2003 Jaguar XJ8 Sport 114,000 miles on the clock. Over the winter I had a weird condition with the cooling fans staying on way too long. So I hooked up my scanner and I noticed that the coolant temp was holding at about 199 degrees. Which would cause the cooling fans to stay on, as they don't shut off until coolant reaches 194°. So I replaced the thermostat and that's solved that lingering 199° problems. But I've since noticed in the warm weather that the cooling fans come on as soon as I turn the car on even when the engine is cold anf the AC is off. Which I thought was pretty strange. Hook the scanner back up and I noticed that I'm having that same condition as before where the coolant temp only comes down to about 195 but not down to the 194 to shut the fans off. So I'm wondering what's making the fans stay on even when the coolant temp is cold. Is the ECM telling me that the cooling cycle is not correct by turning the fans on even when the engine is cold (temp sensor reading cold) and AC is off, just wondering I think this is pretty strange. So I'm going to swap out the coolant temp sensor with a new one and see what happens but I'm just intrigued that it's keeping the cooling fans on or commanding the cooling fans on even when the AC is off and the engine is cold. Thanks in advance.

 

So I did some looking around checked out the fan control module, everything seems fine there. So I unplugged the high pressure switch for the AC compressor and cooling fans on the AC side. And voila fans went off. Come to think of it I add it just a touch of freon maybe about 2 oz around the same time this problem occurred. So is it possible that I overfilled the system? But when I plug in the pressure switch for the AC the fans come on even with the AC shut off. Can anyone shed some light on the 5pin pressure switch for AC? Thanks.

 

The AC "pressure switch" contains two high pressure switches for the cooling fans control, one for low speed and one for high speed. Operation of the switches is shown in this table:

If any of the high pressure switches is faulty (stuck in closed position), it will cause the fans to run irrespective of whether the AC is on or off. Look for any signs of AC oil inside the connector of the pressure switch. Most likely, you need a new switch.

 

Thanks so much for info. So adding a lil freon, I about 3oz shouldn't make the pressure switch trip the fans with the AC off? I do have say tho, my cooling fans don't come on until the temp reaches 204, then shuts off at 194. What's up with that huh? Thanks in advance!

 

If you suspect too high pressure in the AC system, you should connect the AC pressure gages and see what you have. As for the fans switch-on temperature, I presume you are talking about the low fan speed. At what temperature do you get the high fan speed coming on? Where/how do you take the temperature measurement, is it accurate?

 

Yes I'm talking about the low fan speed. I'm pulling my temperature from a foxwell bidirectional scanner. And it's getting its temperature from the coolant temp sensor. I can't confirm on the high fan temp speed for coolant because my coolant temperature has never gotten that high. But it's like clockwork at 205 the low speed fans come on and it brings it down to 194 at which it shuts it off I've only owned the car for about 8 months but it has ran like that the whole time that I've owned it.

 

Just an update, replaced the pressure switch and that definitely cured the problem of the fans staying on all the time. It appears to switch was stuck. So I just want to thank you for that insight and let you know that the problem has been resolved again thank you.

 

The fans turning on at 204 is normal operation.