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View Full Version : 2000 XJ Sport A/C Intermittent Failure?


rbarton
July 7th, 2007, 05:19
My daughter just purchased her first vehicle, a 2000 XJ. The A/C will blow cold then just start blowing warm air after a time, especially if cutting back on the blower a bit. If we turn off the A/C (go to vent, etc.) after a few minutes, it will start blowing cold again once moved back to the A/C side. I checked the freon/pressure and it is perfect, dead on. I added a little, just to see if it made any difference. It didn't. One thing that is different on her 2000 as opposed to my 1996 is that when I turn on the A/C in mine, the electric fan starts immediately. Her 2000 can run for up to 10 minutes with the A/C on before the fan will kick in, but then it seems to cycle on an off normally. Is this a change between the years (computer, sensors, etc.) or should it come on immediately as well once the A/C is engaged? I think only someone with a 2000 or newer might be able to answer that one accurately. Past experience says expansion valve could be acting up, but so could the low pressure switch. I am trying to catch it when it does it so I can see what the clutch and fan are both doing at that time. Any ideas? The kid has saved her own money for an XJ since she was about 10 years old because she loved the two I have owned and she wants to work on it and pay for this stuff herself (what a rare concept for a teenager, but we'll have to sneak in and help her out a bit on the insurance) so any insight you can offer will be greatly appreciated. Thanks!

tommyr
July 7th, 2007, 06:20
Gotta look & see if the A/C clutch is cycling or not. In recirculate, especially in hot weather, the clutch should just about NEVER cycle (except while driving under heavy load). Did you check the pressure with a manifold gauge set? The first suspect is of course the pressure; clutch will cut out when low side gets to about 28lbs.
HTH

Tim_MN
July 7th, 2007, 06:22
On my 2000 the electric fan seems to be temp related only. If I turn on the A/C the fan does not turn on until the temp gauge goes over approximately 220. The fan will cycle on and off based on the temp and the airflow from driving.

Check the vacuum ball and vacuum hoses for leaks. It sounds as if maybe the blend door is slowly changing its setting as the vacuum drops. If you had a complete lack of vacuum, the vents default to the defroster position no matter where the vent selector is located.

I have a slow leak in the system and the compressor clutch will start to cycle on and off when I am low on freon. After adding some freon the compressor stays engaged.

alfman
July 7th, 2007, 07:53
Glad to hear some teens try to be self sufficiant. If the refridgerant is where it should be as far as pressure, another culprit could be the low pressure cut out switch could be defective.

rbarton
July 7th, 2007, 09:23
Thanks for the replies...keep 'em coming :)

I need to wait until it happens and stop right then and there to see if the compressor is running or not. If it is not, then I would think it's time to start looking at the various components one by one (pressure switch, expansion valve, etc) providing the clutch isn't just slipping. Checked the pressure again while all was running properly and it is where it should be. Temperature in the vehicle at the duct is around 58-62 degrees. I believe that is within spec.

Glad to hear the fan is apparently working as it should be too. That was a concern and is now eliminated. I have seen posts concerning 98-01 XJs doing very similar things with the A/C so I'm not feeling very confident about this right now. I do know that if the answer can be found, it is on NAXJA!

tommyr
July 7th, 2007, 10:16
Thanks for the replies...keep 'em coming :)
Checked the pressure again while all was running properly and it is where it should be. Temperature in the vehicle at the duct is around 58-62 degrees. I believe that is within spec.
If all is running properly, the pressure will be where it should be.
I dont have my FSM in front of me but the duct temperature is related to the ambient temperature. (You will only get a so many degree drop at the duct depending on the outside temperature) What you want is to check the low side pressure when it is not working correctly. If that pressure is below about 28lbs, the clutch will not engage.

UNCC_99XJ
July 7th, 2007, 13:56
Is it a change on the 2000 model year with the fan not running with the a/c? On my 99, and every other 4.0 XJ i've seen, as soon as the a/c kicks on, the fan comes right on with it.

Ivan
July 7th, 2007, 14:03
Sounds more like your low pressure switch has failed, which is really common in later model XJ's. What you are experiencing is that the evporator is icing up, because of the continual running of your AC system. Once the evaporator ices up, air flow is restricted due to the ice build up and all you get is luke warm air. Once the ice melts, the system works fine until it ices up again, and the cycle repeats.

Do you notice large amounts of water underneath your rig after it's been sitting a while...that's the ice melting off.

The low pressure switch is easy enough to replace. It's the switch that sits on top of the acumulator/drier. You simply unscrew it and replace with new. You don't have to discharge your system, as there is a shraeder valve that keeps the R134 in place while you change out the low pressure switch...