Rhythmical clunk sounds from engine left side

Hi my 1st question here & just looking for ideas what this sound may me.

When idling there are rhythmical clunks from the left side of engine.

Louder clunk followed by a slightly faster/louder idling.
After around 13secs a quieter duller clunk followed by slower quieter idling.
After around 7secs it’s goes back to the louder clunk & the cycle repeats again.

The timing between each clunk carries a little. But seems to be a constant 20 seconds between each louder sound.

Not had the car a few months as a temporary run around & don’t know the history but generally it runs ok, it didn’t make these sounds when we got it.

Off on a longer trip & was a bit worried so Any ideas welcome. Thanks

Hi

You can't try running the engine with and then without the air con engaged, do the same for headlights/rear heater window on.

This may make a difference with the sound and point to air con compressor or alternator problem, just to try a few things.


Helpful would be a YouTube video that captures the sound, a minutes of the engine rythmical engine clunking sounds. You can add the YouTube here.

Just to add it’s from the left side as you look into the engine or right side as your sitting in the car.

Here’s a YouTube link with the louder clunk 1 second into it.

https://youtu.be/BLerR79p1kU

You can hear the engine rpm affected by the clonk sound. To me it sounds like the air conditioner pump clutch kicking in.

Try it with the air conditioner switch off and not blowing to remove this from the list of possibles.


You also have a few other sounds from the engine, but we can look at those later.

So with the:-

air com button off & fan not blowing = no clunks
Air con button on & fan at zero = no clunks
Air con on & fan on at level 1.2,3 or 4 = clunk sounds

To note it’s now around 1 minute between the louder clunk so not as consistantly they same timing as I thought.

I think that proves it's the air con clutch coming in and out. Mine makes that noise but not as frequently as yours.

You may be low on pressure in the air conditioner which means the pump has to be engaged more frequently (the air con clutch engages the a/c pump).

It's not a huge problem but the a/c system is working harder than it should and will wear out more quickly because of it.

At least you know how to stop it


There is also a tappety tap, not a big problem but it may benefit from an oil and filter change soon if it's not been done for a while.

That’s a relief that it’s nothing major for our trip.

Do you know , is it an easy diy job to repressurise air con system?

You need to take it to a professional that has the correct equipment to refill the a/c system. It is very important to get it done properly, the cost is around £60.

Many garages that's service cars can do this, but not all.

Arfur Dent

Thanks very much for all your speedy help!

I will check out having the Air Con service & that oil & filter change.

Enjoy your hot weekend.

LOL! When it gets to 40 you can call it hot! I'll let you know at Christmas when it's summer for me.

If you go to a reputable A/C mob they will check the pressures of the system first. That will tell you if there is enough gas in the system. If the pressures are OK they should not touch it (I.E. no regas). If the pressures are OK they may say there is not enough oil in the system and that's why the compressor is noisy. That will require a complete system flush and the correct quantity of oil added and a regas - not cheap! Of course they could do all that and it makes no difference, because there was nothing wrong in the first place! There is no "dip stick" for the compressor oil so it is impossible to tell if there is the correct amount of oil in the system! It's the Schrodinger's Cat of engineering! LOL!
On the surface it sounded normal to me but it's difficult to tell from the video. The big "clack" you can hear is the electro clutch on the compressor cutting in and it sounds fine to me. Some compressors can sound loud when running but be perfectly normal. "loud" can be subjective.

If it's hot and you select the A/C to max cold, the compressor will cut in and out more often anyway. If the compressor is not doing it's job, it tends to run longer not more often. More often tends to tell me that it is actually getting cold faster and then cutting out.

I have found the air-condition systems of the Citroen C2 and C3 (which are the same) just "acceptable" for Australian conditions and would never say they got "cold". If the cabin temperature keeps you comfortable and cool enough, I would consider the system serviceable and would leave it alone. However if you are unhappy with the performance, for one reason or another, then get it investigated.