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The A/C clutch isn't usually associate with a ticking sound, usually more of a scraping/grinding sound. What must be happening is that the engine is under load when the A/C compressor is on and that changes the conditions behind the ticking.
Injectors on the B234F (and all LH systems) use a pulsed electric solenoid and always tick a little. In some engines that ticking can become very noticeable and may well indeed be what you're hearing. Whether it's a sticking injector (not overly common) or a fuel pressure related issue (maybe more common) or something else that makes them louder I'm not sure, but I've seen complaints here.
There is one quick test that may help you decide if the injectors are causing the noise. You do this at the OBD diagnostic connector at the left front strut brace as follows:
Function 3 will exercise some of the engine outputs. To enter function 3: turn the A/C off (and out of defrost position); turn ignition on (car not running); put OBD selector wire in socket #2 (fuel system); press button three times (hold button 1-3 seconds each time when pressing); LED should start flashing. While it is flashing the OBD system will continually cycle through some tests:
a) You will hear the injectors ticking as they are being opened and closed. Put your hand on each one to feel the clicking. If any one sounds significantly different from the others then there may be a problem.
b) You will then hear the IAC (idle air control valve under the intake manifold) being fully opened and closed. Put your hand on it to feel a solid thunk at the end of travel.
c) If present, you will then hear the solenoid valve (at left front fender) ticking as it is being opened and closed.
d) If present, you will then hear the cold start valve ticking as it is being opened and closed.
Possibly one of these noises will be similar to what you're hearing. Let the tests repeat a number of times to exercise the system. Disconnect the OBD test lead and restart the engine. If one of these devices was involved with your pesky ticking sound then you may have exercised it enough to notice a change.
The stethosocope approach is definitely worth a try. If you don't have a mechanics stethoscope then a 2-3 foot long wood dowel or metal rod will suffice as long as you're careful. Just hold the end of the rod firmly into the base of your thumb and stick your thumb nail into your ear so that your ear is sealed. Rather than pressing the end of the rod into where you're listening, it's safest to lay the side of the tip against the area of interest. Both the clarity of the sound and the loudness can help lead you to the source area.
BTW If you're doing you own B234F timing belt change this weekend, you may find the detailed article in the 700/900 FAQ covering that topic helpful. There are a few noteworthy things, like how to get the tensioner in and out, always putting in a new oil pump pulley bolt and the proper torque and tension specs.
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Dave -not to be confused with a real expert
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