normal operating temperature. The cooling system will release scalding fluid and steam under pressure if the cap is removed while the engine is still hot.

1. Remove the cooling fans, as outlined later in this section.
   
2. Disconnect the coolant reservoir hose from the radiator neck and the radiator hoses from the radiator.
   

Unfasten the hose clamp and disconnect the coolant reservoir hose from the radiator neck


Disconnect the remaining hoses from the radiator

1. If equipped, unplug the cooling sending unit electrical connector.
   

On some vehicles, you must unplug the coolant sending unit electrical connector

1. If equipped, disconnect the engine oil cooler lines from the radiator.
   
2. If equipped with an automatic transaxle, disconnect the transaxle cooler lines from the radiator side tank.
   

Use a flare nut wrench to disconnect the upper transaxle oil cooler line

Well the first thing I can tell you is that the radiator fan should kick on as soon as you turn on the a/c. That's because of the extra strain it puts on the engine. So, if you don't see or hear the fan go on with the a/c, it's probably dead. You could also unplug the fan and run a jumper wire off of the battery to see if it goes on.

The radiator cooling fan(s) -- correct?

This sounds like the radiator-fan thermal switch is stuck or the wire going to it is grounded.

To stop it, find the switch (somewhere in/around the radiator) unplug the wire, tape the end of the wire, tuck it away somewhere.

To fix it will probably require a mechanic unless you have the experience.