Just had my air con regassed. Works fine, nice and cold, engine idles up when the compressor engages.

However, there's a rattle coming from somewhere when the AC is on and the clutch is engaged. When I disengage the clutch the rattle goes.

Air con off, no rattle clutch engaged or disengaged.

WTF?

 

Nobody?

 

Probably something just loose and shaking. Does it sound internal? Is there an air pump?

 

Yes I still have my air pump.

Possibly could be clutch spring rattle I guess, just odd that it's only present with AC On and clutch pedal up.

Depress clutch pedal and the noise goes.

Aircon was not functional before the regas, the system was empty.

 

I believe your AC pump has some issues. The AC pump should clutch-off when the car is at WOT or the clutch is depressed, iirc.

 

Ah now that's interesting....

Can anyone confirm that the AC compressor definitely declutches its magnetic clutch when the foot clutch is depressed?

If so then the ac compressor could be the main culprit and may explain why the previous owner hadn't bothered to re-gas the AC.

 

Just went out for a drive, started the car, no rattle AC on or off. Drove 10 miles with AC off, stopped for fuel.

No noise AC on or off at the petrol station.

Drove home 10 miles with AC on. Got out of the car and the rattle was evident immediately. Again turned off AC, noise goes. Turn on AC, noise returns.

If I put the AC on, depress the clutch and then slowly let the clutch up, I can hear the noise starting quietly as the pedal reaches the top of the travel, then getting louder as I totally release the pedal.

Lying on the floor next to the car it sounds like the noise is coming from too far back to be the AC Compressor.

Adjusted idle up and down with AC off, cannot induce the noise.

 

Unplug the air pump

 

Why? The noise isn't coming from the air pump.

 

When you say clutch, you're talking about the clutch clutch....the one that's between the engine and transmission, and not the compressor clutch, right?

If so, my car does the exact same thing.

As far as I can tell, it is the input shaft on the trans rattling around.

I dunno if the increased idle speed when the A/C is on causes a weird resonance, or if the pulses of the compressor drawing power to compress the refrigerant are causing some sort of driveline resonance, or who knows.

 

Yep, the foot operated transmission clutch

OK - good to know someone else has the same issue, and it makes sense as the noise seems like its coming from the back end of the engine/front side of the box.

How long has yours been like this?

Do you think the input shaft is worn perhaps?

I tried adjusting idle speed with AC off to check if the idle speed caused the noise but I found no effect, so more likely its a resonance or pulsing issue when the compressor is running.

Anyways, I feel better about taking the car on track next week now.

Thanks

 

Mine has been doing it ever since I bought it back in 2000.

I don't think anything is excessively worn, I think it is just one of those odd quirks of resonance in a rather complicated system.

 

OK good to know, thanks for putting my mind at rest

 

So I think my compressor is screwed. The AC stopped working a couple of days after my last post. I can still see the gas being pumped around by looking at window on top of the drier, but it doesn't blow cold.

Then out for a drive yesterday I noticed what sounded like a hissing noise which got louder with revs and was only present when the AC was switched on.

Long run plan is to replace compressor, condenser and drier.

 

What refrigerant do you have in the system? If you have R-12 and you're seeing a cloudy sightglass then you're more than likely low on refrigerant.

Replace the condenser? Is something wrong with it?

 

R134a.

My current condenser is old and corroded, plus some of the fins have come loose in the uppermost and lowermost rows