Engine fan

There is no specfic switch to turn the fans on. The coolant temperature sensor is an input to the PCM, and the PCM is responsible for fan operation. When you have A/C on, are the fans running at all? They should be on any time the compressor is on.

What kind of temperature are you expecting them to come on? From memory, it should be around 212 to 220 minimum for low speed operation.

Do you have heat coming out of the vents(heater). The question is, is the coolant temperature sensor seeing the high temperature? I am not sure if you can view it, some years had it and some did not, the coolant temperature on the information center. If it does not, it may be view-able in on-board vehicle diagnostics. I would have to do some research to find the data parameter to direct you to. Do you have a good concentration of coolant in the system, as well as a pressure cap? Understand that I am asking you these questions in order to determine if you have a cooling fan concern, or a cooling system concern.

I will give you the description and operation of the cooling fans from the service manual. Typically, there are few concern with cooling fans, especially if they can be brought on with A/C request.

Description and operation:

The Powertrain Control Module (PCM) controls both cooling fans by controlling three relays through two outputs. There are two modes of cooling fan operation: low speed and high speed. In the low speed mode, the cooling fans are powered in series. The PCM energizes Cooling Fan 1 Relay causing both cooling fans to run at low speed. In the high speed mode the cooling fans are powered in parallel which runs the fans at high speed. The PCM energizes all three cooling fan relays during high-speed mode.

Low Speed Conditions
The PCM turns on the cooling fans at low speed when the engine coolant temperature exceeds 106 °C (223 °F). The cooling fans turn off when the engine coolant temperature falls below 102 °C (216 °F). The PCM monitors engine coolant temperature using the engine coolant temperature sensor input on YEL (410).

The PCM also activates low speed operation if the transaxle temperature exceeds 150 °C (302 °F). The cooling fans turn off when the transaxle temperature falls below 110 °C (230 °F). The PCM monitors transaxle temperature using the transaxle temperature sensor input on YEL/BLK (1227). (Refer to Engine Controls ). See: Powertrain ManagementComputers and Control SystemsDescription and Operation

The Heater and A/C Programmer requests the PCM to turn on the cooling fans at low speed through the Class II data line when the A/C high side refrigerant temperature exceeds 50 °C (122 °F). The programmer requests that the cooling fans turn off once the A/C high side refrigerant temperature falls below 47 °C (117 °F).

The PCM turns on the cooling fans at low speed if a low coolant level is detected and the engine coolant temperature exceeds 80 °C (180 °F). The cooling fans turn off when the engine coolant temperature drops below 76 °C (169 °F).

Low Speed Operation
Low speed cooling fan operation occurs when the PCM grounds the Cooling Fan 1 Relay coil on CKT 335. With only Cooling Fan 1 Relay energized, voltage is applied to both the LH and RH Cooling Fan Motors. Power is supplied to the motors through the Cooling Fan 1 Relay contacts circuits. BLK (532), WHT (504) and LT BLU (409), and the Cooling Fan 2 Relay contacts. The two motors are connected through a series circuit. This circuit divides the voltage applied by COOL FNS Maxi  Fuse between the two motors. The division of the voltage causes the motors to operate at a lower speed. In the series mode, the fans are grounded through BLK (350) and ground G107.

High Speed Conditions
The PCM turns on the cooling fans at high speed when the engine coolant temperature exceeds 112 °C (234 °F) or the Engine Coolant Temperature Sensor circuit has failed. The PCM switches the cooling fans to low speed operation once the engine coolant temperature falls below 105 °C (221 °F).

The PCM also activates high speed operation if the transaxle temperature exceeds 151 °C (304 °F). The PCM switches to low speed operation once the transaxle temperature falls below 115 °C (239 °F).

The PCM turns on the cooling fans at high speed if a low coolant level is detected and engine coolant temperature exceeds 85 °C (185 °F). The PCM switches to low speed operation once the engine coolant temperature drops below 80 °C (176 °F).

The Heater and A/C Programmer requests the PCM to turn on the cooling fans at high speed through the Class II data line if the A/C high side refrigerant temperature exceeds 64 °C (147 °F). The Heater and A/C Programmer requests that the cooling fans switch to low speed operation when the A/C high side refrigerant temperature falls below 51 °C (124 °F).

High Speed Operation
The cooling fans run at high speed when the PCM grounds Cooling Fan 1, 2, and 3 Relays on circuits, DK GRN (335) and DK BLU (473). With both Cooling Fan I Relay and Cooling Fan 2 Relay energized, battery voltage is applied to the LH Cooling Fan Motor through the relay contacts. The LH Cooling Fan Motor runs at high speed because the fan motor is grounded directly through WHT (504); the contacts of Cooling Fan 2 Relay, BLK (350) and ground G107.

Since Cooling Fan 3 Relay is also energized during high speed operation, battery voltage is applied directly to the RH Cooling Fan Motor through the closed contacts of the relay. The fan runs at high speed since it is no longer in series with the LH Cooling Fan Motor.

More info:
If the pressure in the cooling system is too low, or if the coolant does not contain enough ethylene glycol antifreeze, the coolant will boil without an overheat indication. Pure water can boil at 119 °C (247 °F) and the "TEMP" indicator will not show an overheat temperature, even with a 103 kPa (15 psi) cooling system. Refer to the Coolant Pressure/Temperature chart. Pure water lacks the necessary rust Inhibitors and coolant pump lubricant. The engine should never be run without the cap, or with the cap loose, as the coolant will boil before the temperature display shows a high temperature reading.

There is a way to command both fans low, and high speed through the IPC diagnostic override. I could find it in a factory service manual if I had one for 96 here at home, I have yet to locate the information in Alldata.