QuestionQUESTION: hello, thanks for taking my question.
i have a 1999 jeep Cherokee, 4.0l six.
i have gone through what i think is a long list of 1st order troubleshooting. basically the ac system works perfect until the engine reaches warmed up temp. once this happens, every thing "works" except the clutch/compressor does not engage. it will only work when the entire engine has cooled down(overnight). everything is good, professional refrig check, new electric fan, thermostat, etc. most components of the ac look new !!!
thanks for your help
ANSWER: Frank,
When you say new thermostat, do you mean a new electrical thermostat for the A/C or a new thermostat for the radiator? I ask this so that I can ask this next. Does your jeep temperature gauge register any higher than normal? I wouldn't have asked this a couple weeks ago, but... all of these different models of vehicle questions have taught me something. In some vehicles, if the engine begine to overheat, the PCM shuts down the A/C so that the radiator will be able to cool more effeciently without the condensor heat being added to it. In these cases, the questioners replaced their coolant thermostat, and everything began working perfectly. Always learning something new.
If this does not work, or if you have already replaced the engine thermostat, do a follow-up with me and I will talk you through the wiring checks. You will need a multimeter to do these checks.
Thank you for the question, and if I can do anything further do not hesitate to ask.
---------- FOLLOW-UP ----------
QUESTION: Well, i am proud to say i think like you. i had noticed that the temp was running hot ~210. i looked into it and i did replace the coolant thermostat.It now has a working 195f thermostat. the 195f is stock.so basically everything i described eailier was with the coolant thermostat replaced. i noticed today that the ac will cut out around 160f, as the engine is warming up
As far as the wiring goes, here are a few hot fingers that i tried. As i described above, everything is working except the compressor...if i pull the low pressure side sensor wire, the fan stops and the idle goes down. do i assume that this sensor is working? i perform the same procedure to the high pressure side and achieve the same results.
I also disconnected the wire that goes to the ac clutch while under the fault conation and found ~I've at the source side. i am not sure if the voltage gets to the inside of the clutch.
shoot.... i didn't realize the question would be answered so fast....i will rate the article, huge help already...
thank Dave
PS...if you have any questions regarding semiconductors, i have been an electronic engineer for over 22 years
AnswerFrank,
With your background, would it be easier for me to email you the schematic for your A/C. You could probably teach me a a bit. :))
But quick question. You said that you checked the compressor wire and got ~ . I've been doing residential A/C for as long as I have vehicles, and this symbol in my world means hertz. Did you mean that you had voltage on the DK Blue/Black wire feeding your clutch? If so, that narrows the problem down to your clutch itself real quick.
As for you disconnecting your pressure switches and the results, yes, for now we can assume that they are good.
