Tapping/ticking that goes when AC turned on

[911_god]

Evening all

I've had what I thought was a sticky lifter...when the engine is hot, I get a tapity noise that goes as soon as I increased the revs. Everything runs well, was considering getting it sorted although the specialist says it's not really needed.

Come today and the warm weather, turn the ac on and the noise goes.it's like a tapity on/off switch. Any ideas what this could be??

 

[Thunderace]

Total guess but what you have said suggests the ticking is coming from the air con compressor.

If it ticks when air con is off and not when on perhaps it is the clutch mechanism of the compressor (I guess it must have one to freely spin when air con is off), why the ticking goes on increased revs even when air con is off would still be a mystery but sometimes ticking appears to go when it changes in pitch.

 

[Alex]

ECU increases the engine revs a couple hundred rpm when aircon is switched on. Lifters only tap at low revs. As soon as revs are increased the ticking goes. I'm guessing you're just on the threshold of this happening and when revs increase slightly, that's why the ticking goes.

 

[Thunderace]

Yeah mine was just a loose guess and I would probably defer to alexs' opinion anyway.

I think the "goes as soon as I increased the revs" is the part needing more info, was it just a few hundred rpm when the tapping goes?

 

[911_god]

Yeah mine was just a loose guess and I would probably defer to alexs' opinion anyway.

I think the "goes as soon as I increased the revs" is the part needing more info, was it just a few hundred rpm when the tapping goes?

The increase in RPM is almost unnoticeable, if I touch the accelerator or put the ac on it goes away instantly. What oil pressure should I be seeing when hot on idle?

 

[Alex]

Around 1 to 1.5 bar. Could also be the tiniest of weeps from an exhaust manifold whick also sounds like ticking.