aircon clutch not working

I'm dumb about most things with cars but even dumber about matters aircon. So basically when I press the aircon button I can't hear the clutch engaging. I know aircon can be problematical with coupes but is there a known culprit or best to get it to a specialists? I borrowed a mate's pressure reader and connected it to the appropriate valve and there's no pressure whatsoever. Also am I right in thinking that the fuse / relay for the aircon is under the bonnet somewhere

If there's no pressure then the compressor won't engage to avoid damage. Condenser is most common part to leak so I'd start by replacing that (and the dryer/filter) then get a leak test and re-gas if OK.

If the clutch engages you will see the inner wheel on the compressor move with the outer wheel (the pulley). Usual cause is loss of refrigerant causing low pressure, and the low pressure switch signal means that A/C ECU won't let the compressor run.

IIRC early cars had the fuses and relays in the black box above the washer reservoir, on later cars the box was done away with (presumablt due to owner spilling washer fluid all over the black box) and the fuse/relays were scattered around the engine compartment (near the maxi fuses I think?)

You'll need to get a "vac and re-gas" (vacuum out all refrigerant first, test for leaks, then refill with refrigerant and compressor lubricant, plus usually a fluorescent green dye to make leak detection a little easier).

Any of the O rings can leak, the condenser at the front can split/leak, or any of the pipes can leak if anything keeps rubbing on them (even a P clamp that's supposed to stop them moving around) and the compressor can leak if the casing gets small cracks/splits. It can be a long journey to try and find the root cause of non-functioning A/C, of which there may be several, including a faulty A/C ECU or other electrical issues.

The pipework itself can throw up leaks especially near the bends.

My a/c guy is a wizard and has replaced the bottom pipe with a heavy duty hose which is a lot more flexible and less likely to corrode!

At Thirlestane it should have been working nicely but 3 days before a pinhole leak presented itself right in front of our eyes on top of the rad, rhs!

Being wet on the Friday he couldn't re-manufacture the length of pipe as planned, but later this week...

+1 though for condensor and drier....

Thanks for your input peeps. At garage at the mo and about to a run a dye test. Hoping it's a pipe leak somewhere but I doubt it'll be as simple as that..

Well waddya know - hooked up the machine did all the vacuum stuff then against all expectations accepted the oil and the refrigerant and it's all sorted .. Mechanic couldn't believe it either so after £50 and back slapping drove off nice n chilled. Of course there could be small leak somewhere but the dye will show this up. Note to self - need to be a bit less pessimistic about the car

Good result