Chrysler Repair: air conditioner clutch goes/no goes, refrigerant charge, volt ohmmeter

Question
i have a 1999 lxi coupe. some times when i put the
ac on the button lights up but clutch on the compressor dose not ingage. when it dose ingage it works fine. do you have any idea what might be wrong?
                              thanks mike

Answer
Hi Mike,
It turns out that there are 11 possible reasons why the a/c clutch does not engage. The main one, I believe, is that the pressure of the refrigerant in the system is at the margin of acceptable. It is measured by a double pressure switch and I can imagine that from moment to moment if the amount of refrigerant is at the margin that it might allow the clutch to engage or not. Most of the other control factors involve electrical or mechanical controls that are more likely to be failed or o.k. but even these could be marginally operational. The only way to know for sure is to check thru the circuit electrically and find out where the request for the clutch to operate is breaking down. If you have a volt-ohmmeter and an interest in circuit checking I could xerox and mail the wiring diagrams. But if you haven't had the refrigerant charge checked lately that is where I would begin. You can check the system qualitatively by reference to the sight glass located in a round container near the comressor in the corner of the engine compartment: operate the a/c on max cool with fan blowing for a few minutes; then if you see small bubbles in the window it is a sign that the refrigerant level is low.
Roland