After watching my engine coolant temperature continuously rise when using the AC, I decided to utilize the auxiliary electric cooling fan to help out. You have all helped me out in the past so I wanted to return the favor. I documented the experience and include it here for you.








Why: The 1995 XJS has only an engine driven fan for cooling the engine, transmission cooler and AC Condenser. This causes the operating temperature of the coolant to rise and affects the efficiency of the AC system. The auxiliary electric fan is only used to prevent overheating conditions and is not used to assist otherwise. When the AC is on, the AC Condenser releases heat which then gets pulled through the engine coolant radiator since it is positioned in front of the radiator, causing a rise in coolant temperature. My project was to add a second circuit to drive the auxiliary cooling fan at half speed at any time the AC was operating creating a two-stage electric fan like that used on many production vehicles. This additional air flow helps keep the coolant temperature down and also improves the efficiency of the AC system. This installation has decreased my coolant temperatures when using the AC. I have documented my experience for your use if you like.


Parts List:

• One - SPST Relay – 12V, 30amp – Available from Advance Auto/Autozone etc. for about $6
• One - Relay socket – Not required but makes for a neater install. Acquired for around $10…..can be found for less
• Suitable lengths of #12 stranded automotive wire. Color doesn’t matter as long as you keep up with what attaches where.
• One – 1.5 ohm 100W Power Resistor. Available from Mouser Electronics.
  
  1. 284-HS100-1.5F, HS100 1R5 1%, 100W 1.5 1%
  2. $12.22 each plus shipping
• Shrink tubing to seal the soldered and crimped joints
• Silicone rubber to seal the splices
• Various crimp connectors and wire splicers of your choosing

Procedure: The objective of this procedure is to establish a separate circuit to the auxiliary electric fan that will drive the fan motor at one half speed whenever the AC is turned on. The circuit driven/controlled by the radiator coolant temperature sensor will still run the fan at full speed whenever the coolant temperature reaches the sensor’s trigger temp whether the AC is on or not.


So, basically what this does is use the +12V off of the AC Clutch relay when it is triggered to trigger another relay (the new one) that will provide a +12V path to the auxiliary fan motor through a power resistor. The power resistor is approximately the same impedance/resistance as the fan motor so the +12V will be divided between the motor and the resistor. The motor will receive about +6V resulting in it running at one half speed. I measured the non-running resistance of my auxiliary fan motor and got 1.3 ohms. The closest power resistor that I could find was 1.5 ohms. Close enough! You might want to measure your auxiliary fan motor’s resistance……………….it could be different. So the trick is to get a power resistor as close as possible to the resistance value of your fan motor. The modified Jaguar schematic showing the added circuit is included in the attachments.


Steps:

• Run a wire from the AC Clutch Relay RED/BROWN wire to Pin 85 of the New Relay.
• Run a wire from the New Relay, Pin 86, to Ground. I used the Ground stud located on the Driver side (US) of the radiator (Picture included). It is important to remove the air box to gain sufficient working room and to reveal the ground stud. You will see other wires attached to this stud.
• Run a wire from the New Relay, Pin 30, to the Brown/Green wire on the Cooling Fan Relay, Pin 87. This will provide the +12V needed for the new circuit.
• Run a wire from the New Relay, Pin 87 to the New Power Resistor. Mount the Power Resistor on the horizontal metal panel that the Auxiliary Fan mounts to using thermal paste and a couple of sheet metal screws. The thermal paste along with the metal panel will provide adequate heat dissipation for the Power Resistor. I placed the resistor in front of the auxiliary cooling fan to take advantage of the air flow. CAUTION: The Power Resistor gets VERY HOT when in use!! Don’t grab it. You will get burned.
• Run a wire from the other side of the New Power Resistor to the Black/Green wire of the Auxiliary Fan.
• Dress up your wires and make it neat. Also make sure any wiring cannot fall and rest on the New Power Resistor. As I have said previously, it gets HOT!! You don’t want to be melting any wires and causing fires.

 

I love this place! I know this post is 6 years old (day after tomorrow), but it was exactly what I needed on my Sunday morning. I recently replaced the radiator with an all-aluminum eBay purchase, and also took out the mechanical fan and put in two new electric fans. Its working great, but it sometimes works too well. I'm using a thermostatic switch in the radiator bung for those electric fans, so they don't kick in until 180F. Well, since that radiator works so well, if I am moving at all (even 10mph) the temp never gets to 180F and the fans don't kick in. This is fine most times, but now that we have had a couple of 90F days, I started to use my AC, and it isn't coming out very cold unless those fans are running, which they don't unless I'm sitting at a light for 3 minutes.

When I replaced everything, I removed the switch for the aux fan, so its just been sitting there dormant. I thought that if I could rig up that fan to run when the AC is on, that would cool down the condenser and lead to some cold AC. So I went looking on the forum and saw this. I modified a bit, since I don't need the regular switch for the aux fan, and I just spliced the 87 (red/brown) wire from the AC clutch relay to the 85 wire (green) on the Aux Fan relay. Then I grounded 86 to the common ground which is about 8 inches from the Aux Fan relay. Crisp and clean, no caffeine! Now when I turn on the AC, the aux fan kicks in and the AC blows cold. When I get up to temp, the two electric fans kick in and it blows REAL cold, even sitting at a light. Granted its only 80F outside this morning so I haven't tested it in the blistering summer, but I think I've got this one licked! Thanks cybercg!