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I have an odd A/C issue that is driving me up the wall now that we have been hitting over 100 with Pacific humidity. My A/C will run like a champ until the outside temp reads 72 or 74. Then the A/C cuts out and the fans hit high. I first noticed this on a recent Range Rover trip with the acclaimed Ron Beckett. Cruising downtown San Fran the A/C suddenly cut out. A week later on my return trip with temps hitting 95 I had no A/C. I had no issues until the past 6 weeks or so of high temps. I have been doing a bit of trouble shooting and note taking during this time. Reguardless of outside temp I have ice cold A/C for about 10-15 mintues. Then the A/C cuts out. I have forced recalibration of the blend/position motors and tested all stops for them... 100% working. My fuse box has been replaced at some point and shows as a shiney new penny. All relays check out and have been swapped around to make sure. Ron noticed that my clutch was about to fall out of my compressor thank to a loose nut. It hasn't budged since.

Sorry guys, I can rebuild an engine blind folded, but when it comes to A/C and all these **** switches I am a moron.

Hints and checks greatly appreciated.
 

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I don't know if I can help, but I think more information will be helpful to anyone who can. When you say the AC "cuts out," what happens exactly? Does the compressor stop running (i.e. the clutch disengages)? If the clutch is disengaging, does it ever cycle back on by itself?

Or, is it that the blend flaps adjust to giving no air flow through the evaporator even though the compressor is running? Are you set to auto or manual control? If auto, does the interior temp when "cut-out" occurs correspond with the set auto temp? I don't know where that question leads to.

I believe most AC systems have a refrigerant pressure sensor with high and low pressure cut-offs. If pressure is too high or too low, the clutch is de-energized. A possibility that you have too much or not enough refrigerant, or a pressure sensor that is haywire (if the problem is the clutch disengaging).

Do you think it might be the classic evaporator freeze up? Ice forms on the evaporator blocking air flow through it so you lose cooling. Air is still somewhat cool, but not near as cold as it should be. There is a temp probe inserted into the evaporator compartment which is supposed to tell the AC control unit that ice is forming. The control unit then cycles the compressor off and on to allow the evaporator to warm up to melt the ice. It's a continuous feed back thing. Perhaps your temp sensor or feedback circuit is botched.

Brett
 

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Had similar experience 2 weeks ago during a 6 hours trip to Bordeaux ( South West of France). The A/C worked normal on the way back to Paris and no worry since.
I had it refilled 2 months ago by a friend.
 

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2002-2005 Range Rover MkIII / L322
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Is the clutch engaging when the AC stops?

Has your car had the AC link harness mod done (I can't remember).
 

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Hi

I have had similar problems. The problem is most likely caused by the high pressure switch. The higher the temperature the higher the pressure. When the outside air gets hotter the condensation temperature rises and when it gets too high the high pressure switch cuts out the clutch which is detected by the HEAVAC ECU and the book sign lights up and the ECU will not supply any signal towards the clutch anymore. Stopping the engine and restarting in a minute or so will get the AC working again until high pressure switch cuts out again.

The high pressure can be caused by overfilling of the system with refridgerant. The liquid is accumulating in the condensor and the part of the condensor filled with liquid does not participate in the condensing process anymore. It can also be that the air flow is blocked or reduced. And last but not least the dryer/filter unit can be clogging up raising the differential pressure in combination with high temperature in the condensor it can trigger the high pressure switch.

The best way to determine the liquid level is to make a thermal scan. A second solution is by measuring the condensor temperature with an thermogun at locations from bottom to top and left to right. The lower part that is colder is filled with liquid. There should be a real defined line between hot and cold.

Releasing some of the gas can help to solve your problem. Do not release too much as this will cause lack of gas and the low pressure switch will cut out the AC.

Regards

Jos

Regards

Jos
 

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Are you talking blower motors or condenser fans?

As you mentioned recalibrating blend motors, etc. I was thinking interior and blower motors - which is similar to what mine has been doing since I bought it: I'm driving along all nice and cool minding my own bidness and suddenly I go from a mild spring day in New York to Florida in July (although the blower motor speed remains constant). I can get the A/C to catch itself by dropping the temp to LO on both sides. I've always assumed that its either a temp sensor (evap, ambient, or interior) or the HEVAC ECU. Its not happened often enough to get me to break out the multimeter.

If you were talking blower motors, it sounds as if your HEVAC ECU decided you need defrosting and went partially into the PROG defrost mode - bad, bad ECU. If you were talking condenser fans, Jos' diagnosis of an overfill does not sound unlikely - especially as the compressor low/high and fan high are separate switches.
 
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