brewskih

After days of searching, and finally ordering a filed service manual, I was finally able to figure out the sequence of operations for the cooling fans. Since I was unable to find this information in any single post, I wanted to consolidate it here, to save others from days of searching, if the moderators will allow.

First, contrary to many posts I read BOTH fans operate together, at the same time. There are four factors that control when and what speed the operate on. They are three speed fans, with low medium and high speeds.

The four factors that determine their operation are, engine coolant temperature, your driving speed, the AC refrigerant pressure, and whether the AC is on or not.

The first condition is when the AC is turned OFF. The cooling fans will come on automatically on low speed when coolant temp reaches 203 degrees. They will go back off any time you are traveling more then 50 mph. They will switch to medium when coolant temp reaches 212 degrees. They will then switch to high when coolant temp reaches 221 degrees. Medium and high stay on regardless of speed travelling.
So which relay turns on both fans on low speed? Relay 2 which only uses one pole, turns fan on low speed. It does this by connecting both motors in series with each other. Positive battery power goes into terminal 1 of motor 1. That positive power goes through motor 1 winding and out terminal 4 of same motor, it then goes into relay number 2(which is energized), comes out relay 2 and goes to terminal 2 of motor 2. It goes through motor 2 winding and exits out terminal 3 to Ground. Now you have a complete circuit positive on motor 1 to negative on motor 2 and both motors turn on slow speed.

Now if the coolant temperature continues to rise to 212 degrees the fans will switch to medium speed. They do this using the following sequence. Relay 2 turns off(de-energizes) and relay 1 turns ON(energizes) Relay 1 uses both poles, one feeds positive voltage and the other feeds negative. Relay 1 feeds negative to terminal 3 of motor 1. Terminals 1 and 2 already have positive volts applies. So motor connected to terminal 2 and 3 has a complete circuit and runs. At the same time, relay 1 provides positive voltage to terminal 1 of motor 2. Terminals 3 and 4 of motor 2 are connected to ground, so the winding's connected to terminals 1 and 4 have a complete circuit and that motor runs as well.

Now its really hot outside so the coolant temp is still rising and reaches 221 degrees. Now the fans switch to high speed. Relay one stays ON(energized) and relay 3 turns on .. Relay 3 now provides negative power to terminal 4 of motor 1. Now we have relay 1 providing negative power to terminal 3, and relay 3 providing negative power to terminal 4. So the winding connected to 2 and 3 has negative and positive power and that winding is energized. Also the other motor winding connected to terminals 1 and 4 on motor 1 is energized and we have high speed.
Relay 3 now also supplies positive power to motor 2 terminal 2. So the motor 2 winding connected to terminals 2 and 3 now has positive and negative power and that winding is energized. The winding connected to terminals 1 and 4 is still energized from relay one so we now have high speed on this motor.

So you probably noticed by now. MOTOR 1 is directly connected to positive voltage, and the relays supply the negative. MOTOR 2 is set up exactly the opposite. Two terminals are directly connected to ground, and the relays provide the positive voltage.

OK....so that was the sequence of operations with the AC turned OFF. Now lets look at what happens when the AC is turned on.

When AC is on both fans will come on slow speed at any engine coolant temp and refrigerant pressure is below 185.6 psi. Once you are going over 50 miles an hour they will turn off unless your temp increases to one of the temps described above. At 221 degrees coolant temp they do not turn off of high speed regardless of how fast you are driving.

OK.....so now your refrigerant pressure rose above 185.6 but is below 229.1 psi. Your fans will operate on medium speed for the lower 2 coolant temperatures, and will switch to high when your coolant reaches 221 degrees. So under these conditions there is no slow speed operation. its either medium speed or high speed.

OK....now its so hot your AC is struggling and your AC refrigerant pressure rises above 229.1 psi. Your fans will only operate on high speed, regardless of engine coolant temperature, and regardless of how fast you are driving.

So to recap.....cooling fan motor 1 has two sets of winding's. One set is connected to terminals 2 and 3 of plug and other winding is connected to terminals 1 and 4. Terminals 1 and 2 are connected to positive voltage any time key is on, and the other side of winding's gets its negative from the relays. Cooling fan 2 is the opposite and terminals 3 and 4 are connected to negative ground, and terminals 1 and 2 get their positive volts from the relays.

Cooling fan 1 the red wire with yellow stripe is positive and connected to terminals 1 and 2. The red wire on terminal 3 comes from relay 1, and must provide negative for fan to operate on medium speed. The blue wire with black stripe, either feeds through relay 2(if energized) for slow speed or gets negative volts from relay 3 for high speed.

Cooling fan 2 the black wire is ground(negative volts) and is connected to terminals 3 and 4. The red wire with white stripe connected to terminal 1, gets positive voltage from relay 1 for medium speed. The blue wire on terminal 2 is either connected to motor 1 through relay 2(when energized) for slow speed, or gets its positive voltage from relay 3 for high speed.